tag:theconversation.com,2011:/us/topics/paleobiology-19086/articlesPaleobiology – The Conversation2024-03-27T12:37:29Ztag:theconversation.com,2011:article/2232682024-03-27T12:37:29Z2024-03-27T12:37:29ZHorses lived in the Americas for millions of years – new research helps paleontologists understand the fossils we’ve found and those that are missing from the record<figure><img src="https://images.theconversation.com/files/574775/original/file-20240211-26-t88v8r.jpg?ixlib=rb-1.1.0&rect=63%2C121%2C4179%2C2650&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">People have collected fossil horses throughout North America for centuries.</span> <span class="attribution"><span class="source">Florida Museum/Mary Warrick</span></span></figcaption></figure><p>Many people assume that horses first came to the Americas when Spanish explorers brought them here about 500 years ago. In fact, recent research has <a href="https://theconversation.com/archaeology-and-genomics-together-with-indigenous-knowledge-revise-the-human-horse-story-in-the-american-west-202222">confirmed a European origin</a> for horses associated with humans in the American Southwest and Great Plains.</p>
<p>But those weren’t the first horses in North America. The family Equidae, which includes domesticated varieties of horses and donkeys along with zebras and their kin, is actually native to the Americas. The <a href="https://doi.org/10.1126/science.1105458">fossil record reveals</a> horse origins here more than 50 million years ago, as well as their extinction throughout the Americas during the last Ice Age about 10,000 years ago.</p>
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<a href="https://images.theconversation.com/files/584586/original/file-20240326-30-4szthv.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="family tree showing horse evolution diversifying over time" src="https://images.theconversation.com/files/584586/original/file-20240326-30-4szthv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/584586/original/file-20240326-30-4szthv.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=741&fit=crop&dpr=1 600w, https://images.theconversation.com/files/584586/original/file-20240326-30-4szthv.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=741&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/584586/original/file-20240326-30-4szthv.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=741&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/584586/original/file-20240326-30-4szthv.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=932&fit=crop&dpr=1 754w, https://images.theconversation.com/files/584586/original/file-20240326-30-4szthv.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=932&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/584586/original/file-20240326-30-4szthv.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=932&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Phylogeny, geographic distribution, diet and body sizes of the family Equidae over the past 55 million years.</span>
<span class="attribution"><a class="source" href="https://doi.org/10.1126/science.1105458">From 'Fossil horses–evidence for evolution.' Science. MacFadden, 2005. Reprinted with permission from AAAS.</a></span>
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<p>We are <a href="https://scholar.google.com/citations?user=xhm6ez4AAAAJ&hl=en&oi=ao">paleontologists</a> <a href="https://scholar.google.com/citations?user=oZ8oBigAAAAJ&hl=en&oi=ao">who focus our research</a> on various types of fossils, including ancient horses. <a href="https://doi.org/10.1017/pab.2023.35">Our most recent work</a> used computer statistics to analyze gaps in the fossil record to infer more about which horse species really did and didn’t live in one ancient habitat in Florida.</p>
<h2>Horses evolved as ecosystems changed</h2>
<p>People have collected fossil horses throughout North America for centuries. Because horse fossils are abundant and widespread across the continent, scientists often point to the <a href="https://www.cambridge.org/us/universitypress/subjects/earth-and-environmental-science/palaeontology-and-life-history/fossil-horses-systematics-paleobiology-and-evolution-family-equidae?format=PB">long span of the horse family</a> as evidence of long-term evolutionary change.</p>
<p>Paleontologists like us, who study extinct mammals, almost never find complete skeletons. Instead, we focus on durable fossil teeth, which help us understand ancient diets, and fossil limbs, which help clarify how these animals moved.</p>
<p>Horses are eating machines. In the wild today, they primarily feed on grasses that don’t provide much nutrition, and thus they need to consume large quantities to survive. The large teeth of modern horses and their ancestors are adapted primarily for grazing on gritty grasses. They replaced smaller teeth of more primitive horses adapted to <a href="https://doi.org/10.1016/S0031-0182(01)00359-5">browsing on soft leafy vegetation</a>.</p>
<p>We know what horses ate millions of years ago by studying distinctive microscopic scratches, pits and other wear patterns on their teeth that were created <a href="https://doi.org/10.1016/j.palaeo.2015.11.004">as the ancient horses chewed plant foods</a>. And analyses of carbon preserved in fossil teeth show that <a href="https://doi.org/10.1016/0031-0182(94)90099-X">coexisting horse species ate different plants</a>; some browsed on leaves from bushes and trees, some grazed on grasses, and yet others were mixed feeders.</p>
<p>The change in tooth shape tracks the change in dominant vegetation types in North America, from tropical forests that then gave way to the <a href="https://doi.org/10.1146/annurev-earth-040809-152402">great expansion of open prairie grasslands</a>. As the climate and flora changed over millions of years, horses shifted from being largely forest-dwelling browsers to largely open-country grazers. Their teeth and feeding patterns adapted to the environment.</p>
<p>Another adaptation is visible on horses’ feet. Modern horses have one hoofed toe on each foot. Many extinct fossil horses – the ancient ancestors of today’s horses – had three toes per foot. The single toe on each elongated foot is good for rapid and sustained running to evade predators and for long-distance seasonal migrations. The more ancient three-toed feet provided <a href="https://doi.org/10.1038/308179a0">stability on unstable or wet ground</a>. The adaptation from three toes to one was likely in response to changing habitats.</p>
<p>But even as the environment changed, one distinct species didn’t completely replace another overnight. The fossil record in North America documents periods millions of years ago when multiple horse species coexisted on the ancient landscapes. Species were of different sizes and had teeth equipped for munching different plants, so they weren’t competing directly for the same foods. Different habitats within these ancient ecosystems likely had some species more adapted to forests and others more adapted to grasslands.</p>
<h2>Understanding Florida’s fossil record</h2>
<p>Paleontologists have been collecting horse fossils in Florida for over 125 years. The Florida Museum of Natural History at the University of Florida, where we work, has more than 70,000 fossil horse specimens from more than a thousand locations across the state.</p>
<p>One of our more <a href="https://www.floridamuseum.ufl.edu/florida-vertebrate-fossils/sites/montbrook/">prolific fossil sites, Montbrook</a>, provides a glimpse of a 5.8 million-year-old ancient stream bed. It preserved more than 30 extinct mammals, including rhinos, elephants and carnivores, as well as hundreds of bones and teeth of fossil horses.</p>
<p>Although six horse species are known elsewhere in Florida, we have only found four so far at Montbrook. This smaller number of horse species perplexed us, <a href="https://doi.org/10.1017/pab.2023.35">so we decided to investigate</a>. Did the two “missing” horse species truly not live at Montbrook, or have scientists simply not discovered their fossil remains yet?</p>
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<a href="https://images.theconversation.com/files/584451/original/file-20240326-26-8hew8y.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Representative fossil horse teeth of Florida" src="https://images.theconversation.com/files/584451/original/file-20240326-26-8hew8y.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/584451/original/file-20240326-26-8hew8y.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=784&fit=crop&dpr=1 600w, https://images.theconversation.com/files/584451/original/file-20240326-26-8hew8y.PNG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=784&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/584451/original/file-20240326-26-8hew8y.PNG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=784&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/584451/original/file-20240326-26-8hew8y.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=985&fit=crop&dpr=1 754w, https://images.theconversation.com/files/584451/original/file-20240326-26-8hew8y.PNG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=985&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/584451/original/file-20240326-26-8hew8y.PNG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=985&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Each of the six fossil horse species (A-F) found in Florida have distinct teeth. Scale bar = 1 centimeter.</span>
<span class="attribution"><a class="source" href="https://doi.org/10.1017/pab.2023.35">Killingsworth & MacFadden, Paleobiology, 2024</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">CC BY-NC-SA</a></span>
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<p>We designed a theoretical model that compares Montbrook, with only four horse species, to other fossil sites in Florida that contain all six. Using a statistical technique that scientists call “<a href="https://www.lancaster.ac.uk/stor-i-student-sites/jack-trainer/bootstrapping-in-statistics/">bootstrapping</a>,” our computer essentially simulated continued fossil collecting over time. We generated 1,000 theoretical fossil collection events based on the fossil species counts from the sites where all six are present, to predict the probability of collecting the species that are currently missing at Montbrook.</p>
<p>Results from our simulation show that the two missing horse species at Montbrook were absent for different reasons. One of the horses is likely to be truly absent; the other may still be discovered with further excavation.</p>
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<a href="https://images.theconversation.com/files/576220/original/file-20240216-26-vkk8pe.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="About a dozen people focused on digging in soil a few feet below the surface of surrounding landscape." src="https://images.theconversation.com/files/576220/original/file-20240216-26-vkk8pe.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/576220/original/file-20240216-26-vkk8pe.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=442&fit=crop&dpr=1 600w, https://images.theconversation.com/files/576220/original/file-20240216-26-vkk8pe.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=442&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/576220/original/file-20240216-26-vkk8pe.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=442&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/576220/original/file-20240216-26-vkk8pe.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=555&fit=crop&dpr=1 754w, https://images.theconversation.com/files/576220/original/file-20240216-26-vkk8pe.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=555&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/576220/original/file-20240216-26-vkk8pe.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=555&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Excavations are ongoing at the Montbrook fossil site in Florida.</span>
<span class="attribution"><span class="source">Florida Museum/Jeff Gage</span></span>
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<h2>Probing ‘gaps’ in the fossil record</h2>
<p>Knowing a species is absent is just as important as knowing when one is present at a fossil site. Absences may be indicators of underlying ecological and biological drivers changing population dynamics. Coupled with other types of analyses, researchers can apply this kind of predictive modeling across many fossil species and ancient landscapes.</p>
<p>Ever since <a href="https://www.britannica.com/biography/Charles-Darwin/Evolution-by-natural-selection-the-London-years-1836-42">Charles Darwin proposed his theory of evolution</a>, scientists have known that the fossil record is incomplete, resulting in gaps in our knowledge of the ancient past and evolutionary change. Paleontologists are challenged to explain these gaps, including which species were or were not present at particular fossil sites.</p>
<p>Gaps can result from certain materials, such as teeth and shells, which are often more durable than porous bone, fossilizing better than others. Likewise, different chemical conditions during fossilization, and even the amount of time spent collecting fossils at a particular site, <a href="https://doi.org/10.1016/j.earscirev.2023.104537">can contribute to the lack of knowledge</a>.</p>
<p>Fortunately, fossil horse teeth preserve quite well and are commonly found. As new discoveries are made, such as those from our ongoing excavations in Florida, they’ll help clarify and narrow gaps in the fossil record.</p><img src="https://counter.theconversation.com/content/223268/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Bruce J. MacFadden receives funding from the US National Science Foundation. </span></em></p><p class="fine-print"><em><span>Stephanie Killingsworth does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Horse fossils are abundant and widespread across North America. Scientists often use their long history to illustrate how species evolve in response to a changing environment.Stephanie Killingsworth, Ph.D. Student in Geological Sciences, University of FloridaBruce J. MacFadden, Distinguished Professor and Director of Thompson Earth Systems Institute (TESI), University of FloridaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2128132023-09-04T16:08:42Z2023-09-04T16:08:42ZHow did plants first evolve into all different shapes and sizes? We mapped a billion years of plant history to find out<figure><img src="https://images.theconversation.com/files/546238/original/file-20230904-29-nbmdbo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">From minuscule moss to colourful flowers and tall trees.</span> <span class="attribution"><span class="source">Philip Donoghue / James Clark</span></span></figcaption></figure><p>Plants range from simple seaweeds and single-celled pond scum, through to mosses, ferns and huge trees. Palaeontologists like us have long debated exactly how this diverse range of shapes and sizes emerged, and whether plants emerged from algae into multicellular and three-dimensional forms in a gradual flowering or one big bang.</p>
<p>To answer this question, scientists turned to the fossil record. From those best-preserved examples, like trilobites, ammonites and sea urchins, they have invariably concluded that a group’s range of biological designs is achieved during the earliest periods in its evolutionary history. In turn, this has led to hypotheses that evolutionary lineages have a <a href="https://www.pnas.org/doi/10.1073/pnas.1302642110">higher capacity for innovation early on</a> and, after this first phase of exuberance, they stick with what they know. This even applies to us: all the different placental mammals evolved from a common ancestor surprisingly quickly. Is the same true of the plant kingdom?</p>
<p>In our <a href="https://www.nature.com/articles/s41477-023-01513-x">new study</a>, we sought to answer this question by looking for certain traits in each major plant group. These traits ranged from the fundamental characteristics of plants – the presence of roots, leaves or flowers – to fine details that describe the variation and ornamentation of each pollen grain. In total, we collected data on 548 traits from more than 400 living and fossil plants, amounting to more than 130,000 individual observations.</p>
<p>We then analysed all this data, grouping plants based on their overall similarities and differences, all plotted within what can be thought of as a “design space”. Since we know the evolutionary relationships between the species, we can also predict the traits of their extinct shared ancestors and include these hypothetical ancestors within the design space, too. </p>
<p>For example, we will never find fossils of the ancestral flowering plant, but we know from its closest living descendants that it was bisexual, radially symmetric, with more than five <a href="https://pubmed.ncbi.nlm.nih.gov/28763051/">spirally arranged carpels</a> (the ovule-bearing female reproductive part of a flower). Together, data points from living species, fossils and predicted ancestors reveal how plant life has navigated design space through evolutionary history and over geological time.</p>
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<a href="https://images.theconversation.com/files/546215/original/file-20230904-19-zqsi5h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Annotated chart of plants" src="https://images.theconversation.com/files/546215/original/file-20230904-19-zqsi5h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/546215/original/file-20230904-19-zqsi5h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=552&fit=crop&dpr=1 600w, https://images.theconversation.com/files/546215/original/file-20230904-19-zqsi5h.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=552&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/546215/original/file-20230904-19-zqsi5h.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=552&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/546215/original/file-20230904-19-zqsi5h.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=694&fit=crop&dpr=1 754w, https://images.theconversation.com/files/546215/original/file-20230904-19-zqsi5h.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=694&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/546215/original/file-20230904-19-zqsi5h.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=694&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">The two axes summarise the variation in anatomical design among plants. Coloured dots represent living groups while the black dots represent extinct groups known only from fossils. The lines connecting these groupings represent the evolutionary relationships among living and fossil groups, plus their ancestors, inferred from evolutionary modelling. (The chlorophytes and charophytes are marine and freshwater plants while the remaining groups are land plants. Angiosperms are flowering plants).</span>
<span class="attribution"><span class="source">Philip Donoghue et al / Nature Plants</span></span>
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<p>We expected flowering plants to dominate the design space since they make up more than 80% of plant species, but they don’t. In fact, the living bryophytes – mosses, liverworts and hornworts – achieve almost as much variety in their body forms. </p>
<p>This may not be entirely surprising since the three lineages of bryophytes have been doing their own thing for more than three times as long as flowering plants. And despite their diminutive nature, even the humble mosses are <a href="https://theconversation.com/the-secret-world-of-moss-ancient-ancestor-of-all-plants-and-vital-for-the-health-of-the-planet-205048">extraordinarily complex and diverse</a> when viewed through a microscope.</p>
<p>The evolutionary relationships conveyed by the branching genealogy in the above plot show that there is, generally, a structure to the occupation of design space – as new groups have emerged, they have expanded into new regions. However, there is some evidence for convergence, too, with some groups like the living gymnosperms (conifers and allies) and flowering plants plotting closer together than they do to their common ancestor. </p>
<p>Nevertheless, some of the distinctiveness of the different groupings in design space is clearly the result of extinction. This is clear if we consider the distribution of the fossil species (black dots in the above figure) that often occur between the clusters of living species (coloured dots in the figure).</p>
<h2>So how did plant body plan diversity evolve?</h2>
<p>Overall, the broad pattern is one of progressive exploration of new designs as a result of innovations that are usually associated with reproduction, like the embryo, spore, seed and flower. These represent the evolutionary solutions to the environmental challenges faced by plants in their progressive occupation of increasingly dry and challenging niches on the land surface. For example, the innovation of seeds allowed the plants that bear them to reproduce even in the absence of water.</p>
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<a href="https://images.theconversation.com/files/546219/original/file-20230904-17-y48vej.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Close up image of moss" src="https://images.theconversation.com/files/546219/original/file-20230904-17-y48vej.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/546219/original/file-20230904-17-y48vej.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/546219/original/file-20230904-17-y48vej.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/546219/original/file-20230904-17-y48vej.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/546219/original/file-20230904-17-y48vej.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/546219/original/file-20230904-17-y48vej.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/546219/original/file-20230904-17-y48vej.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Moss might seem simple – until you zoom in.</span>
<span class="attribution"><span class="source">ANGHI / shutterstock</span></span>
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<p>Over geological time, these expansions occur as episodic pulses, associated with the emergence of these reproductive innovations. The drivers of plant anatomical evolution appear to be a combination of genomic potential and environmental opportunity.</p>
<h2>Plant disparity suggests that the big bang is a bust</h2>
<p>None of this fits with the expectation that evolutionary lineages start out innovative before becoming exhausted. Instead, it seems fundamental forms of plants have emerged hierarchically through evolutionary history, elaborating on the anatomical chassis inherited from their ancestors. They have not lost their capacity for innovation over the billion or more years of their evolutionary longevity. </p>
<p>So does that make plants different from animals, studies of which are the basis for the expectation of early evolutionary innovation and exhaustion? Not at all. Comparable studies that we have done on <a href="https://theconversation.com/how-animals-went-from-single-cells-to-over-30-different-body-types-102602">animals and fungi</a> show that, when you study these multicellular kingdoms in their entirety, they all exhibit a pattern of episodically increasing anatomically variety. Individual lineages may soon exhaust themselves but, overall, the kingdoms keep on innovating. </p>
<p>This suggests a general pattern for evolutionary innovation in multicellular kingdoms and also that animals, fungi and plants still have plenty of evolutionary juice in their tanks. Let’s hope we’re still around to see what innovation arises next.</p><img src="https://counter.theconversation.com/content/212813/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Philip C J Donoghue receives funding from the Natural Environment Research Council, Biotechnology and Biological Sciences Research Council, The Leverhulme Trust, Gordon and Betty Moore Foundation and the John Templeton Foundation. </span></em></p><p class="fine-print"><em><span>James Clark receives funding from the Leverhulme Foundation.</span></em></p><p class="fine-print"><em><span>Sandy Hetherington receives funding from UKRI.</span></em></p>Plants have not lost their capacity for innovation over the years, finds new study.Philip C J Donoghue, Professor of Palaeobiology, University of BristolJames Clark, Research Associate, School of Biological Sciences, University of BristolSandy Hetherington, Plant Evolutionary Biologist, The University of EdinburghLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2048882023-05-04T19:06:29Z2023-05-04T19:06:29ZReconstructing ancient bacterial genomes can revive previously unknown molecules – offering a potential source for new antibiotics<figure><img src="https://images.theconversation.com/files/523906/original/file-20230502-2182-swsnio.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C8256%2C5499&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Ancient DNA preserved in the tooth tartar of human fossils encodes microbial metabolites that could be the next antibiotic.</span> <span class="attribution"><a class="source" href="https://www.eurekalert.org/multimedia/983784?">Werner/Siemens Foundation</a></span></figcaption></figure><p>Microorganisms – in particular bacteria – are skillful chemists that can produce an impressive diversity of chemical compounds known as <a href="https://theconversation.com/nature-is-the-worlds-original-pharmacy-returning-to-medicines-roots-could-help-fill-drug-discovery-gaps-176963">natural products</a>. These metabolites provide the microbes major evolutionary advantages, such as allowing them to interact with one another or their environment and helping defend against different threats. Because of the diverse functions bacterial natural products have, many have been <a href="https://doi.org/10.1021/acs.jnatprod.5b01055">used as medical treatments</a> such as antibiotics and anti-cancer drugs.</p>
<p>The microbial species alive today represent only a tiny fraction of the vast diversity of microbes that have inhabited Earth over the past <a href="https://theconversation.com/were-viruses-around-on-earth-before-living-cells-emerged-a-microbiologist-explains-197880">3 billion years</a>. Exploring this microbial past presents exciting opportunities to recover some of their lost chemistry. </p>
<p>Directly studying these metabolites in archaeological samples is virtually impossible because of their <a href="https://doi.org/10.1007/s11306-017-1270-3">poor preservation</a> over time. However, reconstructing them using the genetic blueprints of long-dead microbes could provide a path forward. </p>
<p>We are a team of <a href="https://scholar.google.com/citations?user=cDFcc3cAAAAJ&hl=en">anthropologists</a>, <a href="https://scholar.google.de/citations?user=trnMQ7MAAAAJ&hl=en">archaeogeneticists</a> and <a href="https://scholar.google.com/citations?user=26MgwRgAAAAJ&hl=en">biochemists</a> who study ancient microbes. By <a href="https://www.science.org/doi/10.1126/science.adf5300">generating previously unknown chemical compounds</a> from the reconstructed genomes of ancient bacteria, our newly published research provides a proof of concept for the potential use of fossil microbes as a source of new drugs.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/524480/original/file-20230504-17-ivzxrf.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Researcher weighing tooth fossil on a scale" src="https://images.theconversation.com/files/524480/original/file-20230504-17-ivzxrf.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/524480/original/file-20230504-17-ivzxrf.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=565&fit=crop&dpr=1 600w, https://images.theconversation.com/files/524480/original/file-20230504-17-ivzxrf.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=565&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/524480/original/file-20230504-17-ivzxrf.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=565&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/524480/original/file-20230504-17-ivzxrf.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=710&fit=crop&dpr=1 754w, https://images.theconversation.com/files/524480/original/file-20230504-17-ivzxrf.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=710&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/524480/original/file-20230504-17-ivzxrf.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=710&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A single ancient tooth preserves the genomes of millions of ancient bacteria.</span>
<span class="attribution"><span class="source">Felix Wey/Werner Siemens Foundation</span></span>
</figcaption>
</figure>
<h2>Reconstructing ancient genomes</h2>
<p>The cellular machinery producing bacterial natural products is encoded in genes that are typically in close proximity to one another, forming what are called <a href="https://doi.org/10.1016/j.tim.2016.07.006">biosynthetic gene clusters</a>. Such genes are difficult to detect and reconstruct from ancient DNA because very old genetic material breaks down over time, fragmenting into thousands or even millions of pieces. The end result is numerous tiny DNA fragments <a href="https://doi.org/10.1038/s43586-020-00011-0">less than 50 nucleotides long</a> all mixed together like a jumbled jigsaw puzzle.</p>
<p>We sequenced billions of such ancient DNA fragments, then improved a bioinformatic process called <a href="https://doi.org/10.1007/s40484-019-0166-9">de novo assembly</a> to digitally order the ancient DNA fragments in stretches of up to 100,000 nucleotides long – a 2,000-fold improvement. This process allowed us to identify not only what genes were present, but also their order in the genome and the ways they differ from bacterial genes known today – key information to uncovering their evolutionary history and function. </p>
<p>This method allowed us to take an unprecedented look at the genomes of microbes living up to 100,000 years ago, including species not known to exist today. Our findings push back the <a href="https://doi.org/10.1038/s41586-021-03532-0">previously oldest</a> <a href="https://doi.org/10.1186/s40168-021-01132-8">reconstructed microbial genomes</a> by more than 90,000 years.</p>
<p>In the microbial genomes we reconstructed from DNA extracted from ancient tooth tartar, we found a gene cluster that was shared by a high proportion of Neanderthals and anatomically modern humans living during the <a href="https://www.britannica.com/event/Stone-Age/Middle-Paleolithic">Middle and Upper Paleolithic</a> that lasted from 300,000 to 12,000 years ago. This cluster bore the <a href="https://doi.org/10.1038/s43586-020-00011-0">molecular hallmarks of very ancient DNA</a> and belonged to the bacterial genus <em>Chlorobium</em>, a group of green sulfur bacteria capable of photosynthesis.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/524154/original/file-20230503-26-5xqprb.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Chemical structure of paleofurans produced using ancient microbial DNA." src="https://images.theconversation.com/files/524154/original/file-20230503-26-5xqprb.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/524154/original/file-20230503-26-5xqprb.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=280&fit=crop&dpr=1 600w, https://images.theconversation.com/files/524154/original/file-20230503-26-5xqprb.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=280&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/524154/original/file-20230503-26-5xqprb.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=280&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/524154/original/file-20230503-26-5xqprb.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=351&fit=crop&dpr=1 754w, https://images.theconversation.com/files/524154/original/file-20230503-26-5xqprb.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=351&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/524154/original/file-20230503-26-5xqprb.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=351&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">These paleofurans were produced from ancient microbial DNA.</span>
<span class="attribution"><span class="source">Pierre Stallforth</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>We inserted a synthetic version of this gene cluster into a “modern” bacterium called <em>Pseudomona protegens</em> so it could produce the chemical compounds encoded in the ancient genes. Using this method, we were able to isolate two previously unknown compounds we named <a href="https://www.science.org/doi/10.1126/science.adf5300">paleofuran A and B</a> and determine their chemical structure. Resynthesizing these molecules in the lab from scratch confirmed their structure and allowed us to produce larger quantities for further analysis.</p>
<p>By reconstructing these ancient compounds, our findings highlight how archaeological samples could serve as new sources of natural products. </p>
<h2>Mining ancient natural products</h2>
<p>Microbes are constantly evolving and adapting to their surrounding environment. Because the environments they inhabit today differ from those of their ancestors, microbes today likely produce different natural products than ancient microbes from tens of thousands of years ago.</p>
<p>As recently as <a href="https://www.doi.org/10.1007/978-1-4613-1145-4_1">25,000 to 10,000 years ago</a>, the Earth underwent a major climate shift as it transitioned from the colder and more volatile <a href="https://www.britannica.com/science/Pleistocene-Epoch">Pleistocene Epoch</a> to the warmer and more temperate <a href="https://www.britannica.com/science/Holocene-Epoch">Holocene Epoch</a>. Human lifestyles also dramatically changed over this transition as people began living outside of caves and increasingly experimented with food production. These changes brought them into contact with different microbes through agriculture, animal husbandry and their new built environments. Studying Pleistocene-era bacteria may yield insights into bacterial species and biosynthetic genes no longer associated with humans today, and perhaps even microbes that have gone extinct.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/JfX06NINZpk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Changes in human lifestyles changed our genomes.</span></figcaption>
</figure>
<p>While the amount of data collected by scientists on biological organisms has exponentially increased over the past few decades, the <a href="https://theconversation.com/antibiotic-resistance-is-at-a-crisis-point-government-support-for-academia-and-big-pharma-to-find-new-drugs-could-help-defeat-superbugs-169443">number of new antibiotics has stagnated</a>. This is particularly problematic when bacteria are able to evade existing antibiotic treatments faster than researchers can develop new ones. </p>
<p>By reconstructing microbial genomes from archaeological samples, scientists can tap into the hidden diversity of natural products that would have otherwise been lost over time, increasing the number of potential sources from which they can discover new drugs.</p>
<h2>Scaling up ancient molecules</h2>
<p>Our study has shown that it is possible to access natural products from the past. To tap into the vast diversity of chemical compounds encoded in ancient DNA, we now need to streamline our methodology to be less labor-intensive. </p>
<p>We are currently optimizing and automating our process to identify biosynthetic genes in ancient DNA more quickly and reliably. We are also implementing robotic liquid handling systems to complete the time-consuming pipetting and bacterial cultivation steps in our methods. Our goal is to scale up the process to be able to translate a vast amount of data on ancient microbes into the discovery of new therapeutic agents. </p>
<p>Although we can recreate ancient molecules, their biological and ecological roles are difficult to decipher. Since the bacteria that originally produced these compounds no longer exist, we cannot culture or genetically manipulate them. Further study will need to rely on similar bacteria that can be found today. Whether or not the functions of these compounds have remained the same in the modern relatives of ancient microbes remains to be tested. Although the original functions of these compounds for ancient microbes may be unknown, they still have the potential to be repurposed to treat modern diseases.</p>
<p>Ultimately, we aim to shed new light on microbial evolution and fight the current antibiotic crisis by providing a new time axis for antibiotic discovery.</p><img src="https://counter.theconversation.com/content/204888/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Christina Warinner receives funding from the Werner Siemens Foundation, the Francis Goelet Charitable Trust, the European Research Council, the United States National Science Foundation, and the Deutsche Forschungsgemeinschaft. She is affiliated with the Max Planck Institute for Evolutionary Anthropology, the Leibniz Institute of Natural Product Research and Infection Biology (Leibniz-HKI), and the Biological Faculty of Friedrich Schiller University Jena. </span></em></p><p class="fine-print"><em><span>Alexander Hübner receives funding from the Werner Siemens Foundation, the European Research Council, and the Deutsche Forschungsgemeinschaft. He is affiliated with with the Leibniz Institute of Natural Product Research and Infection Biology (Leibniz-HKI).</span></em></p><p class="fine-print"><em><span>Pierre Stallforth receives funding from the Werner Siemens Foundation, the Deutsche Forschungsgemeinschaft, and the Leibniz Association. He is affiliated with with the Leibniz Institute of Natural Product Research and Infection Biology (Leibniz-HKI) and the Friedrich Schiller University, Jena, Germany.</span></em></p>Ancient microbes likely produced natural products their descendants today do not. Tapping into this lost chemical diversity could offer a potential source of new drugs.Christina Warinner, Associate Professor of Anthropology, Harvard UniversityAlexander Hübner, Postdoctoral Researcher in Archaeogenetics, Max Planck Institute for Evolutionary AnthropologyPierre Stallforth, Professor of Bioorganic Chemistry and Paleobiotechnology, Friedrich-Schiller-Universität JenaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1875592022-09-06T12:37:31Z2022-09-06T12:37:31ZHuman skin stood up better to the sun before there were sunscreens and parasols – an anthropologist explains why<figure><img src="https://images.theconversation.com/files/480836/original/file-20220824-4026-m7s9pf.jpg?ixlib=rb-1.1.0&rect=663%2C34%2C5087%2C3794&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The sun’s rays often feel good on your skin, but can cause serious damage.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/close-up-of-woman-against-sky-during-sunset-royalty-free-image/1340270649">Maksim Chernyshev/EyeEm via Getty Images</a></span></figcaption></figure><p>Human beings have a conflicted relationship with the sun. People love sunshine, but then get hot. Sweat gets in your eyes. Then there are all the protective rituals: the sunscreen, the hats, the sunglasses. If you stay out too long or haven’t taken sufficient precautions, your skin lets us you know with an angry sunburn. First the heat, then the pain, then the remorse.</p>
<p>Were people always this obsessed with what the sun would do to their bodies? <a href="https://scholar.google.com/citations?user=NIAvKr8AAAAJ&hl=en&oi=ao">As a biological anthropologist</a> who has studied primates’ adaptations to the environment, I can tell you the short answer is “no,” and they didn’t need to be. For eons, skin stood up to the sun.</p>
<h2>Skin, between you and the world</h2>
<p>Human beings evolved under the sun. Sunlight was a constant in people’s lives, warming and guiding them through the days and seasons. <em>Homo sapiens</em> spent the bulk of our prehistory and history outside, mostly naked. Skin was the primary interface between our ancestors’ bodies and the world.</p>
<p>Human skin was adapted to whatever conditions it found itself in. People took shelter, when they could find it, in caves and rock shelters, and got pretty good at making portable shelters from wood, animal skins and other gathered materials. At night, they huddled together and probably covered themselves with fur “blankets.” But during the active daylight hours, people were outdoors and their mostly bare skin was what they had.</p>
<p>During a person’s lifetime, <a href="https://medlineplus.gov/ency/anatomyvideos/000125.htm">skin responds to routine exposure to the sun</a> in many ways. The surface layer of the skin – the epidermis – <a href="https://newsinhealth.nih.gov/2014/07/sun-skin">becomes thicker by adding more layers of cells</a>. For most people, the skin becomes gradually darker as specialized cells kick into action to produce a <a href="https://my.clevelandclinic.org/health/body/22615-melanin">protective pigment called eumelanin</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/480838/original/file-20220824-12-e8zgi6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="cross-sectional diagram of skin's layers with sunlight hitting the surface and showing increased production of melanin" src="https://images.theconversation.com/files/480838/original/file-20220824-12-e8zgi6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/480838/original/file-20220824-12-e8zgi6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/480838/original/file-20220824-12-e8zgi6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/480838/original/file-20220824-12-e8zgi6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/480838/original/file-20220824-12-e8zgi6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/480838/original/file-20220824-12-e8zgi6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/480838/original/file-20220824-12-e8zgi6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Exposure to the sun’s rays triggers production of more protective eumelanin, which also darkens the skin’s appearance.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/tanning-process-skin-human-anatomy-royalty-free-illustration/645165034">ttsz/iStock via Getty Images Plus</a></span>
</figcaption>
</figure>
<p>This remarkable molecule absorbs most visible light, causing it to look very dark brown, almost black. Eumelanin also absorbs damaging ultraviolet radiation. Depending on their genetics, people produce different amounts of eumelanin. Some have a lot and are able to produce a lot more when their skin is exposed to sun; others have less to start out with and produce less when their skin is exposed.</p>
<p><a href="https://scholar.google.com/citations?user=NIAvKr8AAAAJ&hl=en&oi=ao">My research on</a> <a href="https://doi.org/10.1111/pcmr.12976">the evolution of human skin pigmentation</a> has shown that the skin color of people in prehistory was tuned to local environmental conditions, primarily to local levels of ultraviolet light. People who lived under strong UV light – like you’d find near the equator – year in and year out had darkly pigmented and highly tannable skin capable of making a lot of eumelanin. People who lived under weaker and more seasonal UV levels – like you’d find in much of northern Europe and northern Asia – had lighter skin that had only limited abilities to produce protective pigment.</p>
<p>With only their feet to carry them, our distant ancestors didn’t move around much during their lives. Their skin adapted to subtle, seasonal changes in sunlight and UV conditions by producing more eumelanin and becoming darker in the summer and then losing some pigment in the fall and winter when the sun wasn’t so strong. Even for people with lightly pigmented skin, painful sunburns would have been exceedingly rare because there was never a sudden shock of strong sun exposure. Rather, as the sun strengthened during spring, the top layer of their skin would have gotten <a href="https://doi.org/10.1007/978-3-540-89656-2_60">gradually thicker over weeks and months of sun exposure</a>.</p>
<p>This is not to say that the skin would have been undamaged by today’s standards: Dermatologists would be appalled by the leathery and wrinkled appearance of the sun-exposed skin of our ancestors. Skin color, like the levels of sun itself, changed with the seasons and skin quickly showed its age. This is still the case for people who live traditional, mostly outdoor, lives in many parts of the world.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/479980/original/file-20220818-27-79ac87.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="a squatting old man with weathered skin" src="https://images.theconversation.com/files/479980/original/file-20220818-27-79ac87.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/479980/original/file-20220818-27-79ac87.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/479980/original/file-20220818-27-79ac87.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/479980/original/file-20220818-27-79ac87.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/479980/original/file-20220818-27-79ac87.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/479980/original/file-20220818-27-79ac87.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/479980/original/file-20220818-27-79ac87.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Chronic unprotected sun exposure can damage skin, with effects that look like those on this farmer in India.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:2020_Indian_farmers%27_protest_-_old_man_sitting.jpg">Randeep Maddoke/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>There is no preserved skin from thousands of years ago for scientists to study, but we can infer from the effects of sun exposure on modern people that the damage was similar. <a href="https://doi.org/10.1111/j.1365-2133.2009.09565.x">Chronic sun exposure</a> <a href="https://doi.org/10.1016/S1011-1344(01)00198-1">can lead to skin cancer</a>, but rarely of the variety – <a href="https://doi.org/10.1016/j.bjps.2006.05.008">melanoma</a> – that would cause death during reproductive age.</p>
<h2>Indoor living changed skin</h2>
<p>Until around 10,000 years ago – a drop in the bucket of evolutionary history – human beings made their living by <a href="https://www.history.com/topics/pre-history/hunter-gatherers">gathering foods, hunting and fishing</a>. Humanity’s relationship with the sun and sunlight changed a lot after people started to settle down and live in permanent settlements. <a href="https://www.smithsonianmag.com/history/the-seeds-of-civilization-78015429/">Farming and food storage</a> were associated with the development of immovable buildings. By around 6000 B.C. many people throughout the world were spending more time in walled settlements, and more time indoors.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/480840/original/file-20220824-4729-j9lpxl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="line drawing of royal bearded man followed by two smaller men with parasol and fly whisk" src="https://images.theconversation.com/files/480840/original/file-20220824-4729-j9lpxl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/480840/original/file-20220824-4729-j9lpxl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=1019&fit=crop&dpr=1 600w, https://images.theconversation.com/files/480840/original/file-20220824-4729-j9lpxl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=1019&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/480840/original/file-20220824-4729-j9lpxl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=1019&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/480840/original/file-20220824-4729-j9lpxl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1281&fit=crop&dpr=1 754w, https://images.theconversation.com/files/480840/original/file-20220824-4729-j9lpxl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1281&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/480840/original/file-20220824-4729-j9lpxl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1281&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Persian King Darius the Great, who lived more than 2,500 years ago, is portrayed being shielded from the sun.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/king-darius-the-great-followed-by-his-royalty-free-illustration/1367186124">Luisa Vallon Fumi/iStock via Getty Images Plus</a></span>
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<p>While most people still spent most of their time outside, some stayed indoors if they could. Many of them <a href="https://www.folkwear.com/blogs/news/historyoftheparasol">started protecting themselves from the sun</a> when they did go out. By at least 3000 B.C., a whole industry of sun protection grew up to create gear of all sorts – parasols, umbrellas, hats, tents and clothing – that would protect people from the discomfort and inevitable darkening of the skin associated with lengthy sun exposure. While some of these were originally reserved for nobility – like the parasols and umbrellas of ancient Egypt and China – these luxury items <a href="https://doi.org/10.1007/s11199-017-0785-4">began to be made</a> and <a href="https://doi.org/10.1080/17532523.2016.1281875">used more widely</a>.</p>
<p>In some places, people even developed <a href="https://doi.org/10.1371/journal.pone.0136090">protective pastes made out of minerals</a> and plant residues – <a href="https://doi.org/10.1111/jocd.14004">early versions of modern sunscreens</a> – to protect their exposed skin. Some, like the <a href="https://www.scmp.com/lifestyle/fashion-beauty/article/3100999/all-natural-sunscreen-and-beauty-product-thanaka-paste-has">thanaka paste used by people in Myanmar</a>, still persists today.</p>
<p>An important consequence of these practices in traditional agricultural societies was that people who spent most of their time indoors considered themselves privileged, and their lighter skin announced their status. A “farmer’s tan” was not glamorous: <a href="https://www.ucpress.edu/book/9780520283862/living-color">Sun-darkened skin was a penalty associated with hard outdoor work</a>, not the <a href="https://doi.org/10.2105/AJPH.2008.144352">badge of a leisurely vacation</a>. From Great Britain to China, Japan and India, suntanned skin became associated with a life of toil.</p>
<p>As people have moved around more and faster over longer distances in recent centuries, and spend more time indoors, their skin hasn’t caught up with their locations and lifestyles. Your levels of eumelanin probably aren’t perfectly adapted to the sun conditions where you live and so aren’t able to protect you the same way they might have your ancient ancestors.</p>
<p>Even if you’re naturally darkly pigmented or capable of tanning, everyone is susceptible to <a href="https://doi.org/10.1001/jamadermatol.2017.4201">damage caused by episodes of sun exposure</a>, especially after long breaks spent completely out of the sun. The “vacation effect” of sudden strong UV exposure is really bad because a sunburn signals damage to the skin that is never completely repaired. It’s like a bad debt that presents itself as prematurely aged or precancerous skin many years later. There is no healthy tan – a tan doesn’t protect you from further sun damage, it’s the sign of damage itself.</p>
<p>People may love the sun, but we’re not our ancestors. Humanity’s relationship with the sun has changed, and this means changing your behavior to save your skin.</p><img src="https://counter.theconversation.com/content/187559/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Nina G. Jablonski consults for L'Oreal and has received funding from the National Science Foundation, The Leakey Foundation, The Wenner-Gren Foundation, The Robert Wood Johnson Foundation, and The Rockefeller Foundation.</span></em></p>Our ancient ancestors didn’t have clothes or houses – but that constant exposure to the sun helped their skin protect itself from the worst sun damage.Nina G. Jablonski, Evan Pugh University Professor of Anthropology, Penn StateLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1781942022-03-09T16:23:14Z2022-03-09T16:23:14ZWe discovered how the largest dinosaurs walked – and it was more like hippos than elephants<figure><img src="https://images.theconversation.com/files/450781/original/file-20220308-21-iec6t4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/3d-rendering-walking-alamosaurus-1435978490">Kostiantyn Ivanyshen/shutterstock</a></span></figcaption></figure><p>While our knowledge of dinosaurs and other extinct animals has dramatically increased during the last couple of decades, their gaits – the order and timing of how animals move their legs – have remained a blind spot. </p>
<p>We are particularly interested in the giant long-necked sauropod dinosaurs, which include the largest animals that walked the earth, including such famous species as <em>Diplodocus</em>, <em>Brontosaurus</em> and <em>Brachiosaurus</em>. How did these giants move? What role did efficiency and stability play during their locomotion? </p>
<p>Those questions have not been easy to answer. The problem is that skeletons are the remains of deceased animals and don’t preserve motion. So reconstructing gaits based on fossilised bones can only indirectly provide clues, and are far from conclusive. </p>
<h2>Investigating gait from tracks</h2>
<p>As it happens, there is another type of fossil that records the activity of an animal when it was alive, and they are known as fossil trackways. But until now, extracting gait information about extinct dinosaurs from these footprints has proved difficult. </p>
<p><a href="https://www.google.co.uk/books/edition/Dinosaur_Tracks/EzI_DAAAQBAJ?hl=en&gbpv=1&dq=dinosaur+tracks+the+next+steps+stevens&pg=PA227&printsec=frontcover">A 2016 study</a> demonstrated that two animals of different sizes and using different gaits could produce identical track patterns. This means that to identify gait from the tracks we would need to know the trunk length of the animal (distance from hip to shoulder). Unfortunately it could not be accurately estimated from tracks so we were left with too many unknowns.</p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/a-social-species-newly-discovered-fossils-show-early-dinosaurs-lived-in-herds-170245">A social species? Newly discovered fossils show early dinosaurs lived in herds</a>
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<p>But one important aspect had not yet been taken into account – the variation along a set of tracks caused by small changes in speed. In <a href="https://www.cell.com/current-biology/fulltext/S0960-9822(22)00234-2">our new study</a>, we used this variation to present a new method to use tracks to work out which gait had been used. </p>
<p>Obviously the trunk length of an animal cannot change as it walks – so, we can therefore measure the trunk length from the tracks at many different points along it, while each time assuming a different gait. The gait which produces the most consistent trunk length along the tracks can be assumed to be the correct one.</p>
<figure class="align-center ">
<img alt="Large footprints on a track" src="https://images.theconversation.com/files/450776/original/file-20220308-17665-8bh42z.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/450776/original/file-20220308-17665-8bh42z.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/450776/original/file-20220308-17665-8bh42z.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/450776/original/file-20220308-17665-8bh42z.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/450776/original/file-20220308-17665-8bh42z.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/450776/original/file-20220308-17665-8bh42z.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/450776/original/file-20220308-17665-8bh42z.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Sauropod tracks from Utah.</span>
<span class="attribution"><span class="source">Jens Lallensack</span>, <span class="license">Author provided</span></span>
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</figure>
<p>It all made perfect mathematical sense. All we needed to do was make sure our new method worked when applied to the tracks of modern animals, including three dogs, two horses and an elephant. In each case, the method produced gratifyingly accurate estimates of the animals’ gaits.</p>
<h2>How dinosaurs moved</h2>
<p>So, for the first time we had developed a way to study gaits of the past. We applied the method to three fossilised tracks of giant sauropods from the Early Cretaceous period of Arkansas, in the US – the largest of which had footprint lengths of 85cm. </p>
<p>The results were really surprising. <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0078733">Previous studies</a> suggested that sauropods might have walked in a pace gait (similar to a camel) or a singlefoot walk (similar to a slow moving horse). But we expected that sauropod gaits would resemble those of elephants, as they are the largest land animals alive today. </p>
<p>Elephants employ lateral couplets gaits – they tend to move the fore and hind limb of the same body-side together, like in the animation below. They therefore fall in between the pace gait (the extreme of a lateral couplets gait where hind and fore limb of one body side move exactly in sync) and the singlefoot gait (where the time lag between all limb movements is exactly equal).</p>
<figure class="align-center ">
<img alt="Animation showing how animal legs move using a lateral couplet gait, where limbs of the same side move together" src="https://images.theconversation.com/files/450777/original/file-20220308-13-uti16o.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/450777/original/file-20220308-13-uti16o.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/450777/original/file-20220308-13-uti16o.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/450777/original/file-20220308-13-uti16o.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/450777/original/file-20220308-13-uti16o.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/450777/original/file-20220308-13-uti16o.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/450777/original/file-20220308-13-uti16o.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The lateral couplets gait, seen in animals such as elephants.</span>
<span class="attribution"><span class="source">Jens Lallensack</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Our new method, however, indicates that all three sauropods we studied via tracks had walked in a diagonal couplets gait, where they move the limbs of the opposite body-side together. The extreme in this gait is called a trot (the diagonal pair moves exactly in sync). So, to our surprise sauropods did the opposite of what we see in elephants. </p>
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<p>How can this difference be explained? Well, Cretaceous sauropods do differ from elephants in one important aspect – they are much wider. The tracks we studied are especially broad (or wide-gauged), with left and right tracks spaced well apart from each other. </p>
<p>Elephants, in contrast, set one foot almost in front of the other, forming a narrow path. This has consequences for the gait. An elephant only needs to shift its body mass slightly to one side in order to swing both legs of the other side forward together. A wide-gauged sauropod, however, would have needed to drastically sway its body towards one side to achieve the same. </p>
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Read more:
<a href="https://theconversation.com/dinosaur-embryo-discovery-rare-fossil-suggests-dinosaurs-had-similar-pre-hatching-posture-to-modern-birds-174040">Dinosaur embryo discovery: rare fossil suggests dinosaurs had similar pre-hatching posture to modern birds</a>
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<p>So, the diagonal couplets gait assured that the sauropods always had at least one foot on the ground on either side of the body, avoiding such swaying from left to right. Stability therefore seems to have played a major role in how the largest creatures ever to have roamed this planet walked.</p>
<p>Interestingly, almost all large modern mammals show very narrow tracks, in combination with lateral couplets gaits. But the wide-tracked hippopotamus, in contrast, uses a diagonal couplets gait (moving limbs of the opposite body side together) just as we estimated for wide-tracked sauropods. So while it’s easy to assume that because elephants are the largest animals on land today, large land animals of the past must have moved like them, it appears that this was not the case.</p><img src="https://counter.theconversation.com/content/178194/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Peter Falkingham works for Liverpool John Moores University, UK.</span></em></p><p class="fine-print"><em><span>Jens N. Lallensack receives funding from the German science foundation</span></em></p>Thanks to our new technique using fossilised tracks, we have been able to learn more about the locomotion of the largest creatures ever to have roamed this planet.Peter Falkingham, Reader in Vertebrate Biology, Liverpool John Moores UniversityJens N. Lallensack, Postdoctoral Research Fellow in Palaeontology, Liverpool John Moores UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1601522021-05-06T18:12:42Z2021-05-06T18:12:42ZNocturnal dinosaurs: Night vision and superb hearing in a small theropod suggest it was a moonlight predator<figure><img src="https://images.theconversation.com/files/398999/original/file-20210505-17-16fmhv4.png?ixlib=rb-1.1.0&rect=32%2C9%2C1511%2C788&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Fossils of _Shuvuuia deserti_ depict a small predatory creature with exceptional night vision and hearing.</span> <span class="attribution"><span class="source">Mick Ellison/American Natural History Museum</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>Today, barn owls, bats, leopards and many other animals rely on their keen senses to live and hunt under the dim light of stars. These <a href="https://doi.org/10.1086/702250">nighttime specialists avoid the competition of daylight hours</a>, hunting their prey under the cloak of darkness, often using a combination of night vision and acute hearing.</p>
<p>But was there nightlife 100 million years ago? In a world without owls or leopards, were dinosaurs working the night shift? If so, what senses did they use to find food and avoid predators in the darkness? To better understand the senses of the dinosaur ancestors of birds, <a href="https://scholar.google.com/citations?user=kHIW_0cAAAAJ&hl=en&oi=ao">our team</a> of <a href="https://scholar.google.com/citations?user=6qODxwoAAAAJ&hl=en&oi=ao">paleontologists</a> and <a href="https://scholar.google.com/citations?user=m_p_Lc0AAAAJ&hl=en&oi=ao">paleobiologists</a> scoured research papers and museum collections looking for fossils that preserved delicate eye and ear structures. And we found some. </p>
<p>Using scans of fossilized dinosaur skulls, in a paper <a href="https://science.sciencemag.org/content/372/6542/610?intcmp=trendmd-sci">published in the journal Science on May 6, 2021</a>, we describe the most convincing evidence to date for nocturnal dinosaurs. Two fossil species – <em>Haplocheirus sollers</em> and <em>Shuvuuia deserti</em> – likely had extremely good night vision. But our work also shows that <em>S. deserti</em> also had incredibly sensitive hearing similar to modern-day owls. This is the first time these two traits have been found in the same fossil, suggesting that this small, desert-dwelling dinosaur that lived in ancient Mongolia was probably a specialized night-hunter of insects and small mammals.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/399011/original/file-20210505-23-hnil4h.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An artistic reconstruction showing _S. deserti as a small, feathered bipedal dinosaur with an owlish face." src="https://images.theconversation.com/files/399011/original/file-20210505-23-hnil4h.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/399011/original/file-20210505-23-hnil4h.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=848&fit=crop&dpr=1 600w, https://images.theconversation.com/files/399011/original/file-20210505-23-hnil4h.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=848&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/399011/original/file-20210505-23-hnil4h.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=848&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/399011/original/file-20210505-23-hnil4h.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1066&fit=crop&dpr=1 754w, https://images.theconversation.com/files/399011/original/file-20210505-23-hnil4h.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1066&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/399011/original/file-20210505-23-hnil4h.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1066&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"><em>Shuvuuia deserti</em> had acute hearing and low-light vision that would have allowed it to hunt at night.</span>
<span class="attribution"><span class="source">Viktor Radermaker</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Looking to theropods</h2>
<p>By studying fossilized eye bones, one of us, Lars Schmitz, had previously found that some small predatory dinosaurs <a href="https://doi.org/10.1126/science.1200043">may have hunted at night</a>. Most of these potentially nocturnal hunters were theropods, the group of three-toed dinosaurs that includes <em>Tyrannosaurus rex</em> and modern birds. But to date, fossils for only <a href="https://doi.org/10.1126/science.1200043">12 theropod species included the eye structures</a> that can tell paleontologists about night vision.</p>
<p>Our team identified four more species of theropods with clues for their sense of vision – for a total of 16. We then looked for fossils that preserve the structures of the inner ear and found 17 species. Excitingly, for four species, we were able to get measurements for both eyes and ears.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/399012/original/file-20210505-23-usv75o.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A close up photo of the skull of _S. deserti_ showing a large eye socket." src="https://images.theconversation.com/files/399012/original/file-20210505-23-usv75o.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/399012/original/file-20210505-23-usv75o.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=378&fit=crop&dpr=1 600w, https://images.theconversation.com/files/399012/original/file-20210505-23-usv75o.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=378&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/399012/original/file-20210505-23-usv75o.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=378&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/399012/original/file-20210505-23-usv75o.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=475&fit=crop&dpr=1 754w, https://images.theconversation.com/files/399012/original/file-20210505-23-usv75o.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=475&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/399012/original/file-20210505-23-usv75o.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=475&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">The eye socket – and specifically the sclerical ring – of <em>S. deserti</em> shows an eye with a very large pupil capable of letting in large amounts of light.</span>
<span class="attribution"><span class="source">Mick Ellison/American Museum of Natural History</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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</figure>
<h2>Eye bones built for night vision</h2>
<p>Scleral ossicles are thin, rectangular bone plates that form a <a href="https://doi.org/10.1002/ar.24043">ring-like structure surrounding the pupils</a> of lizards as well as birds and their ancestors – dinosaurs. Scleral rings define the largest possible size of an animal’s pupil and can tell you how well that animal <a href="https://doi.org/10.1016/j.visres.2010.03.009">can see at night</a>. The larger the pupil compared to the size of the eye, the better a dinosaur could see in the dark.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/399017/original/file-20210505-19-1imtqg9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An owl skull with a cone like ring attached to the eye socket." src="https://images.theconversation.com/files/399017/original/file-20210505-19-1imtqg9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/399017/original/file-20210505-19-1imtqg9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=456&fit=crop&dpr=1 600w, https://images.theconversation.com/files/399017/original/file-20210505-19-1imtqg9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=456&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/399017/original/file-20210505-19-1imtqg9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=456&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/399017/original/file-20210505-19-1imtqg9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=573&fit=crop&dpr=1 754w, https://images.theconversation.com/files/399017/original/file-20210505-19-1imtqg9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=573&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/399017/original/file-20210505-19-1imtqg9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=573&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">This owl skull clearly shows the large scleral ring that helps animals see in darkness.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Bubo_virginianus_8zz.jpg#/media/File:Bubo_virginianus_8zz.jpg">David J. Stang/WikimediaCommons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Since the individual bony ossicles of these rings fell apart after these animals died more than 60 million years ago, our team made scans of the fossils and then digitally reconstructed the eyes. Of all the theropods we examined, <em>H. sollers</em> and <em>S. deserti</em> had some of the proportionally largest pupils.</p>
<p><em>S. deserti</em>‘s pupil made up more than half of its eye, very similar to night-vision specialists that live today like geckos and nightjars. Our team then compared the fossils to 55 living species of lizards and 367 species of birds with known day or night activity patterns. According to the statistical analyses our team performed, there is a very high chance – higher than 90% – that <em>H. sollers</em> and <em>S. deserti</em> were nocturnal.</p>
<p>But those were not the only two theropods our team looked at. Our analysis also found a few other likely nighttime specialists – such as <em>Megapnosaurus kayentakatae</em> – as well as daylight specialists like <em>Almas ukhaa</em>. But we also found some species – like <em>Velociraptor mongoliensis</em> – with eyesight seemingly adapted for medium light levels. This might suggest that they hunted around dawn or dusk.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/399020/original/file-20210505-19-62si2q.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two white plastic molds on a black background both with an elongated vertical base splitting into a 'y' shape at the top." src="https://images.theconversation.com/files/399020/original/file-20210505-19-62si2q.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/399020/original/file-20210505-19-62si2q.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/399020/original/file-20210505-19-62si2q.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/399020/original/file-20210505-19-62si2q.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/399020/original/file-20210505-19-62si2q.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/399020/original/file-20210505-19-62si2q.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/399020/original/file-20210505-19-62si2q.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Molds of the inner ear canal from a barn owl (left) and <em>S. deserti</em> (right) are almost identical, suggesting that the small dinosaur had incredible hearing.</span>
<span class="attribution"><span class="source">Shivan Parusnath/Wits University</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Incredible ears of a dinosaur</h2>
<p>In today’s nocturnal animals, <a href="https://doi.org/10.1002/bies.201600006">hearing can be as important as keen eyesight</a>. To figure out how well these extinct dinosaurs could hear, we scanned the skulls of 17 fossil theropods to decipher the structure of their inner ears and then compared our scans to the ears of modern animals.</p>
<p>All vertebrates have a tube-like canal called the cochlea deep in their inner ear. Studies of living mammals and birds show that the longer this canal, the <a href="https://doi.org/10.1098/rspb.2008.1390">wider the range of frequencies an animal can hear</a> and the better they can hear <a href="https://doi.org/10.1098/rspb.2008.1390">very faint sounds</a>.</p>
<p>Our scans showed that <em>S. deserti</em> had an extremely elongated inner ear canal for its size – also similar to that of the living barn owl and proportionally much longer than all of the other 88 living bird species we analyzed for comparison. Based on our measurements, among dinosaurs, we found that predators had generally better hearing than herbivores. Several predators – including <em>V. mongoliensis</em> – also had moderately elongated inner ears, but none rivaled <em>S. deserti</em>’s. </p>
<h2>The life of a nocturnal dinosaur</h2>
<p>By studying the sensory abilities of dinosaurs, paleontologists like us not only are learning what species roamed the night, but can also begin to infer how these dinosaurs lived and shared resources.</p>
<p><a href="https://doi.org/10.1126/science.abe7941"><em>S. deserti</em> had extreme night vision and sensitive hearing</a>, and this little dinosaur probably used its incredible senses to hunt prey at night. It could likely hear and follow rustling from a distance before visually detecting its prey and digging it up from the ground with its short single-clawed arms. In the dry, desert-like habitats of millions of years ago, it might have been an evolutionary advantage to be active in the cooler temperatures of the night. </p>
<p>But according to our analysis, <em>S. deserti</em> wasn’t the only dinosaur active at night. Other dinosaurs like <em>V. mongoliensis</em> and the plant-eating <em>Protoceratops mongoliensis</em> both lived in the same habitat and had some level of night vision.</p>
<p>Paleontologists currently do not know the full suite of animals that shared <em>S. deserti</em>’s extreme nocturnal lifestyle in the ancient deserts of Mongolia – it is rare to find fossils with the right bones intact that allow paleontologists to investigate their senses. However, the presence of a specialized night forager highlights that much like today, some dinosaurs avoided the dangers and competition of daylight hours and roamed under the stars.</p>
<p>[<em>Get the best of The Conversation, every weekend.</em> <a href="https://theconversation.com/us/newsletters/weekly-highlights-61?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=weeklybest">Sign up for our weekly newsletter</a>.]</p><img src="https://counter.theconversation.com/content/160152/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jonah Choiniere receives funding from the National Research Foundation of South Africa. </span></em></p><p class="fine-print"><em><span>Roger Benson receives funding from the European Research Council, National Environments Research Council and Leverhulme Trust. </span></em></p><p class="fine-print"><em><span>Lars Schmitz does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>By looking at the eye bones and ear canals of extinct dinosaurs, researchers show that a small ancient predator likely hunted at night and had senses as good as a modern barn owl.Lars Schmitz, Associate Professor of Biology, Scripps CollegeJonah Choiniere, Professor of Dinosaur Paleontology, University of the WitwatersrandRoger Benson, Professor of Palaeobiology, University of OxfordLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1589052021-04-15T10:59:25Z2021-04-15T10:59:25ZDinosaurs: from giant reptiles to warm-blooded, feathered creatures, how our understanding of what they looked like has changed – podcast<figure><img src="https://images.theconversation.com/files/394992/original/file-20210414-14-1qjmil2.jpg?ixlib=rb-1.1.0&rect=14%2C40%2C538%2C404&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Kulindadromeus: more evidence is emerging of feathered dinosaurs. </span> <span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Kulindadromeus#/media/File:Kulindadromeus_NT_small.jpg">Nobu Tamura via Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>In this episode of <a href="https://theconversation.com/uk/topics/the-conversation-weekly-98901">The Conversation Weekly</a> podcast, we look at how new discoveries are changing our understanding of what dinosaurs looked like and are helping to shed light on bigger questions about evolution. And after Israel’s fourth election in two years ended in another political stalemate, we speak to a foreign policy expert on what this could mean for the Middle East. </p>
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<p><iframe id="tc-infographic-561" class="tc-infographic" height="100" src="https://cdn.theconversation.com/infographics/561/4fbbd099d631750693d02bac632430b71b37cd5f/site/index.html" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>Ever since palaeontologists started classifying fossils and bones as dinosaurs in the early 19th century, artists have been using them to try to imagine what dinosaurs looked like. Some of these depictions, we now know, are pretty inaccurate, such as the notorious <a href="https://cpdinosaurs.org/visit/what-are-crystal-palace-dinosaurs/">Victorian sculptures of dinosaurs</a> still on display in Crystal Palace Park in London. </p>
<p>But, however much Hollywood may have instilled a certain vision of dinosaurs into our minds in recent decades, we’re still a long way off having all the answers about what dinosaurs actually looked like. To find out more about what new evidence is emerging and how our dinosaur imaginings have changed, we speak to two palaeontologists. </p>
<p>Maria McNamara, professor of palaeobiology at University College Cork in Ireland, tells us about the, at times controversial, history of <a href="https://theconversation.com/the-mystery-of-feather-origins-how-fluffy-pterosaurs-have-reignited-debate-149119">feathered dinosaurs</a>. She explains how the discovery of melanin in fossils is providing a picture of the colours of these feathers and what they may have been used for. “There are dinosaurs where we’re pretty sure that feathers were being used for communication,” explains McNamara. </p>
<hr>
<p>
<em>
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Read more:
<a href="https://theconversation.com/prehistoric-pigments-reveal-how-melanin-has-shaped-bird-and-mammal-evolution-154899">Prehistoric pigments reveal how melanin has shaped bird and mammal evolution</a>
</strong>
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<p>And Nicolas Campione, senior lecturer in paleaobiology at the University of New England in Australia, tells us the two main techniques palaeontologists have used for estimating the size of dinosaurs and <a href="https://theconversation.com/how-do-you-weigh-a-dinosaur-there-are-two-ways-and-it-turns-out-theyre-both-right-144874">how he tested their accuracy</a>. He also explains how understanding the size of dinosaurs can tell us more about their evolution. “The first dinosaurs start off at one body size, the size of a large dog, and then they radiate very quickly so that within the first ten or so million years you already reached most of the size range that dinosaurs would continue to have the rest of their evolutionary history,” says Campione.</p>
<p>And in our second story, we head to Israel, where coalition negotiations are continuing following elections on March 23. The prime minister, Benjamin Netanyahu who is <a href="https://www.nytimes.com/2021/04/05/world/middleeast/netanyahu-on-trial-israel.html">on trial for corruption,</a> has been invited to try and form a new government. Whatever happens next will have ramifications for Israel’s foreign policy, which is <a href="https://www.cambridge.org/core/books/israeli-foreign-policy-since-the-end-of-the-cold-war/6E16D0C5973C8024560471A1F8530329">closely tied with domestic politics</a>. Amnon Aran, a senior lecturer in international politics of the Middle East, at City, University of London, talks us through how history could inform what happens next, and what the foreign policy stakes are for whoever takes the reins of the next Israeli government. </p>
<p>And Eva Catalán, culture editor at The Conversation in Spain, gives us her recommended reads. </p>
<p>The Conversation Weekly is produced by Mend Mariwany and Gemma Ware, with sound design by Eloise Stevens. Our theme music is by Neeta Sarl. You can find us on Twitter <a href="https://twitter.com/TC_Audio">@TC_Audio</a>, on Instagram at <a href="https://www.instagram.com/theconversationdotcom/?hl=en">theconversationdotcom</a>. or via email on podcast@theconversation.com. You can also sign up to <a href="https://theconversation.com/newsletter?utm_campaign=PodcastTCWeekly&utm_content=newsletter&utm_source=podcast">The Conversation’s free daily email here</a>.</p>
<p>A transcript of this episode <a href="https://theconversation.com/dinosaurs-how-our-understanding-of-what-they-looked-like-keeps-changing-158937">is available here.</a></p>
<p>News clips in this episode are from <a href="https://www.youtube.com/watch?v=Ut8vR8xee7o">euronews</a>, <a href="https://www.youtube.com/watch?v=SY8pdQMMRzI">DW News</a>, <a href="https://www.youtube.com/watch?v=6EkaLMMc614">Al Jazeera News</a>, <a href="https://www.youtube.com/watch?v=3eXreXGmPPI">ILTV Israel News</a>, <a href="https://www.youtube.com/watch?v=VMfxNi0mqiY">i24News</a>, <a href="https://www.youtube.com/watch?v=zA8NN4wC1_c">CBC News</a>, <a href="https://www.youtube.com/watch?v=Wd4EykJ-IjM">Fox News</a> and <a href="https://www.youtube.com/watch?v=FFBdfzR6cjY">WION News</a>. </p>
<p><em>You can listen to The Conversation Weekly via any of the apps listed above, our <a href="https://feeds.acast.com/public/shows/60087127b9687759d637bade">RSS feed</a>, or find out how else to <a href="https://theconversation.com/how-to-listen-to-the-conversations-podcasts-154131">listen here</a>.</em></p><img src="https://counter.theconversation.com/content/158905/count.gif" alt="The Conversation" width="1" height="1" />
Plus, what Israel’s latest election could mean for its foreign policy. Listen to episode 11 of The Conversation Weekly podcast.Gemma Ware, Head of AudioDaniel Merino, Associate Breaking News Editor and Co-Host of The Conversation Weekly PodcastLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1265312019-11-11T12:07:32Z2019-11-11T12:07:32ZThe mysterious ‘Tully Monster’ fossil just got more mysterious<figure><img src="https://images.theconversation.com/files/300639/original/file-20191107-10940-1uhlvb.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artist's impression of _Tullimonstrum_.</span> <span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Tullimonstrum#/media/File:Tullimonstrum.png">PaleoEquii/Wikipedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Every now and again, scientists discover fossils that are <a href="https://theconversation.com/five-bizarre-fossil-discoveries-that-got-scientists-excited-44750">so bizarre</a> they defy classification, their body plans unlike any other living animals or plants. <em>Tullimonstrum</em> (also known as the Tully Monster), a 300m-year-old fossil discovered in the Mazon Creek fossil beds in Illinois, US, is one such creature.</p>
<p>At first glance, Tully looks superficially slug-like. But where you would expect its mouth to be, the creature has a long thin appendage ending in what looks like a pair of grasping claws. Then there are its eyes, which protrude outward from its body on stalks.</p>
<p>Tully is so strange that scientists have even been unable to agree on whether it is a vertebrate (with a backbone, like mammals, birds, reptiles and fish) or an invertebrate (without a backbone, like insects, crustaceans, octopuses and all other animals). In 2016, a group of scientists claimed to have <a href="https://www.scientificamerican.com/article/tully-monster-mystery-solved-scientists-say/">solved the mystery</a> of Tully, providing the strongest evidence yet that it was a vertebrate. But my colleagues and I have conducted a new study that calls this conclusion into question, meaning this monster is as mysterious as ever.</p>
<p>The Tully Monster was <a href="http://isgs.illinois.edu/outreach/geology-resources/illinois-state-fossil-tullimonstrum-gregarium">originally discovered</a> in the 1950s by a fossil collector named Francis Tully. Ever since its discovery scientists have puzzled over which group of modern animals Tully belongs to. The enigma of Tully’s true evolutionary relationships has added to its popularity, ultimately leading it to become the state fossil of Illinois.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/300643/original/file-20191107-10952-dbhywm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/300643/original/file-20191107-10952-dbhywm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=335&fit=crop&dpr=1 600w, https://images.theconversation.com/files/300643/original/file-20191107-10952-dbhywm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=335&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/300643/original/file-20191107-10952-dbhywm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=335&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/300643/original/file-20191107-10952-dbhywm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=421&fit=crop&dpr=1 754w, https://images.theconversation.com/files/300643/original/file-20191107-10952-dbhywm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=421&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/300643/original/file-20191107-10952-dbhywm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=421&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The <em>Tullimonstrum</em> fossil.</span>
<span class="attribution"><span class="source">Ghedoghedo/Wikimedia</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>There have been <a href="https://www.elsevier.com/books/mazon-creek-fossils/nitecki/978-0-12-519650-5">many attempts</a> to classify the <a href="https://www.biodiversitylibrary.org/item/25103#page/11/mode/1up">Tully Monster</a>. The majority of these studies have focused on the appearance of some of its more prominent features. These include a linear feature in the fossil interpreted as evidence of a gut, the light and dark banding of the fossil and the peculiar grasping claws of its mouth. The body plan of the Tully Monster is so unusual in it’s entirety that it will greatly expand the diversity of of whatever group it ultimately belongs to, changing the way we think about that group of animals.</p>
<p><a href="https://www.nature.com/articles/nature17647?draft=journal&proof=trueIn">The 2016 research</a> argued the animal should be grouped with vertebrates because its eyes contain pigment granules called melanosomes, which are arranged by shape and size in the same way as those in vertebrate eyes. But our research shows that the eyes of some invertebrates such as octopus and squid also contain melanosomes partitioned by shape and size in a similar way to Tully’s eyes, and that these an also be preserved in fossils.</p>
<h2>Particle accelerator research</h2>
<p>To do this, we used a type of particle accelerator called a synchrotron radiation lightsource located at Stanford University in California. This allowed us to explore the chemical makeup of samples from fossils and from animals living today. The synchrotron bombards specimens with intense bursts of radiation to “excite” the elements within them. When excited, each element releases X-rays with a specific signature. By detecting the emitted X-ray signatures, we can tell what elements were excited and ultimately what the specimen we’re interested in is made of.</p>
<p>First we found that melanosomes from the eyes of modern vertebrates have a higher ratio of zinc to copper than the modern invertebrates we studied. To our surprise, we then found the same pattern could be seen in fossilised vertebrates and invertebrates found at Mazon Creek.</p>
<p>We then analysed the chemistry of Tully’s eyes and the ratio of zinc to copper was more similar to that of invertebrates than vertebrates. This suggests the animal may not have been a vertebrate, contradicting previous efforts to classify it.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/300644/original/file-20191107-10952-1gejyu9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/300644/original/file-20191107-10952-1gejyu9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/300644/original/file-20191107-10952-1gejyu9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/300644/original/file-20191107-10952-1gejyu9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/300644/original/file-20191107-10952-1gejyu9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/300644/original/file-20191107-10952-1gejyu9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/300644/original/file-20191107-10952-1gejyu9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Another possible look for the Tully Monster.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Tullimonstrum_NT_small.jpg">Nobu Tamura/Wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>We also found that Tully’s eyes contain different type of copper to that found in vertebrate eyes. But the copper also wasn’t identical to that in the invertebrates we studied. So while our work adds weight to the idea that Tully is not a vertebrate, it doesn’t clearly identify it as an invertebrate either.</p>
<p>Where do we go from here? A broader analysis of the chemistry of melanosomes and other pigments in the eyes of a wider range of invertebrates would be a good next step. This may help to further narrow down the group of animals to which Tully belongs.</p>
<p>Ultimately the riddle of what kind of creature the Tully Monster is continues. But our research demonstrates how studying fossils at the chemical and molecular levels can play an important part in figuring out the identity of this and other enigmatic creature.</p><img src="https://counter.theconversation.com/content/126531/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris Rogers does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Scientists claimed they knew what this bizarre creature was – our evidence suggests the question is still open.Chris Rogers, Postdoctoral Researcher in Palaeobiology, University College CorkLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1140542019-03-22T18:54:02Z2019-03-22T18:54:02ZExquisite fossil finds shed new light on the ‘Cambrian explosion’, when oceans first filled with complex animal life<figure><img src="https://images.theconversation.com/files/265296/original/file-20190322-36270-5zj4ip.jpg?ixlib=rb-1.1.0&rect=2382%2C0%2C4279%2C2392&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Dotted Yeti / shutterstock</span></span></figcaption></figure><p>The most recent 12% of time on Earth is a striking anomaly when compared with the great bulk of our planet’s evolution. After 3 billion years or more of Earth as a microbial world, cells found ways to grow and assemble in their millions to build eyes, guts, muscles, nerve systems with brains, skeletons and the rest of the complex structures that form the mobile, sentient, marvellously various animals that fill our now familiar world. </p>
<p>The speed of this transition, seen by geologists in the sudden appearance of complex fossils such as trilobites in layers of rock, seemed so shockingly abrupt that it amazed and worried even <a href="https://www.wired.com/2009/09/did-the-cambrian-really-give-darwin-nightmares/">Charles Darwin</a>. As this flowering of complex multicellular life is used to mark the beginning of the Cambrian Period of Earth time, 541m years ago, it has long been called the “<a href="https://theconversation.com/uk/topics/cambrian-explosion-7159">Cambrian explosion</a>”.</p>
<p>We now know it was not quite so abrupt. The evolution actually took place in distinct stages over more than 30m years – the pioneering geologist Preston Cloud called it “the Cambrian eruption”.</p>
<p>The period has, somewhat mysteriously, left behind more than its fair share of amazing fossil localities called “Lagerstätten”, where not only hard skeletons but soft and delicate tissues are preserved, to give a much clearer window on the totality of life than the usual fragments of shell and bone. The classic in this respect was long the Burgess Shale, high up on Mount Stephen in British Columbia, Canada, and mined for its wondrous fossils for more than a century. In the past three decades it has been joined by China’s <a href="https://theconversation.com/evolution-timeframes-get-a-rethink-after-scientists-take-a-closer-look-at-earths-first-animals-100834">Chengjiang deposits</a>. </p>
<p>Together these have given a detailed picture from near the dawn of animal life in the marine realm (the land, then, was still largely barren): a wealth of arthropods, worms, lamp shells, sponges, chordates, and even some animals that still <a href="http://www.sci-news.com/paleontology/science-nidelric-pugio-fossil-spiny-marine-animal-china-02332.html">defy biological assignment</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/265299/original/file-20190322-36270-1bpg066.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/265299/original/file-20190322-36270-1bpg066.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/265299/original/file-20190322-36270-1bpg066.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/265299/original/file-20190322-36270-1bpg066.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/265299/original/file-20190322-36270-1bpg066.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/265299/original/file-20190322-36270-1bpg066.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/265299/original/file-20190322-36270-1bpg066.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/265299/original/file-20190322-36270-1bpg066.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Chinese scientists digging up fossils at the Qingjiang site.</span>
<span class="attribution"><a class="source" href="http://science.sciencemag.org/cgi/doi/10.1126/science.aau8800">Dong King Fu</a></span>
</figcaption>
</figure>
<p>Now another Cambrian Lagerstätte has turned up – and the first results, just published in <a href="http://science.sciencemag.org/cgi/doi/10.1126/science.aau8800">Science</a>, suggest that it may rival those of the Burgess Shale and Chengjiang. It is also in China, in Qingjiang in Hubei province, and is about the same age as the Chengjiang, some 518m years old, and so in the early part of the Cambrian Period. Indeed, it formed on the same general stretch of continental shelf sea as the Chengjiang fossils, about 1,000km away, and seemingly in somewhat deeper waters. What is surprising is that not only are the fossils just as exquisite, but they represent quite different animal communities. The Cambrian seas were clearly more diverse than thought, even in those early days.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/265193/original/file-20190321-93032-1xh48w1.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/265193/original/file-20190321-93032-1xh48w1.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/265193/original/file-20190321-93032-1xh48w1.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=926&fit=crop&dpr=1 600w, https://images.theconversation.com/files/265193/original/file-20190321-93032-1xh48w1.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=926&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/265193/original/file-20190321-93032-1xh48w1.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=926&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/265193/original/file-20190321-93032-1xh48w1.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1164&fit=crop&dpr=1 754w, https://images.theconversation.com/files/265193/original/file-20190321-93032-1xh48w1.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1164&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/265193/original/file-20190321-93032-1xh48w1.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1164&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A 514m year old jellyfish – with tentacles still attached.</span>
<span class="attribution"><a class="source" href="http://science.sciencemag.org/cgi/doi/10.1126/science.aau8800">Fu et al</a></span>
</figcaption>
</figure>
<p>Although the Qingjiang fossils do include many worms, arthropods and sponges, they also are prolific in animals possessing the most delicate and translucent of tissues, such as jellyfish, here preserved with mouths and tentacles, and their distant relatives “comb jellies”. These are rare in the Burgess Shale and Chengjiang deposits, but among the Qingjiang fossils there are many astounding examples, flattened on the shale surfaces and preserving fine details of these softest of anatomies. </p>
<p>The comb jellies may be the <a href="https://cosmosmagazine.com/biology/the-first-animals-were-comb-jellies-genetic-study-finds">earliest form of animal</a> – a title that they currently contest with the <a href="https://www.nature.com/articles/s41559-018-0676-2">sponges</a>. Both these kinds of animal are preserved here, in numbers and fidelity that may help resolve the dispute.</p>
<p>Other strange and wonderful animals appear in the Qingjiang strata, and represent curious and perhaps profound trends in evolution. There are kinorhynchs, for example – these are the “mud dragons”, animals that are today obscure because they are part of the “meiofauna”, those tiny creatures that live between grains of sediment on the sea floor. </p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/265300/original/file-20190322-36279-xhkwgg.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/265300/original/file-20190322-36279-xhkwgg.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/265300/original/file-20190322-36279-xhkwgg.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=925&fit=crop&dpr=1 600w, https://images.theconversation.com/files/265300/original/file-20190322-36279-xhkwgg.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=925&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/265300/original/file-20190322-36279-xhkwgg.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=925&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/265300/original/file-20190322-36279-xhkwgg.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1163&fit=crop&dpr=1 754w, https://images.theconversation.com/files/265300/original/file-20190322-36279-xhkwgg.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1163&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/265300/original/file-20190322-36279-xhkwgg.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1163&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A possible kinorhynch, with segmented body armoured with spines.</span>
<span class="attribution"><span class="source">Fu et al / Science</span></span>
</figcaption>
</figure>
<p>Here, three new fossil forms have been found, some up to 4cm long, rather than the contemporary sub-millimetre size. These Cambrian giants suggest that some of today’s meiofauna started off “normally” sized, and then became miniaturised – for good.</p>
<p>It is a true cornucopia. How did it form? The same kind of quickfire preservation process is mooted as for the Burgess Shale and the Chengjiang fossils: the animals were caught up in mud slurries, and carried down to deep, oxygen-starved parts of the sea floor to be rapidly buried in the stifling mud. It makes sense – but then such conditions and processes persisted long after the Cambrian, and yet were rarely associated with such bonanza fossil finds. There is much that remains mysterious about the dawn of life as we know it – but the Qingjiang fossils, as we study them more, will slowly shed light on these enigmas.</p><img src="https://counter.theconversation.com/content/114054/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Exceptionally well preserved 500m year old fossils show Cambrian seas were more diverse than scientists had thought.Jan Zalasiewicz, Professor of Palaeobiology, University of LeicesterMark Williams, Professor of Palaeobiology, University of LeicesterLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1017732018-08-22T10:37:09Z2018-08-22T10:37:09ZWhat makes some species more likely to go extinct?<figure><img src="https://images.theconversation.com/files/232772/original/file-20180820-30587-1060no3.jpg?ixlib=rb-1.1.0&rect=209%2C0%2C2286%2C1497&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Dinosaurs had some bad luck, but sooner or later extinction comes for all of us.</span> <span class="attribution"><a class="source" href="https://unsplash.com/photos/jSGBfrmEQnQ">rawpixel/Unsplash.com</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>Though they say “‘tis impossible to be sure of <a href="http://freakonomics.com/2011/02/17/quotes-uncovered-death-and-taxes/">anything but death and taxes</a>,” a bit of financial chicanery may get you out of paying the taxman. But no amount of trickery will stop the inevitability of death. Death is the inescapable endpoint of life.</p>
<p>And this is as true for species as it is for individuals. Estimates suggest <a href="https://doi.org/10.1006/jtbi.1997.0508">99.99 percent of all species that have ever lived are now extinct</a>. All species that exist today – including human beings – will invariably go extinct at some point. </p>
<p><a href="https://scholar.google.com/citations?user=1u3axhQAAAAJ&hl=en&oi=ao">Paleontologists like me</a> know there are key moments in Earth’s history when extinction rates are high. For example, researchers have identified the <a href="https://doi.org/10.1038/nature09678">Big Five mass extinctions</a>: the five times over the past half billion years or so when more than three-quarters of the planet’s species have gone extinct in short order. Unfortunately, we are also now getting a good firsthand view of what extinction looks like, with the <a href="http://www.iucnredlist.org">rapid increase in extinction rates</a> over the last century.</p>
<p>But what factors make any one species more or less vulnerable to extinction? The <a href="https://www.elsevier.com/books/evolution-and-extinction-rate-controls/boucot/978-0-444-41182-2">rate of extinction varies</a> between different groups of animals and over time, so clearly not all species are equally susceptible. Scientists have done a great job of documenting extinction, but determining the processes that cause extinction has proved a bit more difficult. </p>
<h2>Who’s more vulnerable to extinction?</h2>
<p>Looking at modern examples, some tipping points that lead to the extinction of a species become obvious. <a href="https://doi.org/10.1098/rstb.2011.0015">Reduced population sizes is one such factor</a>. As the number of individuals of a species dwindles, it can lead to reduced genetic diversity and greater susceptibility to random catastrophic events. If the remaining population of a species is small enough, a single forest fire or even random variations in sex ratios <a href="https://www.scientificamerican.com/article/the-role-of-random-events/">could ultimately lead to extinction</a>. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/232787/original/file-20180820-30584-15rhcc8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/232787/original/file-20180820-30584-15rhcc8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/232787/original/file-20180820-30584-15rhcc8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/232787/original/file-20180820-30584-15rhcc8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/232787/original/file-20180820-30584-15rhcc8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/232787/original/file-20180820-30584-15rhcc8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/232787/original/file-20180820-30584-15rhcc8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/232787/original/file-20180820-30584-15rhcc8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1005&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">You won’t see another passenger pigeon.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/passenger-pigeon-wild-ectopistes-migratorius-188656403">Panaiotidi/Shutterstock.com</a></span>
</figcaption>
</figure>
<p>Extinctions that have occurred in the recent past receive a great deal of attention – for example, <a href="https://doi.org/10.1080/08912960802376199">the dodo</a>, <a href="https://theconversation.com/friday-essay-on-the-trail-of-the-london-thylacines-91473">thylacine</a> or <a href="https://news.nationalgeographic.com/news/2014/08/140831-passenger-pigeon-martha-deextinction-dna-animals-species/">passenger pigeon</a>. But the vast majority of extinctions happened well before the appearance of humans. The fossil record is thus the primary source of data on extinction.</p>
<p>When paleontologists consider fossils in the context of what we know about past environments, a clearer picture of what causes the extinction of species starts to emerge. To date, the likelihood of extinction of a species has been linked to a host of factors.</p>
<p>We certainly know that changes in temperature are one important element. Almost every major rise or fall in global temperatures in Earth history has resulted in the <a href="https://doi.org/10.1098/rspb.2007.1302">extinction of a swath of different organisms</a>.</p>
<p>The <a href="https://doi.org/10.1111/geb.12333">size of the geographic area a species occupies</a> is also crucial. Species that are broadly distributed are less likely to go extinct than those that occupy a small area or whose habitat is disjointed.</p>
<p>There are also random phenomena that cause extinction. The meteorite responsible for the extinction of about 75 percent of life at the end of the <a href="https://www.livescience.com/29231-cretaceous-period.html">Cretaceous Period</a>, including the non-avian dinosaurs, is perhaps the <a href="https://doi.org/10.1098/rstb.1994.0045">best example of this</a>. This random aspect to extinction is why some have argued that <a href="https://archive.nytimes.com/www.nytimes.com/books/97/11/09/home/gould-shale.html?_r=1">“survival of the luckiest” may be a better metaphor</a> for the history of life than “survival of the fittest.”</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/232779/original/file-20180820-30590-1ubepp8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/232779/original/file-20180820-30590-1ubepp8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/232779/original/file-20180820-30590-1ubepp8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=275&fit=crop&dpr=1 600w, https://images.theconversation.com/files/232779/original/file-20180820-30590-1ubepp8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=275&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/232779/original/file-20180820-30590-1ubepp8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=275&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/232779/original/file-20180820-30590-1ubepp8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=346&fit=crop&dpr=1 754w, https://images.theconversation.com/files/232779/original/file-20180820-30590-1ubepp8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=346&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/232779/original/file-20180820-30590-1ubepp8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=346&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Studying extinct mollusks’ fossils suggested physiological reasons one species might be more likely to disappear.</span>
<span class="attribution"><a class="source" href="http://neogeneatlas.net/species/anadara-aequalitas/">Hendricks, J. R., Stigall, A. L., and Lieberman, B. S. 2015. The Digital Atlas of Ancient Life: delivering information on paleontology and biogeography via the web. Palaeontologia Electronica, Article 18.2.3E</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">CC BY-NC-SA</a></span>
</figcaption>
</figure>
<p>Most recently, my colleagues and I identified a <a href="https://doi.org/10.1098/rspb.2018.1292">physiological component to extinction</a>. We found that the representative <a href="https://doi.org/10.1086/515881">metabolic rate</a> for both fossil and living mollusk species strongly predicts the likelihood of extinction. Metabolic rate is defined as the average rate of energy uptake and allocation by individuals of that species. Mollusk species with higher metabolic rates are more likely to go extinct than those with lower rates. </p>
<p>Returning to the metaphor of “survival of the fittest/luckiest,” this result suggests that “survival of the laziest” may apply at times. Higher metabolic rates correlate with higher mortality rates for individuals in both <a href="https://doi.org/10.1152/physrev.00047.2006">mammals</a> and <a href="https://doi.org/10.1186/1471-2148-6-67">fruit flies</a>, so metabolism may represent an important control on mortality at multiple biological levels. Because metabolic rate is linked to a constellation of characteristics including growth rate, time to maturity, maximum life span and maximum population size, it seems likely that the nature of any or all of these traits play a role in how vulnerable a species is to extinction. </p>
<h2>Plenty more extinction unknowns</h2>
<p>As much as scientists know about extinction drivers, there’s still a lot we don’t know. </p>
<p>For instance, some proportion of species go extinct regardless of any major environmental or biological upheaval. This is called the <a href="https://doi.org/10.1126/science.231.4734.129">background extinction rate</a>. Because paleontologists tend to focus on mass extinctions, background extinction rates are poorly defined. How much, or how little, this rate fluctuates isn’t well-understood. And, in total, most extinctions probably fall into this category.</p>
<p>Another problem is determining how important changing biological interactions are in explaining extinction. For instance, extinction of a species may occur when the abundance of a predator or a competitor increases, or when a crucial prey species goes extinct. The fossil record, however, rarely captures this kind of information. </p>
<p>Even the number of species that have gone extinct can be an enigma. We know very little about the current or past biodiversity of microorganisms, such as <a href="https://en.wikipedia.org/wiki/Bacteria">bacteria</a> or <a href="https://en.wikipedia.org/wiki/Archaea">archaea</a>, let alone anything about patterns of extinction for these groups.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/232782/original/file-20180820-30605-o7bf21.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/232782/original/file-20180820-30605-o7bf21.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/232782/original/file-20180820-30605-o7bf21.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=472&fit=crop&dpr=1 600w, https://images.theconversation.com/files/232782/original/file-20180820-30605-o7bf21.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=472&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/232782/original/file-20180820-30605-o7bf21.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=472&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/232782/original/file-20180820-30605-o7bf21.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=593&fit=crop&dpr=1 754w, https://images.theconversation.com/files/232782/original/file-20180820-30605-o7bf21.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=593&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/232782/original/file-20180820-30605-o7bf21.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=593&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Many animals – including the Scimitar-horned Oryx – are currently extinct in the wild.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/33590535@N06/3439149421">Drew Avery</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Perhaps the biggest mistake we could make when it comes to assessing and explaining extinction would be to take a one-size-fits-all approach. The vulnerability of any one species to extinction varies over time, and different biological groups respond differently to environmental change. While major changes in global climate have led to extinction in some biological groups, the same events have ultimately <a href="https://cup.columbia.edu/book/late-paleoceneearly-eocene-biotic-and-climatic-events-in-the-marine-and-terrestrial-records/9780231102384">led to the appearance of many new species</a> in others.</p>
<p>So how vulnerable any one species is to extinction due to human activities or the associated climate change remains sometimes an open question. It is clear that the current rate of extinction is rising well above anything that could be called background level, and is on track to be <a href="https://doi.org/10.1073/pnas.1704949114">the Sixth Mass Extinction</a>. The question of how vulnerable any one species – including our own – may be to extinction is therefore one scientists want to answer quickly, if we’re to have any chance of conserving future biodiversity.</p><img src="https://counter.theconversation.com/content/101773/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Luke Strotz is affiliated with the University of Kansas and his work is partly funded by the National Science Foundation.</span></em></p>Death is inevitable for individuals and also for species. With help from the fossil record, paleontologists are piecing together what might make one creature more vulnerable than another.Luke Strotz, Post-doctoral Researcher in Invertebrate Paleontology, University of KansasLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/912892018-02-07T00:03:20Z2018-02-07T00:03:20ZRainforest collapse in prehistoric times changed the course of evolution<p>Over <a href="https://rainforests.mongabay.com/amazon/deforestation_calculations.html">750,000 square kilometres</a> of Amazon rainforest have been cleared since 1970 – a fifth of the total. As a result, many of the animals that live there are <a href="https://www.theguardian.com/environment/2012/jul/12/amazon-deforestation-species-extinction-debt">threatened with extinction</a>. But this isn’t the first time the Earth has seen its rainforests shrink. Toward the end of the Carboniferous period, around 307m years ago, the planet’s environment shifted dramatically, and its vast tropical rainforests vanished.</p>
<p>Palaeontologists have previously struggled to work out how this rainforest collapse affected the first ancient vertebrate animals that lived there – the early tetrapods. This is because the fossil record for this time is patchy and incomplete. My colleagues and I have now <a href="http://rspb.royalsocietypublishing.org/lookup/doi/10.1098/rspb.2017.2730">published new research</a> that reveals how the collapse initially caused the number of species to fall, affecting water-loving amphibians the most. But this event ultimately paved the way for the ancestors of modern reptiles, mammals and birds – known as the amniotes – to flourish and spread across the globe.</p>
<p>About 310m years ago, long before the first dinosaurs and mammals evolved, North America and Europe lay in a single landmass at the equator covered by dense tropical rainforests, known as the “<a href="http://www.bbc.co.uk/nature/ancient_earth/Coal_forest">coal forests</a>”. The warm, humid climate and rich vegetation provided an <a href="https://theconversation.com/fossil-footprints-give-glimpse-of-how-ancient-climate-change-drove-the-rise-of-reptiles-69067">ideal habitat for amphibian-like early tetrapods</a>. This allowed them to quickly diversify into a variety of species.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/205041/original/file-20180206-14078-1e7te9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/205041/original/file-20180206-14078-1e7te9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=437&fit=crop&dpr=1 600w, https://images.theconversation.com/files/205041/original/file-20180206-14078-1e7te9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=437&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/205041/original/file-20180206-14078-1e7te9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=437&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/205041/original/file-20180206-14078-1e7te9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=549&fit=crop&dpr=1 754w, https://images.theconversation.com/files/205041/original/file-20180206-14078-1e7te9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=549&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/205041/original/file-20180206-14078-1e7te9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=549&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Carboniferous forest.</span>
<span class="attribution"><span class="source">Mark Ryan</span></span>
</figcaption>
</figure>
<p>Toward the end of the Carboniferous period, the number of tetrapod species had begun to increase greatly. But then the climate became much drier, causing a mass extinction of many species in the dominant plant groups, such as <a href="https://uwaterloo.ca/earth-sciences-museum/resources/calamite-fossils">horsetails</a> and <a href="https://www.uaex.edu/yard-garden/resource-library/plant-week/moss-giant-club-9-30-11.aspx">club mosses</a>.</p>
<p>Although the <a href="http://onlinelibrary.wiley.com/doi/10.1111/ter.12086/abstract">collapse of the rainforests</a> was a catastrophic event for plants, how it affected early tetrapods has remained largely uncertain. Previous analyses suggest that the number of <a href="http://www.bbc.co.uk/news/science-environment-11870322">early tetrapod species increased</a> through the collapse of the rainforests, but that the resulting fragmented landscape isolated different groups from each other, a pattern known as endemism.</p>
<h2>Fossil bias</h2>
<p>The problem with this research is that the early tetrapod fossil record is heavily biased. Much of what we know about early tetrapod evolution comes from extensively-studied fossil sites in midwestern and southern US, western Canada, and central Europe. This means our picture of early tetrapod evolution is biased around how much <a href="http://sp.lyellcollection.org/content/358/1/1.1">effort has been put into finding and identifying</a> fossils from these areas.</p>
<p>As with the dinosaurs, the reptile-like tetrapods of the Permian period, such as the sail-backed <a href="https://www.smithsonianmag.com/science-nature/the-dimetrodon-in-your-family-tree-54302176/"><em>Dimetrodon</em></a>, have captivated palaeontologists for many years. In contrast, the animals and landscapes of the Carboniferous period are relatively understudied. Palaeontologists and geologists are collaborating to <a href="https://www.nms.ac.uk/explore-our-collections/stories/natural-world/closing-romers-gap/">close these gaps in our knowledge</a>. Together, these biases limit our knowledge of early tetrapod diversity and can drastically affect analyses.</p>
<p>To address this problem, <a href="https://cordis.europa.eu/project/rcn/193499_en.html">my colleagues and I</a> turned to the <a href="https://paleobiodb.org/">Paleobiology Database</a>. This database is accessible to the public and is updated continuously by palaeobiologists with the location and age of all fossil finds from across the world. Instead of simply counting the species we have fossils for, we applied innovative statistical methods to the entire tetrapod fossil record.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/205049/original/file-20180206-14089-d02w8v.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/205049/original/file-20180206-14089-d02w8v.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=326&fit=crop&dpr=1 600w, https://images.theconversation.com/files/205049/original/file-20180206-14089-d02w8v.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=326&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/205049/original/file-20180206-14089-d02w8v.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=326&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/205049/original/file-20180206-14089-d02w8v.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=410&fit=crop&dpr=1 754w, https://images.theconversation.com/files/205049/original/file-20180206-14089-d02w8v.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=410&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/205049/original/file-20180206-14089-d02w8v.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=410&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Carboniferous fossil tetrapods in the Paleobiology Database.</span>
<span class="attribution"><span class="source">https://paleobiodb.org/navigator/</span></span>
</figcaption>
</figure>
<p>Our results, published in the Proceedings of the Royal Society B, reveal that tetrapod species diversity decreased after the rainforest collapse, with amphibians suffering the greatest losses. The drier climate would have reduced the amount of suitable habitats for amphibian species, which are dependent on wet environments and must return to water to spawn.</p>
<p>Instead of evidence for endemism, we found that tetrapod species that survived the rainforest collapse began to disperse more freely across the globe, colonising new habitats further from the equator. Many of these survivors were early amniotes, such as diadectids and <a href="http://www.bbc.co.uk/nature/life/Synapsid">synapsids</a>, animals that had considerable advantages over amphibians. They were generally larger so could travel longer distances, and because they laid eggs they were not confined to watery habitats.</p>
<p>While the fossil record of the Carboniferous and early Permian Periods is strongly biased, new statistical methods that address these biases have allowed us to examine the true impact of the rainforest collapse on early tetrapods. We now know that the event was crucial in paving the way for amniotes, the group that ultimately gave rise to the dinosaurs and eventually modern reptiles, mammals and birds, to become the dominant group of land vertebrates.</p><img src="https://counter.theconversation.com/content/91289/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Emma Dunne receives funding from the European Research Council through its Horizon 2020 programme. </span></em></p>A drying climate caused a mass extinction among plants, but paved the way for the ancestors of modern reptiles, mammals, and birds.Emma Dunne, PhD student, University of BirminghamLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/799712017-06-29T09:37:22Z2017-06-29T09:37:22ZFive mass extinctions – and what we can learn from them about the planet today<figure><img src="https://images.theconversation.com/files/175881/original/file-20170627-24767-xswmix.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/lava-lake-flow-night-nyiragongo-dr-576621556">Kiki Dohmeier/Shutterstock</a></span></figcaption></figure><p>Of all the species that have ever lived, <a href="https://books.google.co.uk/books?id=4LHnCAAAQBAJ&pg=PA110&lpg=PA110&dq=&redir_esc=y#v=onepage&q&f=false">more than 99% are now extinct</a>. Most of them quietly disappeared during periods of “background extinction”, whereby a handful of species become extinct every 100,000 years or so. </p>
<p>But there were also occasions when extinction rates increased rapidly in short periods of time and wiped out a significant proportion of all life on Earth. These are known as mass extinctions. They have profoundly influenced the history of life – and many scientists now argue that we are <a href="https://theconversation.com/earths-sixth-mass-extinction-has-begun-new-study-confirms-43432">in the midst of another one</a>. To see if they’re right, we can look at previous occasions when large numbers of species went extinct. </p>
<p>Traditionally, scientists have referred to the “Big Five” mass extinctions, including perhaps the most famous mass extinction that brought about the <a href="https://theconversation.com/did-a-burning-oil-spill-wipe-out-the-dinosaurs-62456?sr=8">end of the dinosaurs</a>. This was triggered by a meteorite impact at the end of the Cretaceous period, but the other major mass extinctions were caused by phenomena originating entirely on Earth. While they are less well known, we may learn something from exploring them that could shed light on our current environmental crises. </p>
<h2>1. The Late Ordovician</h2>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/176025/original/file-20170628-7294-b72keo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/176025/original/file-20170628-7294-b72keo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/176025/original/file-20170628-7294-b72keo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/176025/original/file-20170628-7294-b72keo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/176025/original/file-20170628-7294-b72keo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/176025/original/file-20170628-7294-b72keo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/176025/original/file-20170628-7294-b72keo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Global cooling has led to mass extinction.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/funkadelic/20057917/">Mark Brennan/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>This ancient crisis around 445m years ago saw two major waves of extinction, both caused by climate change associated with the advance and retreat of <a href="http://annualreviews.org/doi/abs/10.1146/annurev.earth.29.1.331">ice sheets in the southern hemisphere</a>. This makes it the only major extinction to be linked to global cooling. </p>
<p>This extinction caused the demise of around 57% of marine genera (<a href="https://www.sciencelearn.org.nz/resources/1438-classification-system">the taxonomic rank</a> above the species level), including many <a href="http://www.bbc.co.uk/nature/life/Trilobite">trilobites</a>, shelled <a href="http://www.bgs.ac.uk/discoveringGeology/time/fossilfocus/brachiopod.html">brachiopods</a>, and eel-like <a href="http://www.le.ac.uk/gl/map2/abstractsetc/RWwww.html">conodonts</a>.</p>
<h2>2. The Late Devonian</h2>
<p>This period is now regarded as a number of “pulses” of extinction <a href="http://www.bbc.co.uk/nature/extinction_events/Late_Devonian_extinction">spread over 20m years</a>, beginning 380m years ago. It saw the extinction of around 50% of marine genera; among the species killed off were many corals, trilobites, sponges and the <a href="http://www.pnas.org/content/107/22/10131.short">heavily armoured fish known as placoderms</a>. This extinction has been linked to major climate change, possibly caused by an eruption of the volcanic <a href="http://www.sciencedirect.com/science/article/pii/S0012821X10006321">Viluy Traps</a> area in modern-day Siberia. A major eruption might have caused <a href="http://www.sciencedirect.com/science/article/pii/S0031018208001697">rapid fluctations in sea levels</a> and reduced oxygen levels in the oceans.</p>
<h2>3. The Middle Permian</h2>
<p>Scientists have recently <a href="http://www.sciencedirect.com/science/article/pii/S0031018212007018">discovered another event 262m years ago</a> that rivals the “Big Five” in size. This event coincided with the <a href="http://www.sciencedirect.com/science/article/pii/S1674987113001072">Emeishan eruption</a> in what’s now China, and is known to have caused <a href="http://gsabulletin.gsapubs.org/content/127/9-10/1411.short">simultaneous extinctions in the tropics and higher latitudes</a>. In particular, there were exceptionally high extinction rates: <a href="http://gsabulletin.gsapubs.org/content/127/9-10/1411.short">more than 80%</a> of species were wiped out, among them brachiopods and single-celled <a href="http://www.sepmstrata.org/page.aspx?pageid=721">benthic foraminifera</a>.</p>
<h2>4. The Late Permian</h2>
<p>The Late Permian mass extinction around 252m years ago dwarfs all the other events, with <a href="http://www.sciencedirect.com/science/article/pii/S0169534703000934">about 96% of species becoming extinct</a>. This included more trilobites, corals, and whole branches of species of terrestrial animals. The extinction was triggered by a vast eruption of the <a href="http://news.mit.edu/2015/siberian-traps-end-permian-extinction-0916">Siberian Traps</a>, a gigantic and prolonged volcanic event that covered much of modern day Siberia, which led to a cascade of environmental effects. </p>
<p>A greenhouse effect rapidly took hold in the atmosphere, while the oceans suffered acidification and oxygen depletion. The ozone layer was partially destroyed, meaning lethal levels of UV radiation reached the Earth’s surface. The recovery took <a href="http://www.nature.com/ngeo/journal/v5/n6/abs/ngeo1475.html">almost 10m years</a> and even then, the <a href="http://science.sciencemag.org/content/338/6105/366">unstable environment</a> this catastrophic crisis created meant the subsequent Triassic period saw intermittent bursts of heightened extinction.</p>
<h2>5. The Late Triassic</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/175622/original/file-20170626-321-1nv0jzr.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/175622/original/file-20170626-321-1nv0jzr.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/175622/original/file-20170626-321-1nv0jzr.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=675&fit=crop&dpr=1 600w, https://images.theconversation.com/files/175622/original/file-20170626-321-1nv0jzr.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=675&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/175622/original/file-20170626-321-1nv0jzr.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=675&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/175622/original/file-20170626-321-1nv0jzr.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=848&fit=crop&dpr=1 754w, https://images.theconversation.com/files/175622/original/file-20170626-321-1nv0jzr.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=848&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/175622/original/file-20170626-321-1nv0jzr.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=848&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The supercontinent Pangaea before it split.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/w/index.php?curid=48962">Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The Late Triassic event, 201m years ago, shares a number of similarities with the Late Permian event. It was caused by another large-scale eruption, this time of the <a href="http://science.sciencemag.org/content/340/6135/941">Central Atlantic Magmatic Province</a>, which heralded the splitting of the supercontinent <a href="http://www.bbc.co.uk/science/earth/earth_timeline/pangaea">Pangaea</a> and the initial opening of what would later become the Atlantic Ocean.</p>
<p>A similar <a href="http://specialpapers.gsapubs.org/content/early/2014/06/10/2014.2505_02.abstract">cascade of environmental effects</a>, as seen during the Late Permian, led to the extinction of around 47% of all genera. The extinction led to the final demise of the eel-like <a href="http://www.le.ac.uk/gl/map2/abstractsetc/RWwww.html">conodonts</a>, as well as the largest known extinction of <a href="http://www.ucmp.berkeley.edu/cnidaria/scleractinia.html">scleractinian corals</a>. It also wiped out a significant proportion of <a href="https://www.nature.com/articles/ncomms8980">terrestrial reptiles and amphibians</a>, <a href="https://theconversation.com/new-evidence-that-volcanic-eruptions-triggered-the-dawn-of-the-dinosaurs-79729?sr=2">paving the way</a> for the diversification of the dinosaurs in the Jurassic period.</p>
<h2>A mass extinction in slow motion</h2>
<p>So, are we currently in the middle of a mass extinction? If we really are, this time the cause is not a meteorite impact or volcanic eruptions. It is the work of a single species: <em>Homo sapiens</em>. Habitat destruction and climate change from rising carbon dioxide levels has driven extinction rates to levels <a href="http://www.nature.com/nature/journal/v471/n7336/abs/nature09678.html">reminiscent of the mass extinctions of the ancient past</a>.</p>
<p>The similarities between today and the past are uncanny. The majority of past extinctions are associated with carbon dioxide from volcanoes causing rapid global warming, which led to a number of environmental cascade effects. The cause may be different, but the results will be the same.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/175585/original/file-20170626-32751-19kn5ya.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/175585/original/file-20170626-32751-19kn5ya.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/175585/original/file-20170626-32751-19kn5ya.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/175585/original/file-20170626-32751-19kn5ya.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/175585/original/file-20170626-32751-19kn5ya.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/175585/original/file-20170626-32751-19kn5ya.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/175585/original/file-20170626-32751-19kn5ya.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/175585/original/file-20170626-32751-19kn5ya.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Habitat destruction fuelling the current crisis.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/tree-stumps-after-deforestation-located-around-284015750?src=54_4VUrdzy7umBpviHSAnA-1-5">Nina Lishchuk/Shutterstock</a></span>
</figcaption>
</figure>
<p>However, it is now 66m years since the last mass extinction. Earth’s ecosystems are very different, and perhaps more stable given the length of time elapsed since the last major biotic crisis. The position of the continents has changed, meaning atmospheric and ocean circulation are different; that makes it very difficult to use past data to predict the outcomes of any future mass extinctions.</p>
<p>Current extinction rates are <a href="http://advances.sciencemag.org/content/1/5/e1400253.short">50 times higher than expected background rates</a>, suggesting that another mass extinction event is underway. But mass extinctions are also about magnitude: if we could travel millions of years into the future and examine rocks preserving today’s ecosystems, I’d wager we’d see little evidence of a major extinction event.</p>
<p>If we can stop the biodiversity decline in the near future, we may yet escape mass extinction. But 100 or 1,000 years more of human-caused stress on the biosphere will likely tip us over the edge into oblivion.</p><img src="https://counter.theconversation.com/content/79971/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Alex Dunhill receives funding from the Leverhulme Trust and the Natural Environment Research Council.</span></em></p>Are we in the middle of a mass extinction caused by Homo sapiens? Past events can help us to understand the current crisis.Alex Dunhill, Research Fellow in Palaeobiology, University of LeedsLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/789372017-06-22T10:08:29Z2017-06-22T10:08:29ZCould asteroids bombard the Earth to cause a mass extinction in ten million years?<figure><img src="https://images.theconversation.com/files/174539/original/file-20170619-28475-1ispdog.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Elenarts/Shutterstock</span></span></figcaption></figure><p>Scientists <a href="https://www.nature.com/nature/journal/v308/n5961/abs/308718a0.html">have spent decades debating</a> whether asteroids and comets hit the Earth at regular intervals. At the same time, a few studies <a href="https://www.ncbi.nlm.nih.gov/pubmed/17788674">have found evidence</a> that the large extinction events on Earth – such as the one that wiped out the dinosaurs 66m years ago – repeat themselves every 26m to 30m years. Given that there’s good evidence that an asteroid triggered the dinosaur extinction, it makes sense to ask whether showers of asteroids could be to blame for regular extinction events. </p>
<p>The question is extremely important – if we could prove that this is the case, then we might be able to predict and even prevent asteroids causing mass extinctions in the future. We have tried to find out the answer.</p>
<p>Today, there are approximately 190 impact craters from asteroids and comets on Earth. They range in size from only a few meters to more than 100km across. And they formed anywhere between a few years ago and more than two billion years ago. Only a few, like the famous <a href="http://www.nytimes.com/2009/01/23/travel/escapes/23Flagstaff.html">“Meteor crater” in Arizona</a>, are visible to the untrained eye, but scientists have learned to recognise impact craters even if they are covered by lakes, the ocean or thick layers of sediment.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/175065/original/file-20170621-30227-1tkxt1g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/175065/original/file-20170621-30227-1tkxt1g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/175065/original/file-20170621-30227-1tkxt1g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/175065/original/file-20170621-30227-1tkxt1g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/175065/original/file-20170621-30227-1tkxt1g.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/175065/original/file-20170621-30227-1tkxt1g.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/175065/original/file-20170621-30227-1tkxt1g.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Meteor crater, Arizona.</span>
<span class="attribution"><span class="source">Kevin Walsh/wikipedia</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>But have these craters formed as a result of regular asteroid collisions? And if so, why? There have been many suggestions, but most prominently, some scientists have suggested that the <a href="https://theconversation.com/did-dark-matter-or-a-star-called-nemesis-kill-the-dinosaurs-51846?sr=1">sun has a companion star</a> (called “Nemesis”) on a very wide orbit, which approaches the solar system every 26m to 30m years and thereby triggers showers of comets. </p>
<p>Nemesis would be a red/brown dwarf star – a faint type of star – orbiting the sun at a distance of about 1.5 light years. This is not an impossible idea, since the majority of stars <a href="http://news.berkeley.edu/2017/06/13/new-evidence-that-all-stars-are-born-in-pairs/">actually belong to systems with more than one star</a>. However, despite searching for it for decades, astronomers have failed to observe it, and think they can now exclude its existence.</p>
<h2>Difficult dating</h2>
<p>Yet, the idea of periodic impacts persists. There are other suggestions. One idea is based on the observation that the sun moves up and down slightly as it orbits the galaxy, crossing the galactic disk every 30m years or so. Some have suggested that this could somehow trigger comet showers. </p>
<p>But is there any evidence that asteroid impacts occur at regular intervals? Most research so far has failed to show this. But that doesn’t mean it isn’t the case – it’s tricky getting the statistics right. There are a lot of variables involved: craters disappear as they age, and some are never found in the first place as they are on the ocean floor. Rocks from some periods are easier to find than from others. And determining the ages of the craters is difficult. </p>
<p>A recent study <a href="https://academic.oup.com/mnras/article-abstract/454/4/3480/992970/Periodic-impact-cratering-and-extinction-events?redirectedFrom=fulltext">claimed to have found evidence</a> of periodicity. However, the crater age data it used included many craters with poorly known, or even incorrect and outdated ages. The methods used to determine age – based on radioactive decay or looking at microscopic fossils with known ages – are continuously improved by scientists. Therefore, today, the age of an impact event can be improved significantly from an initial analysis made, say, ten or 20 years ago. </p>
<p>Another problem involves impacts that have near identical ages with exactly the same uncertainty in age: known as “clustered ages”. The age of an impact crater may be, for example, 65.5 ± 0.5m years while another is be 66.1 ± 0.5m years. In this case, both craters might have the same true age of 65.8m years. Such craters have in some instances been produced by impacts of asteroids accompanied by small moons, or by asteroids that broke up in the Earth’s atmosphere. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/175066/original/file-20170621-25561-1k5v7f6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/175066/original/file-20170621-25561-1k5v7f6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=398&fit=crop&dpr=1 600w, https://images.theconversation.com/files/175066/original/file-20170621-25561-1k5v7f6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=398&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/175066/original/file-20170621-25561-1k5v7f6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=398&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/175066/original/file-20170621-25561-1k5v7f6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=500&fit=crop&dpr=1 754w, https://images.theconversation.com/files/175066/original/file-20170621-25561-1k5v7f6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=500&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/175066/original/file-20170621-25561-1k5v7f6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=500&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Manicouagan crater in Canada seen from the International Space Station/</span>
<span class="attribution"><span class="source">NASA/Chris Hadfield</span></span>
</figcaption>
</figure>
<p>The double impact craters they produce can make it look like they hit a time when there were lots of asteroid impacts, when actually the craters were formed in the same event. In some cases, clustered impact craters are spaced too far apart to be explained as double impacts. So how could we explain them? The occasional collision of asteroids in the asteroid belt between Mars and Jupiter might trigger short-lived “showers” of asteroids impacting the Earth. Only a few of these showers are necessary to lead to the false impression of periodicity.</p>
<h2>Fresh approach</h2>
<p>In contrast to previous studies, we restricted our statistical analysis to 22 impact craters with very well defined ages from the past 260m years. In fact, these all have age uncertainties of less than 0.8%. We also accounted for impacts with clustered ages. </p>
<p>Our article, <a href="https://academic.oup.com/mnras/article-lookup/doi/10.1093/mnras/stx211">recently published in Monthly Notices of the Royal Astronomical Society</a>, shows that, to the best of our current knowledge, asteroid impacts do not happen at regular intervals – they seem to occur randomly. </p>
<p>Of course, we can’t be sure that there isn’t any periodicity. But the good news is that, as more impact craters are dated with robust ages, the statistical analysis we did can be repeated over and over again – if there is such a pattern, it should become visible at some point.</p>
<p>That means that there is presently no way to predict when a large asteroid collision may once again threaten life on Earth. But then when it comes to facing the apocalypse, maybe not knowing is not so bad after all …</p><img src="https://counter.theconversation.com/content/78937/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Matthias Meier receives funding from the Swiss National Science Foundation.</span></em></p><p class="fine-print"><em><span>Sanna Alwmark does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Researchers are looking at whether devastating asteroid strikes are predictable or random.Sanna Alwmark, Doctoral Candidate of Lithosphere and Biosphere Science, Lund UniversityMatthias Meier, Swiss National Science Foundation Ambzione Fellow in Geo- and Cosmochemistry, Swiss Federal Institute of Technology ZurichLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/782292017-06-21T10:31:12Z2017-06-21T10:31:12ZReverse engineering mysterious 500-million-year-old fossils that confound our tree of life<figure><img src="https://images.theconversation.com/files/174773/original/file-20170620-5990-1lz2lmr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Here's the fossil... what can you tell about how this animal lived?</span> <span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Parvancorina_minchami_-_MUSE.jpg">Matteo De Stefano/MUSE-Science Museum</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Paleontologists like us are used to working with fossils that would seem bizarre to many biologists accustomed to living creatures. And as we go farther back in Earth’s history, the fossils start to look even weirder. They lack tails, legs, skeletons, eyes…any characteristics that would help us understand where these organisms fit in the tree of life. Under these circumstances, the science of paleontology becomes significantly harder.</p>
<p>Nowhere is this issue more apparent than in <a href="https://doi.org/10.1080/00241160500409223">the Ediacaran period</a>, which lasted from 635 million to 541 million years ago. A peculiar and entirely soft-bodied suite of fossils from this era are collectively referred to <a href="https://doi.org/10.1146/annurev.earth.33.092203.122519">as the Ediacara biota</a>. Despite <a href="http://www.biodiversitylibrary.org/page/41347851#page/235/mode/1up">nearly 70 years of careful study</a>, paleontologists have yet to identify key features among them that would allow us to understand how these organisms are related to modern animals. The forms evident among Ediacaran organisms are, for the most part, truly unique – and we are no closer to understanding their place in evolutionary history.</p>
<p>Rather than looking for characteristics that would allow us to shoehorn some of these organisms into known animal groups, <a href="https://doi.org/10.1098/rsbl.2017.0033">we’ve taken a different approach</a>. It relies on a technique called computational fluid dynamics that lets us reverse engineer how these organisms lived in their ocean environment.</p>
<h2>Mystery fossils</h2>
<p>The Ediacaran period marks a pivotal interval in Earth’s history; at its start are the last of the so-called “<a href="https://theconversation.com/us/topics/snowball-earth-16060">Snowball Earth</a>” events – episodes lasting millions of years when the entire surface of our planet was covered in ice. It segues into the succeeding Cambrian geological period, which saw the first appearance of many of the animal groups we recognize in the present day. This is what’s commonly referred to as the <a href="https://theconversation.com/uk/topics/cambrian-explosion-7159">Cambrian explosion</a>.</p>
<p>When large, complex fossils were discovered in the Ediacaran, researchers naturally expected that many of them would represent early relatives of the same animal groups that had been recognized in the Cambrian. But these Ediacarans seem completely distinct from modern animals.</p>
<p>For instance, <a href="https://doi.org/10.1126/science.1099727">the rangeomorphs</a> were a collection of leaf- and mat-like organisms with a unique fractal architecture, constructed from a series of branching “frond” elements, each a few centimeters long, each of which is itself composed of smaller, identical frond elements.</p>
<p>Another – <em>Tribrachidium</em> – was a small hemispherical organism possessing three raised branches that meet at the top of the organism and which curved toward the margin in a counterclockwise direction.</p>
<p>So how do oddballs like these fit in with what came before and what came after? We just haven’t been able to place them on any evolutionary tree.</p>
<p>In order to better understand these organisms, paleontologists have been forced to adopt a different approach. We’ve abandoned all assumptions about what they might be related to, and instead tried to answer more fundamental questions. For instance, did they move? How did they feed? How did they reproduce? By answering these questions, we can begin to understand their biology and ecology, which in turn may provide hints as to how these organisms are related to other multicellular lifeforms. This is how we’ve begun to reverse engineer the Ediacara biota. </p>
<h2>Modeling fluid dynamics to reverse engineer fossils</h2>
<p>One of the most important techniques at our disposal is computational fluid dynamics (CFD), a method for virtually simulating fluid flows around objects using computers.</p>
<p>The rationale for using this approach lies in observing organisms in modern oceans. We know that many (if not all) animals living in shallow marine environments have evolved adaptations that allow them to interact with and manipulate currents, either to reduce drag and prevent them from being swept away (think limpets and barnacles), or to aid in feeding (think crinoids, sea anemones and gorgonian corals). So we can learn a lot about an organism’s biology and ecology by studying the way it behaves in moving fluids.</p>
<p>With modern species, researchers can study fluid flows around living animals. But for organisms that have been extinct for over half a billion years – such as the Ediacara biota – virtual simulations using CFD are the only approach.</p>
<p>Here’s how we do it. First, we obtain a digital 3-D model of a fossil and place it in a virtual flume tank. Then, we simulate water flowing over and around the digital fossil. Visualizing patterns of flow and recirculation around the organism allows us to test hypotheses about how the organism moved and fed. With something as mysterious and obscure as the Ediacara biota, these insights may bring us closer to understanding what they are.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/174776/original/file-20170620-32348-25ho6r.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/174776/original/file-20170620-32348-25ho6r.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/174776/original/file-20170620-32348-25ho6r.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=251&fit=crop&dpr=1 600w, https://images.theconversation.com/files/174776/original/file-20170620-32348-25ho6r.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=251&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/174776/original/file-20170620-32348-25ho6r.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=251&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/174776/original/file-20170620-32348-25ho6r.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=315&fit=crop&dpr=1 754w, https://images.theconversation.com/files/174776/original/file-20170620-32348-25ho6r.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=315&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/174776/original/file-20170620-32348-25ho6r.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=315&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Schematic reconstructions of various <em>Parvancorina</em> species.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Parvancorina_species.png">Aleksey Nagovitsyn</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Our recent work with the enigmatic Ediacaran fossil <em>Parvancorina</em> is an example of this approach. <em>Parvancorina</em> is a simple-looking, shield-shaped organism typically 1-2 centimeters in length, with an anchor-like series of ridges on its top surface. Although it’s been interpreted in a variety of ways, most scientists have assumed that it was fixed on the seafloor – what we call sessile. No one has seen any limbs preserved with <em>Parvancorina</em> and it’s never been found in association with fossilized tracks or trails.</p>
<p>We decided to test this idea by building 3-D models of the two known <em>Parvancorina</em> species, and then using CFD to see how their unique surface structures affected patterns of fluid flow in different orientations. Our results showed that patterns of water flow around the model were dramatically different depending on the how it was oriented in the current.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/174769/original/file-20170620-32365-1mgzxxh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/174769/original/file-20170620-32365-1mgzxxh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/174769/original/file-20170620-32365-1mgzxxh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=380&fit=crop&dpr=1 600w, https://images.theconversation.com/files/174769/original/file-20170620-32365-1mgzxxh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=380&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/174769/original/file-20170620-32365-1mgzxxh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=380&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/174769/original/file-20170620-32365-1mgzxxh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=478&fit=crop&dpr=1 754w, https://images.theconversation.com/files/174769/original/file-20170620-32365-1mgzxxh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=478&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/174769/original/file-20170620-32365-1mgzxxh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=478&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Digital models of <em>Parvancorina</em>. Center and right columns: results of CFD analyses showing fluid flow around <em>Parvancorina</em> in different orientations. Flow direction is indicated by arrows, and velocity indicated by colors (in meters per second), with faster flow in red colors, and slow flow in blue colors.</span>
<span class="attribution"><span class="source">Darroch and Rahman</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Assuming <em>Parvancorina</em> was a suspension feeder, our results demonstrate that it would have been good at capturing the food in the ocean water only when it was oriented in a single specific direction. This is obviously bad news if you’re a sessile suspension feeder, <a href="https://doi.org/10.1126/sciadv.1500800">like some other members of the Ediacara biota</a>. If you rely on the current to carry water laden with nutrients and food particles to your mouth or feeding apparatus, you want that to happen no matter which way the current is flowing. If you’re stuck in one place and the current changes, you’ve got a problem if you can only gather food when it’s coming at you from one direction. Any other plausible style of feeding – for example, scavenging – would also imply these creatures had a mobile lifestyle.</p>
<p>We also used these simulations to calculate drag in different orientations. Although talking about front and back ends in <em>Parvancorina</em> is slightly problematic (because we can’t even tell whether it had anything resembling a head and tail), we usually think of the shield end as the front. We showed that the drag experienced by <em>Parvancorina</em> was typically lower when it was placed front-on to current, compared to when it was placed side-on. This is also bad news if you’re a sessile organism, because it leaves you open to being ripped from the sediment in strong currents.</p>
<p>The inference from these two observations is clear: <em>Parvancorina</em> was <a href="https://doi.org/10.1098/rsbl.2017.0033">better adapted to life as a mobile, rather than a sessile, organism</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/174779/original/file-20170620-32333-142po1q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/174779/original/file-20170620-32333-142po1q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/174779/original/file-20170620-32333-142po1q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/174779/original/file-20170620-32333-142po1q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/174779/original/file-20170620-32333-142po1q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/174779/original/file-20170620-32333-142po1q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/174779/original/file-20170620-32333-142po1q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/174779/original/file-20170620-32333-142po1q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">No one knows what life was like in the seas of the Ediacaran period, but research like this can start to fill in some details.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/ideonexus/2237406519">Ryan Somma</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>New understanding of <em>Parvancorina</em> lifestyle</h2>
<p>This conclusion may sound like a minor footnote in the story of life on Earth. But we believe it has powerful implications for how we view the Ediacara biota as a whole.</p>
<p>First, so little is currently known about <em>Parvancorina</em> that any additional information is crucial. The knowledge that it was mobile will help us work out where this fossil fits in the tree of life.</p>
<p>Second, the inference that <em>Parvancorina</em> was mobile, but nonetheless left no trace of its movement, is important – it means that many other Ediacaran fossils that we’ve assumed were sessile may actually have been mobile as well. This may require us to reimagine Ediacaran ecosystems as much more dynamic and, by extension, much more complex than we previously thought.</p>
<p>Through using tools like computational fluid dynamics to reverse engineer the Ediacara biota, we’re getting closer to understanding what they represent, and how they lived and functioned 15 million years before the Cambrian explosion.</p><img src="https://counter.theconversation.com/content/78229/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Simon Darroch receives funding from the Paleontological Society and National Geographic. </span></em></p><p class="fine-print"><em><span>Imran Rahman receives funding from the Oxford University Museum of Natural History. </span></em></p>With no identifiable body parts, it’s hard to know how these fossilized creatures lived. A new approach models how the ocean’s water would interact with their unique shapes – hinting at their lifestyle.Simon Darroch, Assistant Professor of Earth and Environmental Sciences, Vanderbilt UniversityImran Rahman, Junior Research Fellow, University of OxfordLicensed as Creative Commons – attribution, no derivatives.