tag:theconversation.com,2011:/au/topics/tetrapods-8680/articlesTetrapods – The Conversation2024-02-06T21:38:09Ztag:theconversation.com,2011:article/2193972024-02-06T21:38:09Z2024-02-06T21:38:09ZA 380-million-year old predatory fish from Central Australia is finally named after decades of digging<figure><img src="https://images.theconversation.com/files/568893/original/file-20240111-21-jl663h.jpg?ixlib=rb-1.1.0&rect=609%2C0%2C2039%2C1138&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Harajicadectes cruises through the ancient rivers of central Australia ~385 million years ago.</span> <span class="attribution"><span class="source">Brian Choo</span></span></figcaption></figure><p>More than 380 million years ago, a sleek, air-breathing predatory fish patrolled the rivers of central Australia. Today, the sediments of those rivers are outcrops of red sandstone in the remote outback.</p>
<p>Our new paper, published in the <a href="https://www.tandfonline.com/doi/full/10.1080/02724634.2023.2285000">Journal of Vertebrate Paleontology</a>,
describes the fossils of this fish, which we have named <em>Harajicadectes zhumini</em>. </p>
<p>Known from at least 17 fossil specimens, <em>Harajicadectes</em> is the first reasonably complete bony fish found from Devonian rocks in central Australia. It has also proven to be a most unusual animal.</p>
<h2>Meet the biter</h2>
<p>The name means “Min Zhu’s Harajica-biter”, after the location where its fossils were found, its presumed predatory habits, and in honour of eminent Chinese palaeontologist <a href="http://english.ivpp.cas.cn/people/members/202305/t20230530_331150.html">Min Zhu</a>, who has made many contributions to <a href="https://theconversation.com/a-kung-fu-kick-led-researchers-to-the-worlds-oldest-complete-fish-fossils-heres-what-they-found-190749">early vertebrate research</a>. </p>
<p><em>Harajicadectes</em> was a fish in the <a href="https://en.wikipedia.org/wiki/Tetrapodomorpha">Tetrapodomorpha</a> group. This group had strongly built paired fins and usually only a single pair of external nostrils.</p>
<p>Tetrapodomorph fish from the Devonian period (359–419 million years ago) have long been of great interest to science. They include the forerunners of modern tetrapods – animals with backbones and limbs such as amphibians, reptiles, birds and mammals.</p>
<p>For example, recent fossil discoveries show fingers and toes arose <a href="https://www.nature.com/articles/s41586-020-2100-8">in this group</a>. </p>
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Read more:
<a href="https://theconversation.com/when-fish-gave-us-the-finger-this-ancient-four-limbed-fish-reveals-the-origins-of-the-human-hand-129072">When fish gave us the finger: this ancient four-limbed fish reveals the origins of the human hand</a>
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<p>Devonian fossil sites in <a href="https://www.youtube.com/watch?v=LnHVPgvrn2M">northwestern</a> and <a href="https://australian.museum/learn/australia-over-time/fossils/sites/canowindra/">eastern</a> Australia have produced many spectacular discoveries of early tetrapodomorphs.</p>
<p>But until our discovery, the poorly sampled interior of the continent had only offered tantalising fossil fragments. </p>
<h2>A long road to discovery</h2>
<p>Our species description is the culmination of 50 years of tireless exploration and research. </p>
<p>Palaeontologist Gavin Young from the Australian National University made the initial discoveries in 1973 while exploring the Middle-Late Devonian Harajica Sandstone on Luritja/Arrernte country, more than 150 kilometres west of Alice Springs (Mparntwe).</p>
<p>Packed within red sandstone blocks on a remote hilltop were hundreds of fossil fishes. The vast majority of them were small <em>Bothriolepis</em> – a type of widespread prehistoric fish known as a <a href="https://en.wikipedia.org/wiki/Placodermi">placoderm</a>, covered in box-like armour.</p>
<p>Scattered among them were fragments of other fishes. These included <a href="https://bioone.org/journals/Acta-Palaeontologica-Polonica/volume-54/issue-4/app.2008.0057/A-New-Genus-of-Lungfish-from-the-Givetian-Middle-Devonian/10.4202/app.2008.0057.full">a lungfish known as <em>Harajicadipterus youngi</em></a>, named in honour of Gavin Young and his years of work on material from Harajica.</p>
<p>There were also spines from acanthodians (small, vaguely shark-like fish), the plates of phyllolepids (extremely flat placoderms) and, most intriguingly, jaw fragments of a previously unknown tetrapodomorph. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/565947/original/file-20231215-21-3lshgi.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/565947/original/file-20231215-21-3lshgi.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/565947/original/file-20231215-21-3lshgi.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/565947/original/file-20231215-21-3lshgi.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/565947/original/file-20231215-21-3lshgi.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/565947/original/file-20231215-21-3lshgi.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/565947/original/file-20231215-21-3lshgi.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/565947/original/file-20231215-21-3lshgi.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">The moment of discovery when we found a complete fossil of <em>Harajicadectes</em> in 2016. Flinders University palaeontologists John Long (centre), Brian Choo (right) and Alice Clement (left) with ANU palaeontologist Gavin Young (top left).</span>
<span class="attribution"><span class="source">Author provided</span></span>
</figcaption>
</figure>
<p>Many more partial specimens of this Harajica tetrapodomorph were collected in 1991, including some by the late palaeontologist <a href="https://www.smh.com.au/national/the-man-who-found-4000-fish-fossils-in-a-nsw-country-town-20231205-p5ep2m.html">Alex Ritchie</a>.</p>
<p>There were early attempts at figuring out the species, but this proved troublesome. Then, our Flinders University expedition to the site in 2016 yielded the first almost complete fossil of this animal.</p>
<p>This beautiful specimen demonstrated that all the isolated bits and pieces collected over the years belonged to a single new type of fish. It is now in the collections of the Museum and Art Gallery of the Northern Territory, serving as the <a href="https://museum.wa.gov.au/explore/blogs/museumcollections/what-type-specimen">type specimen</a> of <em>Harajicadectes</em>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/567575/original/file-20240102-21-i0b5nl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A sandstone image of a fish shape along with two graphics showing it in more detail" src="https://images.theconversation.com/files/567575/original/file-20240102-21-i0b5nl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/567575/original/file-20240102-21-i0b5nl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=448&fit=crop&dpr=1 600w, https://images.theconversation.com/files/567575/original/file-20240102-21-i0b5nl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=448&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/567575/original/file-20240102-21-i0b5nl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=448&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/567575/original/file-20240102-21-i0b5nl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=563&fit=crop&dpr=1 754w, https://images.theconversation.com/files/567575/original/file-20240102-21-i0b5nl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=563&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/567575/original/file-20240102-21-i0b5nl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=563&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 type specimen of <em>Harajicadectes</em> discovered in 2016.</span>
<span class="attribution"><span class="source">Author provided</span></span>
</figcaption>
</figure>
<h2>A strange apex predator</h2>
<p>Up to 40 centimetres long, <em>Harajicadectes</em> is the biggest fish found in the Harajica rocks. Likely the top predator of those ancient rivers, its big mouth was lined with closely-packed sharp teeth alongside larger, widely spaced triangular fangs.</p>
<p>It seems to have combined anatomical traits from different tetrapodomorph lineages via convergent evolution (when different creatures evolve similar features independently). An example of this are the patterns of bones in its skull and scales. Exactly where it sits among its closest relatives is difficult to resolve. </p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/569190/original/file-20240114-27-x8x87i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A large fish seen on the bottom of the sea with two smaller armoured fish underneath it" src="https://images.theconversation.com/files/569190/original/file-20240114-27-x8x87i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/569190/original/file-20240114-27-x8x87i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=781&fit=crop&dpr=1 600w, https://images.theconversation.com/files/569190/original/file-20240114-27-x8x87i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=781&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/569190/original/file-20240114-27-x8x87i.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=781&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/569190/original/file-20240114-27-x8x87i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=981&fit=crop&dpr=1 754w, https://images.theconversation.com/files/569190/original/file-20240114-27-x8x87i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=981&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/569190/original/file-20240114-27-x8x87i.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=981&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Artist’s reconstruction of <em>Harajicadectes</em> menacing a pair of armoured <em>Bothriolepis</em>.</span>
<span class="attribution"><span class="source">Artist: Brian Choo</span></span>
</figcaption>
</figure>
<p>The most striking and perhaps most important features are the two huge openings on the top of the skull called spiracles. These typically only appear as minute slits in most early bony fishes.</p>
<p>Similar giant spiracles also appear in <a href="https://en.wikipedia.org/wiki/Gogonasus"><em>Gogonasus</em></a>, a marine tetrapodomorph from the famous Late Devonian Gogo Formation of Western Australia. (It doesn’t appear to be an immediate relative of <em>Harajicadectes</em>.)</p>
<p>They are also seen in the unrelated <a href="https://onlinelibrary.wiley.com/doi/am-pdf/10.1002/spp2.1243"><em>Pickeringius</em></a>, an early ray-finned fish that was also at Gogo.</p>
<h2>The earliest air-breathers?</h2>
<p>Other Devonian animals that sported such spiracles were the famous elpistostegalians – freshwater tetrapodomorphs from the Northern Hemisphere such as <a href="https://en.wikipedia.org/wiki/Elpistostege"><em>Elpistostege</em></a> and <a href="https://en.wikipedia.org/wiki/Tiktaalik"><em>Tiktaalik</em></a>.</p>
<p>These animals were extremely close to the ancestry of limbed vertebrates. So, enlarged spiracles seem to have arisen independently in at least four separate lineages of Devonian fishes.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/567607/original/file-20240102-21-evllkl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/567607/original/file-20240102-21-evllkl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/567607/original/file-20240102-21-evllkl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=628&fit=crop&dpr=1 600w, https://images.theconversation.com/files/567607/original/file-20240102-21-evllkl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=628&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/567607/original/file-20240102-21-evllkl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=628&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/567607/original/file-20240102-21-evllkl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=789&fit=crop&dpr=1 754w, https://images.theconversation.com/files/567607/original/file-20240102-21-evllkl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=789&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/567607/original/file-20240102-21-evllkl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=789&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 skull of <em>Harajicadectes</em> seen from above, showing the enormous spiracles.</span>
<span class="attribution"><span class="source">Author provided</span></span>
</figcaption>
</figure>
<p>The only living fishes with similar structures are bichirs, African ray-finned fishes that live in shallow floodplains and estuaries. It was recently confirmed <a href="https://theconversation.com/now-listen-air-breathing-fish-gave-humans-the-ability-to-hear-21324">they draw surface air through their spiracles</a> to aid survival in oxygen-poor waters.</p>
<p>That these structures appeared roughly simultaneously in four Devonian lineages provides a fossil “signal” for scientists attempting to reconstruct atmospheric conditions in the distant past.</p>
<p>It could help us uncover the evolution of air breathing in backboned animals.</p><img src="https://counter.theconversation.com/content/219397/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Brian Choo receives funding from the Australian Research Council and is employed by Flinders University.</span></em></p><p class="fine-print"><em><span>Alice Clement receives funding from the Australian Research Council and is employed by Flinders University.</span></em></p><p class="fine-print"><em><span>John Long receives funding from The Australian Research Council.</span></em></p>For decades, the sandstone in central Australia yielded tantalising segments of some sort of fossil fish. Now, we have finally pieced together a complete picture of this remarkable species.Brian Choo, Postdoctoral fellow in vertebrate palaeontology, Flinders UniversityAlice Clement, Research Associate in the College of Science and Engineering, Flinders UniversityJohn Long, Strategic Professor in Palaeontology, Flinders UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2123082023-10-17T15:29:28Z2023-10-17T15:29:28ZHow animal traits have shaped the journey of species across the globe<p>The devastating <a href="https://www.ngdc.noaa.gov/hazel/view/hazards/tsunami/event-more-info/5413">tsunami</a> that hit Japan in March 2011 set off a series of events which have long fascinated scientists like me. It was so powerful that it caused 5 million tonnes of debris to <a href="https://marinedebris.noaa.gov/japan-tsunami-marine-debris/monitoring-tsunami-debris-north-american-shorelines">wash</a> into the Pacific – 1.5 million tonnes remained afloat and started drifting with the currents. </p>
<p>One year later, and half a world away, debris began washing ashore on the west coast of North America. More than 280 Japanese coastal species such as mussels, barnacles and even some species of fish, had <a href="https://www.science.org/doi/full/10.1126/science.aao1498?casa_token=YwHfCNElf14AAAAA:zJj4eY3uUm2_m4ZH5YzIO6ecvSWdVa_53yZk0ycnxm1Ga3bPLTl5Z6hCbUhvsmA4d0KSPHFPKz84nQ">hitched a ride</a> on the debris and made an incredible journey across the ocean. These species were still alive and had the potential to establish new populations. </p>
<p>How animals cross major barriers, such as oceans and mountain ranges, to shape Earth’s biodiversity is an intriguing topic. And a new <a href="https://www.nature.com/articles/s41559-023-02150-5">study</a> by my collaborators and I has shed light on this process, revealing how animal characteristics such as body size and life history can influence their spread across the globe.</p>
<p>We know that such dispersal events occur in terrestrial species as well. For instance, at least 15 green iguanas <a href="https://www.nature.com/articles/26886">journeyed</a> more than 200km (124 miles) from Guadeloupe to Anguilla in the Caribbean in 1995. They arrived on a mat of logs and trees (likely uprooted through a hurricane), some of which were more than 9 metres (20 feet) long. </p>
<h2>The role of animal characteristics in dispersal</h2>
<p>When animals move across major barriers it can have a big impact on both the new and old locations. For example, an invasive species can arrive in a new area and compete with native species for resources. However, those consequences can be even greater over longer periods of time.</p>
<p>The movement of monkeys from Africa to South America around 35 million years ago led to the evolution of more than 90 species of <a href="https://www.annualreviews.org/doi/abs/10.1146/annurev-anthro-102116-041510?casa_token=CZtEoQ5Z9bMAAAAA%3AX9JrgVyGxxegDXgVTUPNHZboMldBec1egagn5S4pLwx4yudreF4L6Q6zG4jUeB9tMxJEIy4q67iX&journalCode=anthro">New World monkeys</a>, including tamarins, capuchins and spider monkeys. And a few chameleons rafting on vegetation from Africa to Madagascar is why we find half of all living <a href="https://royalsocietypublishing.org/doi/10.1098/rspb.2013.0184">chameleon</a> species there today.</p>
<p>These events were long thought to be determined by chance – the coincidence of some chameleons sitting on the right tree at the right time. However, <a href="https://www.jstor.org/stable/pdf/24529638.pdf?casa_token=NyxiUsFXod0AAAAA:9aBvrCPO0om98AjWOfs482QWf5eQxRUwKt95p4S3trPy1CQ2CM4K0AJeMBtsNKwKST8ILswcwdjQBRq8ZpdR5-3KL3gOn9uYZHOjzDdPyTm4R3Dom1o">some scientists</a> have suggested there might be more to it. They hypothesised there could be more general patterns in the animals that reach their destination successfully, related to certain characteristics.</p>
<p>Could body size affect how far a species can travel? Animals with more fat reserves may be able to travel longer distances. Or could it be how a species reproduces and survives? For example, animals that lay many eggs or mature early may be more likely to establish a new population in a new place.</p>
<p>But despite a vigorous theoretical debate, the options to test these hypotheses were limited because such dispersal events are rare. Also, the right statistical tools were not available until recently.</p>
<p>Thanks to the recent development of new <a href="https://academic.oup.com/sysbio/article/69/1/61/5490843">biogeographical models</a> and the great availability of data, we can now try to answer questions about how tetrapod species (amphibians, reptiles, birds and mammals) have moved around the globe over the past 300 million years and whether successful species share any common characteristics.</p>
<p>These models allow us to estimate the movements of species’ ancestors while also considering their characteristics. We used these models to study 7,009 species belonging to 56 groups of tetrapods.</p>
<h2>What we found</h2>
<p>For 91% of the animal groups we studied, models that included species characteristics were better supported than models that didn’t. This means that body size and life history are closely linked to how successful a species is at moving to and establishing itself in a new location.</p>
<p>Animals with large bodies and fast life histories (breeding early and often, like water voles) generally dispersed more successfully, as expected. However, there were some exceptions to this rule. In some groups, smaller animals or animals with average traits had higher dispersal rates.</p>
<p>For example, small hummingbirds dispersed better than larger ones, and poison dart frogs with intermediate life histories dispersed better than those with very fast or very slow life histories.</p>
<p>We investigated this variation further and found that the relationship between body size and movement depended on the average size and life history of the group. Our results show that the links between characteristics and dispersal success depend on both body size and life history, and that these cannot be considered separately. </p>
<p>Groups in which small size was an advantage were often already made up of small species (making the dispersal-prone species even smaller), and these species also had fast life histories. We found this to be true for the rodent families <a href="https://www.britannica.com/animal/Muridae"><em>Muridae</em></a> and <a href="https://nhpbs.org/wild/cricetidae.asp"><em>Cricetidae</em></a>. </p>
<p>But groups in which dispersers had intermediate body sizes generally had slow life histories (meaning they had low reproductive output but long lifespans). This means the combination of small body size and slow life history is very unlikely to be an advantage for dispersal across major barriers such as oceans.</p>
<h2>It’s not just chance</h2>
<p>It is amazing to think that rare dispersal events, which can lead to the rise of many new species, are not completely random. Instead, the intrinsic characteristics of species can shape the histories of entire groups of animals, even though chance still may play an important role.</p>
<p>At the same time, two of the most important <a href="https://zenodo.org/record/3553579">environmental challenges</a> of our time are related to movement across major barriers: biological invasions and species’ responses to climate change. On a planet facing rapid changes, understanding how animals move across barriers is therefore crucial.</p><img src="https://counter.theconversation.com/content/212308/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>While working on this study, Sarah-Sophie Weil was affiliated with Université Grenoble Alpes (France) and Swansea University (Wales, UK) who supported her through Initiative d’excellence (IDEX) International Strategic Partnership and Swansea University Strategic Partner Research (SUSPR) scholarships.</span></em></p>New research looks at how different species have managed to cross geographic barriers throughout history and whether their individual traits played a crucial role in these journeys.Sarah-Sophie Weil, PhD candidate, Swansea UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2099192023-07-30T11:15:37Z2023-07-30T11:15:37ZMeet the gigantic extinct reptile that weighed as much as an adult black rhino<figure><img src="https://images.theconversation.com/files/539200/original/file-20230725-29-xonj5i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Three 3D views of _Bradysaurus baini_ specimen (FMNH UC 1533). Scale bar equals 50 cm. [Published in Van den Brandt et al. 2023](https://www.tandfonline.com/doi/full/10.1080/08912963.2023.2175211?journalCode=ghbi20)</span> <span class="attribution"><span class="source">Credit: Fabio Manucci and Marco Romano</span></span></figcaption></figure><p>Around 262 million years ago, during the <a href="https://www.tandfonline.com/doi/abs/10.1080/14772019.2022.2035440">middle Permian Period</a>, a new family of reptiles emerged. Pareiasaurs – meaning “cheek lizards”, a reference to the flat flanges of bone that make up their cheeks – had skulls covered in bony growths and bumps, and bony plates on their bodies.</p>
<p>They were among the first large terrestrial animals to evolve and did so rapidly, quickly becoming some of the most abundant plant-eating animals worldwide. At least <a href="https://www.frontiersin.org/articles/10.3389/fevo.2021.758802/full">21 separate species evolved</a> before all pareiasaurs were wiped out about 252 million years ago during the <a href="https://doi.org/10.25131/sajg.123.0009">Permian-Triassic extinction event</a>.</p>
<p>From the 1830s onward, pareiasaur fossils began to be found in various parts of the world. One large, abundant species, <em>Bradysaurus</em>, from the middle Permian Period, was found in South Africa and <a href="https://royalsocietypublishing.org/doi/10.1098/rstb.1892.0008">scientifically described</a> in 1892. <a href="https://www.frontiersin.org/articles/10.3389/fevo.2021.692035/full"><em>Scutosaurus</em></a>, from the late Permian Period of Russia, was described in 1922.</p>
<p>Thanks to more than 150 years of research, we know that several pareiasaurs were big animals, reaching lengths of up to 3 metres. Their bones reveal that they were thick and stocky. They stood low to the ground, with a primitive sprawling posture. But no accurate studies of their likely body mass exist. </p>
<p>Body mass plays a central role in understanding an organism’s general physiology, ecology, metabolism, diet and movement.</p>
<p>In our <a href="https://www.tandfonline.com/doi/abs/10.1080/08912963.2023.2175211?journalCode=ghbi20">new study</a>, we set out to fill this knowledge gap for <em>Bradysaurus</em>, having done so for <em>Scutosaurus</em> in <a href="https://www.frontiersin.org/articles/10.3389/fevo.2021.692035/full">another piece of work</a>. We used a new method for calculating body mass that allowed us to calculate the <em>Bradysaurus</em> had a likely overall average body mass of 1,022kg. </p>
<p>For the Russian <em>Scutosaurus</em>, <a href="https://www.frontiersin.org/articles/10.3389/fevo.2021.692035/full">we found</a> an average body mass of 1,160kg. That means both of these pareiasaurs, from different hemispheres and living in different times, weighed in at about the mass of a large adult black rhino or a large domestic bull.</p>
<p><em>Bradysaurus</em> is the oldest pareiasaur that has been reliably dated. It was one of the earliest huge plant-eating tetrapods (four-legged creatures) to appear in the development of life on Earth, along with other large pareiasaur species like <em>Scutosaurus</em>. By obtaining accurate body mass estimates for these animals, we can better understand the evolution of the said body mass, which was built around a long intestinal track inside a huge fermentation chamber – just what the animals needed to break down high volumes of poor quality vegetation.</p>
<h2>A new method</h2>
<p>Typically, the body masses of extinct tetrapods are estimated using mathematical formulas that relate the circumferences of the thigh bone (the femur) and the upper arm bone (the humerus) to body mass. </p>
<p>These formulas were derived from large sets of measurements of the limb bones of modern animals whose masses can be measured directly. </p>
<p>But, as palaeontologist Marco Romano has <a href="https://www.idunn.no/doi/full/10.1111/let.12207">detailed</a> in <a href="https://www.tandfonline.com/doi/abs/10.1080/08912963.2019.1640219">several studies</a>, using these <a href="https://www.frontiersin.org/articles/10.3389/fevo.2021.692035/full">formulas</a> tends to <a href="https://www.tandfonline.com/doi/abs/10.1080/08912963.2023.2175211?journalCode=ghbi20">result</a> in hugely inflated overestimates of body mass when they are applied to extinct reptiles. These animals often had a sprawling posture and, as a result, thickened bones. Modern mammals have upright postures and relatively slender limb bones. </p>
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<p>We used a new volumetric method to determine a more realistic mass estimate. First, 3D models of skeletons were made using photogrammetry. Nearly 200 photographs were taken around each skeleton, then digitally combined in specialist software to create accurate 3D models of the bones. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/539201/original/file-20230725-25-kjdcs1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/539201/original/file-20230725-25-kjdcs1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=646&fit=crop&dpr=1 600w, https://images.theconversation.com/files/539201/original/file-20230725-25-kjdcs1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=646&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/539201/original/file-20230725-25-kjdcs1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=646&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/539201/original/file-20230725-25-kjdcs1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=811&fit=crop&dpr=1 754w, https://images.theconversation.com/files/539201/original/file-20230725-25-kjdcs1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=811&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/539201/original/file-20230725-25-kjdcs1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=811&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Artistic <em>in vivo</em> reconstruction of <em>Bradysaurus baini</em> specimen (FMNH UC 1533) based on the 3D ‘average’ model sculpted around the specimen, in five views. Scale bar equals 50 cm. Published in Van den Brandt et al. 2023.</span>
<span class="attribution"><span class="source">Credit: Fabio Manucci and Marco Romano</span></span>
</figcaption>
</figure>
<p>Next, palaeoartist Fabio Manucci used other specialist software to model soft tissue, muscles and guts around the bones, creating three reconstructions of possible volumes (“slim”, “average”, “fat”) for each skeleton by adding three different amounts of soft tissue.</p>
<p>The average density of both extinct and living vertebrate animals is very close to the density of water (1kg per litre). The denser bones and tissues are balanced out by empty spaces such as <a href="https://anatomypubs.onlinelibrary.wiley.com/doi/full/10.1002/ar.24574">air in the lungs and guts</a>. Extinct pareiasaurs were probably a bit more dense because of their very thick bones and plated, bony body armour.</p>
<p>To determine a range of masses, we applied three different densities for living tissues (0.99kg, 1kg and 1.15kg/litre) to each of our slim, average and fat volumes to calculate possible body masses.</p>
<p>The estimates we obtained differed from those obtained using two popular existing formulas based on modern mammals and non-avian reptiles’ limb bone measurements. For <em>Bradysaurus</em>, the two formulas exceeded our volumetric estimates by up to 375%, suggesting a mass of close to 4 tonnes. For <em>Scutosaurus</em>, the figure was up to 235% higher than our results. </p>
<p>These high mass estimates seem highly unlikely. If they were accurate, the density of the animal’s tissues would have been greater than sandstone or concrete.</p>
<h2>Body size in herbivores</h2>
<p>Now that we have what we believe is an accurate estimate of two pareiasaur species’ body mass, what does it tell us?</p>
<p>The fossil record suggests a rapid increase in body size between the time when their (likely small) ancestors diverged from other early reptiles and the first appearance of <em>Bradysaurus</em> in the fossil record about 262 million years ago.</p>
<p><em>Bradysaurus’s</em> large size is best explained by a negative relationship between food digestibility and body mass. In ecology, this is known as the <a href="https://academic.oup.com/biolinnean/article/115/1/173/2440439?login=false">Jarman-Bell</a> principle. It predicts the evolution of large body size in herbivores that ingest copious, low-quality plant material. Plants are hard to digest, and a plant-based diet typically results in a large body size – herbivores are typically substantially heavier than other dietary groups in living animals. </p>
<p>Alternatively, or maybe in conjunction with the evolution of herbivory, the large body size of <em>Bradysaurus</em> may also have evolved as protection from co-existing predators. Pareiasaurian body armour and their large cheek flanges also suggest adaptations developed as protection from common predators, which would be especially useful for these slow moving, stocky herbivores.</p><img src="https://counter.theconversation.com/content/209919/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Marc Johan Van den Brandt receives funding from the University of the Witwatersrand, GENUS (DSI-NRF Centre of Excellence in Palaeosciences, UID 86073), and the Millenium Trust.</span></em></p><p class="fine-print"><em><span>Kenneth D. Angielczyk receives funding from the U.S. National Science Foundation and the Field Museum of Natural History. </span></em></p><p class="fine-print"><em><span>Marco Romano 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>Large pareiasaurs are among the earliest huge plant-eating tetrapods to appear in the history of the development of life on Earth.Marc Johan Van den Brandt, Postdoctoral Research Fellow at the Evolutionary Studies Institute (ESI), University of the Witwatersrand, Johannesburg., University of the WitwatersrandKenneth D. Angielczyk, Lecturer, University of ChicagoMarco Romano, Professor of Paleontology, Sapienza University of RomeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1861162022-07-20T15:03:08Z2022-07-20T15:03:08ZMeet Qikiqtania, a fossil fish with the good sense to stay in the water while others ventured onto land<figure><img src="https://images.theconversation.com/files/474947/original/file-20220719-12-fg9agl.jpg?ixlib=rb-1.1.0&rect=4%2C350%2C2686%2C1847&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An artist's vision of *Qikiqtania* enjoying its fully aquatic, free-swimming lifestyle.</span> <span class="attribution"><span class="source">Alex Boersma</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>Approximately 365 million years ago, one group of fishes left the water to live on land. These animals were early <a href="https://ucmp.berkeley.edu/vertebrates/tetrapods/tetraintro.html">tetrapods</a>, a lineage that would radiate to include many thousands of species including amphibians, birds, lizards and mammals. Human beings are descendants of those early tetrapods, and we share the legacy of their water-to-land transition.</p>
<p>But what if, instead of venturing onto the shores, they had turned back? What if these animals, just at the cusp of leaving the water, had receded to live again in more open waters?</p>
<p><a href="https://www.nature.com/articles/s41586-022-04990-w">A new fossil</a> suggests that one fish, in fact, did just that. In contrast to other closely related animals, which were using their fins to prop their bodies up on the bottom of the water and perhaps occasionally venturing out onto land, this newly discovered creature had fins that were built for swimming.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/474195/original/file-20220714-9624-3szicz.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="seated man manipulating a stone above a box" src="https://images.theconversation.com/files/474195/original/file-20220714-9624-3szicz.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/474195/original/file-20220714-9624-3szicz.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/474195/original/file-20220714-9624-3szicz.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/474195/original/file-20220714-9624-3szicz.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/474195/original/file-20220714-9624-3szicz.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/474195/original/file-20220714-9624-3szicz.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/474195/original/file-20220714-9624-3szicz.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">Tom Stewart holds the <em>Qikiqtania</em> fossil.</span>
<span class="attribution"><span class="source">Stephanie Sang</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<p>In March 2020, I was at The University of Chicago and a member of biologist <a href="https://oba.bsd.uchicago.edu/faculty/neil-h-shubin-phd">Neil Shubin’s</a> lab. I was working with Justin Lemberg, another researcher in our group, to process a fossil that was collected back in 2004 during an expedition to the Canadian Arctic.</p>
<p>From the surface of the rock it was embedded in, we could see fragments of the jaws, about 2 inches long (5 cm) and with pointed teeth. There were also patches of white scales with bumpy texture. The anatomy gave us subtle hints that the fossil was an early tetrapod. But we wanted to see inside the rock.</p>
<p>So we used a technology called CT scanning, which shoots X-rays through the specimen, to look for anything that might be hidden within, out of view. On March 13, we scanned an unassuming piece of rock that had a few scales on top and discovered it contained a complete fin buried inside. Our jaws dropped. A few days later, the lab and campus shut down, and COVID-19 sent us into lockdown.</p>
<h2>The fin revealed</h2>
<p>A fin like this is extremely precious. It can give scientists clues into how early tetrapods were evolving and how they were living hundreds of millions of years ago. For example, based on the shape of certain bones in the skeleton, we can make predictions about whether an animal was swimming or walking. </p>
<p>Although that first scan of the fin was promising, we needed to see the skeleton in high resolution. As soon as we were allowed back on campus, a professor in the university’s department of the geophysical sciences helped us to trim down the block using a rock saw. This made the block more fin, less rock, allowing for a better scan and a closer view of the fin.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/aRCdHHe2yfw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">An animation of the pectoral fin of <em>Qikiqtania</em> showing how it was preserved in the rock. Scales are shown in yellow, fin rays in blue, and the endoskeleton in grey. <em>Credit: Tom Stewart</em></span></figcaption>
</figure>
<p>When the dust had cleared and we’d finished analyzing data on the jaws, scales and fin, we realized that this animal was a new species. Not only that, it turns out that this is one of the closest known relatives to limbed vertebrates – those creatures with fingers and toes.</p>
<p>We named it <em>Qikiqtania wakei</em>. Its genus name, pronounced “kick-kiq-tani-ahh,” refers to the Inuktitut words Qikiqtaaluk or Qikiqtani, the traditional name for the <a href="https://en.wikipedia.org/wiki/Qikiqtaaluk_Region">region where the fossil was found</a>. When this fish was alive, many hundreds of millions of years ago, this was a warm environment with rivers and streams. Its species name honors the late <a href="https://www.nytimes.com/2021/05/19/science/david-wake-dead.html">David Wake</a>, a scientist and mentor who inspired so many of us in the field of evolutionary and developmental biology.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/qCEYP08Q-bw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">An animation of the full skeleton of <em>Qikiqtania</em>. <em>Credit: Tom Stewart</em></span></figcaption>
</figure>
<h2>Skeletons tell how an animal lived</h2>
<p><em>Qikiqtania</em> reveals a lot about a critical period in our lineage’s history. Its scales tell researchers unambiguously that it was living underwater. They show sensory canals that would have allowed the animal to detect the flow of water around its body. Its jaws tell us that it was foraging as a predator, biting and holding onto prey with a series of fangs and drawing food into its mouth by suction.</p>
<p>But it is <em>Qikiqtania</em>’s pectoral fin that is most surprising. It has a humerus bone, just as our upper arm does. But <em>Qikiqtania</em>’s has a very peculiar shape.</p>
<p>Early tetrapods, like <a href="https://shubinlab.uchicago.edu/research-2-2/"><em>Tiktaalik</em></a>, have humeri that possess a prominent ridge on the underside and a characteristic set of bumps, where muscles attach. These bony bumps tell us that early tetrapods were living on the bottom of lakes and streams, using their fins or arms to prop themselves up, first on the ground underwater and later on land.</p>
<p><em>Qikiqtania</em>’s humerus is different. It lacks those trademark ridges and processes. Instead, its humerus is thin and boomerang-shaped, and the rest of the fin is large and paddle-like. This fin was built for swimming.</p>
<p>Whereas other early tetrapods were playing at the water’s edge, learning what land had to offer, <em>Qikiqtania</em> was doing something different. Its humerus is truly unlike any others known. My colleagues and I think it shows that <em>Qikiqtania</em> had turned back from the water’s edge and evolved to live, once again, off the ground and in open water.</p>
<h2>Evolution isn’t a march in one direction</h2>
<p><a href="https://plato.stanford.edu/entries/evolution/">Evolution isn’t a simple, linear process</a>. Although it might seem like early tetrapods were trending inevitably toward life on land, <em>Qikiqtania</em> shows exactly the limitations of such a directional perspective. Evolution didn’t build a ladder towards humans. It’s a complex set of processes that together grow the tangled tree of life. New species form and they diversify. Branches can head off in any number of directions.</p>
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<a href="https://images.theconversation.com/files/471997/original/file-20220701-22-xozchf.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Man standing on rocky flat ground with mountains in the distance" src="https://images.theconversation.com/files/471997/original/file-20220701-22-xozchf.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/471997/original/file-20220701-22-xozchf.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=406&fit=crop&dpr=1 600w, https://images.theconversation.com/files/471997/original/file-20220701-22-xozchf.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=406&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/471997/original/file-20220701-22-xozchf.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=406&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/471997/original/file-20220701-22-xozchf.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=511&fit=crop&dpr=1 754w, https://images.theconversation.com/files/471997/original/file-20220701-22-xozchf.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=511&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/471997/original/file-20220701-22-xozchf.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=511&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Neil Shubin, who found the fossil, pointing across the valley to the site where <em>Qikiqtania</em> was discovered on Ellesmere Island.</span>
<span class="attribution"><span class="source">Neil Shubin</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>This fossil is special for so many reasons. It’s not just miraculous that this fish was preserved in rock for hundreds of millions of years before being discovered by scientists in the Arctic, on <a href="https://en.wikipedia.org/wiki/Ellesmere_Island">Ellesmere Island</a>. It’s not just that it’s remarkably complete, with its full anatomy revealed by serendipity at the cusp of a global pandemic. It also provides, for the first time, a glimpse of the broader diversity and range of lifestyles of fishes at the water-to-land transition. It helps researchers see more than a ladder and understand that fascinating, tangled tree.</p>
<h2>Discoveries depend on community</h2>
<p><em>Qikiqtania</em> was found on Inuit land, and it belongs to that community. My colleagues and I were only able to conduct this research because of the generosity and support of individuals in the hamlets of Resolute Bay and Grise Fiord, the Iviq Hunters and Trappers of Grise Fiord, and the Department of Heritage and Culture, Nunavut. To them, on behalf of our entire research team, “nakurmiik.” Thank you. Paleontological expeditions onto their land have truly changed how we understand the history of life on Earth.</p>
<p>COVID-19 kept many paleontologists from traveling and visiting field sites across the world these last few years. We’re eager to return, to visit with old friends and to search again. Who knows what other animals lie hidden, waiting to be discovered inside blocks of unassuming stone.</p><img src="https://counter.theconversation.com/content/186116/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Thomas Stewart 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>The newly discovered species – Qikiqtania – highlights evolution’s twisty, tangled path.Thomas Stewart, Assistant Professor of Biology, Penn StateLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1574182021-03-20T00:01:10Z2021-03-20T00:01:10ZWhen our evolutionary ancestors first crawled onto land, their brains only half-filled their skulls<figure><img src="https://images.theconversation.com/files/390639/original/file-20210319-23-q4umh9.jpg?ixlib=rb-1.1.0&rect=271%2C271%2C6438%2C4194&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>Most of us would recognise a human brain, but what about the brain of a frog or fish? Given the vast diversity of life on Earth, there are some weird and wonderful brains out there. </p>
<p>Despite this, the basic plan of most <a href="https://en.wikipedia.org/wiki/Vertebrate">vertebrate</a> (animals with a backbone) brains is similar, consisting of three major regions: the fore-, mid- and hindbrain. But the variation in size and shape between these regions (and others) is what makes studying vertebrates so fascinating. </p>
<p>Research published today by my colleagues and me in <a href="https://www.frontiersin.org/articles/10.3389/fevo.2021.640345/full">Frontiers in Ecology and Evolution</a> indicates some of our earliest ancestors — which were likely still taking their first steps on land — had brains that only filled about half the space in their skulls.</p>
<h2>The hurdles of studying ancient brains</h2>
<p>Growing and maintaining brain tissue is energetically expensive for animals. The relative size of different regions of the brain is thought to be guided by a <a href="https://www.journals.uchicago.edu/doi/abs/10.1086/201571?journalCode=ca">concept known as</a> “the principle of proper mass”. </p>
<p>This states the more important a sense or brain region is to an animal, the more likely it is that region will be enlarged compared to others. After all, it’s pointless to spend lots of energy growing a visual processing centre if you’re a blind, cave-dwelling animal.</p>
<p>While studying the brains of living beasts is straightforward, this is much more complicated for extinct animals. When organisms fossilise, their soft tissues (including the muscle and brain) tend to decompose quickly, leaving only the hard parts of the skeleton to be preserved. </p>
<p>This means experts have to study the internal parts of the skull (or the “<a href="https://en.wikipedia.org/wiki/Neurocranium">braincase</a>”) and the void within it, which is called an “<a href="https://en.wikipedia.org/wiki/Endocast#:%7E:text=An%20endocast%20is%20the%20internal,may%20occur%20naturally%20through%20fossilization.">endocast</a>”. <a href="https://en.wikipedia.org/wiki/Paleoneurobiology">Palaeoneurology</a> is the study of endocasts and fossil brains. This field was founded about a century ago by palaeontologist <a href="https://www.smithsonianmag.com/science-nature/woman-who-shaped-study-fossil-brains-180968254/">Tilly Edinger</a>. </p>
<p>In palaeoneurology’s early days, scientists had to rely on lucky discoveries of skulls cracked in half to reveal the inside, or they had to destroy specimens to create an endocast. These days, researchers can use advanced scanning methods to create endocasts digitally, without damaging the specimen.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/a-new-brain-warp-technique-that-helps-to-reconstruct-fossil-brains-61423">A new brain-warp technique that helps to reconstruct fossil brains</a>
</strong>
</em>
</p>
<hr>
<h2>The tremendous tetrapod transition</h2>
<p>Today, half of all vertebrate life can be classified as <a href="https://en.wikipedia.org/wiki/Tetrapod">tetrapods</a> — backboned animals with four limbs bearing digits (fingers and toes). This includes humans, frogs, crocodiles, parrots and kangaroos, among many, many others.</p>
<p>The animals responsible for giving rise to this huge array are known as “stem tetrapods”. These brave beasts first ventured out of the water and onto land more than 360 million years ago. </p>
<p>For fish to transition into land-dwelling tetrapods required many changes to their body and brain. Fins made way for limbs, and gills gave way to lungs that could breathe air. What’s more, the terrestrial realm would have presented an entirely new sensory environment to navigate. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/390307/original/file-20210318-23-dnatl1.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Silhouettes of fish and tetrapods in water and on land." src="https://images.theconversation.com/files/390307/original/file-20210318-23-dnatl1.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/390307/original/file-20210318-23-dnatl1.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=358&fit=crop&dpr=1 600w, https://images.theconversation.com/files/390307/original/file-20210318-23-dnatl1.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=358&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/390307/original/file-20210318-23-dnatl1.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=358&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/390307/original/file-20210318-23-dnatl1.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=449&fit=crop&dpr=1 754w, https://images.theconversation.com/files/390307/original/file-20210318-23-dnatl1.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=449&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/390307/original/file-20210318-23-dnatl1.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=449&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 various environments inhabited by animals spanning the fish-tetrapod transition would have favoured different types of brains.</span>
<span class="attribution"><span class="source">Author provided</span></span>
</figcaption>
</figure>
<p>How did the brains of stem tetrapods change in response to this major ecological shift? </p>
<p>We have some clues gleaned from skeleton parts, such as enlarged eye sockets that coincide with the transition from fish to tetrapods on land. One <a href="https://www.pnas.org/content/114/12/E2375.short">study</a> has suggested a change in eye position and size would have led to a million-fold increase in visual acuity in early tetrapods, compared with their fishy relatives. </p>
<p>If so, we would expect such changes to be reflected in the visual processing regions of the brain. But how can we test this? </p>
<h2>Interpreting ancient endocasts</h2>
<p>One of the trickiest things about interpreting endocasts is that not all brains fill the endocast space fully. While most birds and mammals have brains that closely match the shape of the endocast, other animals such as fish, amphibians and reptiles typically don’t. </p>
<p>In fact, the coelacanth fish is famous for having an extremely tiny brain that takes up just 1% of its endocast. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/390549/original/file-20210319-21-17qsci7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Latimeria with black background" src="https://images.theconversation.com/files/390549/original/file-20210319-21-17qsci7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/390549/original/file-20210319-21-17qsci7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/390549/original/file-20210319-21-17qsci7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/390549/original/file-20210319-21-17qsci7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/390549/original/file-20210319-21-17qsci7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/390549/original/file-20210319-21-17qsci7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/390549/original/file-20210319-21-17qsci7.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">Coelacanths are a rare order of fish that includes two species in the genus Latimeria.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/we-scanned-one-of-our-closest-cousins-the-coelacanth-to-learn-how-its-brain-grows-115147">We scanned one of our closest cousins, the coelacanth, to learn how its brain grows</a>
</strong>
</em>
</p>
<hr>
<p>I’ve been studying the spatial relationship between the brain and endocast in animals that fall into a category called the stem tetrapod “<a href="https://en.wikipedia.org/wiki/Phylogenetic_bracketing">extant phylogenetic bracket</a>”. These are the closest living relatives of the extinct stem tetrapods in the evolutionary tree.</p>
<p>This category includes the coelacanth fish, lungfishes and amphibians such as frogs, salamanders and caecilians. </p>
<p>Using a scanning method referred to as <a href="https://dicect.com/">diceCT</a>, we scanned the heads of these animals and measured the brains within to compare the brain’s size and shape with that of the endocast.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/390310/original/file-20210318-19-kix05b.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/390310/original/file-20210318-19-kix05b.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/390310/original/file-20210318-19-kix05b.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=230&fit=crop&dpr=1 600w, https://images.theconversation.com/files/390310/original/file-20210318-19-kix05b.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=230&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/390310/original/file-20210318-19-kix05b.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=230&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/390310/original/file-20210318-19-kix05b.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=289&fit=crop&dpr=1 754w, https://images.theconversation.com/files/390310/original/file-20210318-19-kix05b.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=289&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/390310/original/file-20210318-19-kix05b.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=289&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Brains (pink) and endocasts (grey) of animals spanning the fish-tetrapod transition.</span>
<span class="attribution"><span class="source">Author provided</span></span>
</figcaption>
</figure>
<p>A series of papers published by myself and my colleagues have shown lungfish, unlike the coelacanth, have brains that fill a <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0141277">far greater portion of their endocast</a> (starting from about 40% and possibly up to 80%).</p>
<p>Within amphibians, salamander brains <a href="https://royalsocietypublishing.org/doi/full/10.1098/rsos.200933">looked quite similar to lungfish brains</a> and filled their endocasts in a similar way. </p>
<p>In our most recent paper, however, we investigated frogs and caecilians and found they have brains that are generally more tightly fitted inside their endocasts.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/390553/original/file-20210319-16-77avyp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="dd" src="https://images.theconversation.com/files/390553/original/file-20210319-16-77avyp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/390553/original/file-20210319-16-77avyp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=402&fit=crop&dpr=1 600w, https://images.theconversation.com/files/390553/original/file-20210319-16-77avyp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=402&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/390553/original/file-20210319-16-77avyp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=402&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/390553/original/file-20210319-16-77avyp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=505&fit=crop&dpr=1 754w, https://images.theconversation.com/files/390553/original/file-20210319-16-77avyp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=505&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/390553/original/file-20210319-16-77avyp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=505&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Caecilians are a limbless amphibian that lives in moist underground soil and forest streams.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<h2>Reconstructing old brains</h2>
<p>This knowledge helps us more accurately estimate the likely brain sizes of extinct stem tetrapods. Also, considering the ecology and habitats of the living relatives helps us further narrow down these values. </p>
<p>For instance, frogs and caecilians are highly specialised amphibians and are therefore unlikely to accurately represent the biology of the first tetrapods. Similarly, the coelacanth is a deep-water marine fish, whereas the earliest tetrapods lived in shallow and marginal environments. </p>
<p>This leaves us with salamanders and lungfish as the best living examples of what the neural biology of the first tetrapods may have looked like. With this in mind, we can reasonably assume the brains of our early ancestors that took those first steps onto land filled about 40-50% of their endocasts — with the rest likely full of fatty tissue or fluid.</p>
<p>Combining this with <a href="https://theconversation.com/when-fish-gave-us-the-finger-this-ancient-four-limbed-fish-reveals-the-origins-of-the-human-hand-129072">spectacular 3D-preserved fossils</a>, we can begin to reconstruct the brains of these animals from millions of years ago.</p>
<p>Moreover, understanding how their brains changed during the vital juncture from water to land will help us understand a giant step in our own neural evolutionary history. </p>
<hr>
<p><em>Acknowledgement: <a href="https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0141277">Research</a> <a href="https://royalsocietypublishing.org/doi/full/10.1098/rsos.200933">referenced</a> in this article was conducted in collaboration with Prof. John Long and Ms. Corinne Mensforth from Flinders University, Prof. Shaun Collin from La Trobe University, and Dr Tom Challands from The University of Edinburgh (UK).</em></p><img src="https://counter.theconversation.com/content/157418/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Dr Alice Clement receives funding from The Australian Research Council. </span></em></p>‘Tetrapods’ were the first fish to evolve lungs and walk onto land. They were also our ancestors. Now, a new study sheds light on the size and shape of these unique animals’ brains.Alice Clement, Research Associate in the College of Science and Engineering, Flinders UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1462482020-09-16T18:29:13Z2020-09-16T18:29:13ZNewly discovered mass extinction event triggered the dawn of the dinosaurs<figure><img src="https://images.theconversation.com/files/358163/original/file-20200915-20-15gp9vz.jpg?ixlib=rb-1.1.0&rect=49%2C155%2C1930%2C915&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">D. Bonadonna/ MUSE, Trento</span>, <span class="license">Author provided</span></span></figcaption></figure><p>Huge volcanic eruptions 233 million years ago pumped carbon dioxide, methane and water vapour into the atmosphere. This series of violent explosions, on what we now know as the west coast of Canada, led to massive global warming. Our <a href="https://advances.sciencemag.org/content/advances/6/38/eaba0099.full.pdf">new research</a> has revealed that this was a planet-changing mass extinction event that killed off many of the dominant tetrapods and heralded the dawn of the dinosaurs. </p>
<p>The best known mass extinction happened at the end of the Cretaceous period, 66 million years ago. This is when dinosaurs, <a href="https://theconversation.com/pterosaurs-should-have-been-too-big-to-fly-so-how-did-they-manage-it-60892">pterosaurs</a>, marine reptiles and ammonites all died out. This event was caused primarily by the impact of a giant asteroid that blacked out the light of the sun and caused darkness and freezing, followed by other massive perturbations of the oceans and atmosphere.</p>
<p>Geologists and palaeontologists agree on a roster of five such events, of which the end-Cretaceous mass extinction was the last. So our new discovery of a previously unknown mass extinction might seem unexpected. And yet this event, termed the Carnian Pluvial Episode (CPE), seems to have killed as many species as the giant asteroid did. Ecosystems on land and sea were profoundly changed, as the planet got warmer and drier. </p>
<figure class="align-center ">
<img alt="An erupting volcano." src="https://images.theconversation.com/files/358352/original/file-20200916-14-10ku33l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/358352/original/file-20200916-14-10ku33l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/358352/original/file-20200916-14-10ku33l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/358352/original/file-20200916-14-10ku33l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/358352/original/file-20200916-14-10ku33l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/358352/original/file-20200916-14-10ku33l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/358352/original/file-20200916-14-10ku33l.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">
<figcaption>
<span class="caption">Huge volcanic eruptions changed life on Earth 233 million years ago.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/volcano-erupting-lava-volcan-landscape-tungurahua-90131104">Sutterstock/AmmitJack</a></span>
</figcaption>
</figure>
<p>On land, this triggered profound changes in plants and herbivores. In turn, with the decline of the dominant plant-eating tetrapods, such as rhynchosaurs and dicynodonts, the dinosaurs were given their chance. </p>
<p>The dinosaurs had originated some 15 million years earlier and <a href="https://advances.sciencemag.org/content/advances/6/38/eaba0099.full.pdf">our new study</a> shows that, as a result of the CPE, they expanded rapidly in the subsequent 10 million to 15 million years and became the dominant species in the terrestrial ecosystems. The CPE triggered the “age of the dinosaurs” which lasted for a further 165 million years.</p>
<p>It wasn’t only the dinosaurs that were given a foothold. Many modern tetrapod groups, such as turtles, lizards, crocodiles and mammals date back to this newly discovered time of revolution.</p>
<h2>Following the clues</h2>
<p>This event was first noticed independently back in the 1980s. But it was thought that it was restricted to Europe. First, geologists in Germany, Switzerland and Italy recognised a major turnover among marine faunas about 232 million years ago, termed the Rheingraben event. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/five-mass-extinctions-and-what-we-can-learn-from-them-about-the-planet-today-79971">Five mass extinctions – and what we can learn from them about the planet today</a>
</strong>
</em>
</p>
<hr>
<p><a href="https://www.nature.com/articles/321857a0">Then in 1986</a>, I recognised this independently as a global-scale turnover among tetrapods and ammonites. But at that time, the age dating was much weaker than now and it was impossible to be sure whether these were both the same event.</p>
<p>The jigsaw pieces started falling into place when an episode of about 1 million years of humid climates was recognised throughout the UK and parts of Europe by geologists <a href="https://pubs.geoscienceworld.org/gsa/geology/article/17/3/265/204901?casa_token=W6hhoQX7ZP0AAAAA:Fz17Rarsuqi6pLf3Scv69a4VKPKEVChkHSB4yNFMefAcGMTRIs0nPc4r3jrf9CZhkuq--3g">Mike Simms and Alastair Ruffell</a>. Then geologist <a href="https://environment.leeds.ac.uk/see/staff/1221/dr-jacopo-dal-corso">Jacopo dal Corso</a> spotted a coincidence in timing of the CPE with the peak of <a href="https://www.sciencedirect.com/science/article/pii/S0921818115000296?casa_token=q8kb-2NBaU0AAAAA:swvCyd1pE2P39_hETqmochWBfrYO1iVV3P8Si0cYsUjbJSovjHcAiCxubnnZ4hPeFHfN3F_UAUs">eruptions of the Wrangellia basalts</a>. </p>
<p>Wrangellia is a term geologists give to a narrow tectonic plate that is attached to the west coast of the North American continent, north of Vancouver and Seattle. </p>
<figure class="align-center ">
<img alt="Map highlighting Wrangellia flood basalts" src="https://images.theconversation.com/files/358353/original/file-20200916-20-133i4kh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/358353/original/file-20200916-20-133i4kh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=596&fit=crop&dpr=1 600w, https://images.theconversation.com/files/358353/original/file-20200916-20-133i4kh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=596&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/358353/original/file-20200916-20-133i4kh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=596&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/358353/original/file-20200916-20-133i4kh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=749&fit=crop&dpr=1 754w, https://images.theconversation.com/files/358353/original/file-20200916-20-133i4kh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=749&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/358353/original/file-20200916-20-133i4kh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=749&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Map showing the distribution of Wrangellia flood basalts in Alaska, Yukon and British Columbia.</span>
<span class="attribution"><a class="source" href="https://www.eoas.ubc.ca/research/wrangellia/1wrang.html">University of British Columbia (EOAS)</a></span>
</figcaption>
</figure>
<p>Finally, in a review of the evidence from <a href="https://www.cambridge.org/core/journals/geological-magazine/article/carnian-humid-episode-of-the-late-triassic-a-review">Triassic-aged rocks</a>, the signature of the CPE was detected – not only in Europe, but also in South America, North America, Australia and Asia. This was far from being a Europe-only event. It was global.</p>
<h2>Volcanic eruptions</h2>
<p>The massive Wrangellia eruptions pumped carbon dioxide, methane and water vapour into the atmosphere, leading to global warming and an increase in rainfall worldwide. There were as many as five pulses of eruptions associated with warming peaks from 233 million years ago. The eruptions led to acid rain as the volcanic gases mixed with rainwater to shower the Earth in dilute acid. Shallow oceans also became acidified. </p>
<p>The sharp warming drove plants and animals from the tropics and the acid rain killed plants on land, while <a href="https://theconversation.com/ocean-acidification-is-chemistry-not-conjecture-15497">ocean acidification</a> attacked all marine organisms with carbonate skeletons. This stripped away the surfaces of the oceans and the land. Life may have begun to recover, but when the eruptions ceased, temperatures remained high while the tropical rainfall ceased. This is what caused the subsequent drying of the land on which the dinosaurs flourished.</p>
<p>Most extraordinary was the re-casting of the marine carbonate factory. This is the global mechanism by which calcium carbonate forms great thicknesses of limestones and provides material for organisms like corals and molluscs to build their shells. The CPE marked the start of modern coral reefs, as well as many of the modern groups of plankton, suggesting profound changes in ocean chemistry. </p>
<figure class="align-center ">
<img alt="Timeline illustration of mass extinction events" src="https://images.theconversation.com/files/358349/original/file-20200916-24-sz016q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/358349/original/file-20200916-24-sz016q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=343&fit=crop&dpr=1 600w, https://images.theconversation.com/files/358349/original/file-20200916-24-sz016q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=343&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/358349/original/file-20200916-24-sz016q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=343&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/358349/original/file-20200916-24-sz016q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=431&fit=crop&dpr=1 754w, https://images.theconversation.com/files/358349/original/file-20200916-24-sz016q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=431&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/358349/original/file-20200916-24-sz016q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=431&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A timeline of mass extinction events.</span>
<span class="attribution"><span class="source">D. Bonadonna/MUSE, Trento</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Before the CPE, the main source of carbonate in the oceans came from microbial ecosystems, such as limestone-dominated mud mounds, on continental shelves. But after the CPE, it was driven by coral reefs and plankton, where new groups of micro-organisms, such as <a href="https://ucmp.berkeley.edu/protista/dinoflagellata.html">dinoflagellates</a>, appeared and bloomed. This profound switch in fundamental chemical cycles in the oceans marked the beginning of modern marine ecosystems.</p>
<p>And there are going to be important lessons for how we help our planet recover from climate change. Geologists need to investigate the details of the Wrangellia volcanic activity and understand how these repeated eruptions drove the climate and changed the Earth’s ecosystems. There have been a number of volcanically-induced mass extinctions in the history of the Earth and the physical perturbations, such as global warming, acid rain and ocean acidification, are among the challenges we see today.</p>
<p>Palaeontologists will need to work more closely on the data from marine and continental fossil records. This will help us understand how the crisis played out in terms of the loss of biodiversity, but also to explore how the planet recovered.</p><img src="https://counter.theconversation.com/content/146248/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Michael J. Benton receives funding from the Natural Environment Research Council (UK) and the European Research Council.</span></em></p>Our new research has discovered how a series of volcanic eruptions 233 million years ago fundamentally changed life on Earth.Michael J. Benton, Professor of Vertebrate Palaeontology, University of BristolLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1381032020-05-26T17:07:42Z2020-05-26T17:07:42ZA fossil discovery reveals the earliest relative of modern mammals<figure><img src="https://images.theconversation.com/files/337684/original/file-20200526-106853-rggnqc.jpg?ixlib=rb-1.1.0&rect=8%2C0%2C2835%2C2136&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Joggins Fossil Cliffs in Nova Scotia are a unique and rich site for preserved fossils.</span> <span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Joggins_Formation#/media/File:Joggins_Fossil_Cliffs,_Joggins,_Nova_Scotia_01.jpg">(Gorob)</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Over 300 million years ago, our ancestors diverged from the ancestors of reptiles and began the evolutionary journey towards becoming mammals. </p>
<p>What were these earliest ancestors like? For one, they looked nothing like modern mammals. The group known as <a href="https://www.britannica.com/animal/Synapsida">synapsids</a> — described as “mammal-like reptiles” — looked much more like reptiles but could be distinguished by a single large opening in the cheek, likely for jaw muscles. Synapsids slowly ascended to the top of the food chain, but we still know very little about the first 10 million years of synapsid evolution.</p>
<p>As PhD candidates in paleontology, we were all working on different aspects of early tetrapod — four-footed animals — evolution. The three of us led a diverse research team that revisited some fossils which had been described as an early reptile named <em>Asaphestera</em>, collected in Nova Scotia. Our study led to a number of surprising results, <a href="https://doi.org/10.1002/spp2.1316">the most significant of which is our identification of <em>Asaphestera</em> as the earliest definitive synapsid fossil</a>.</p>
<h2>Joggins, a UNESCO World Heritage site</h2>
<p>Originally named Chegoggin by the Mi’kmaq people, the <a href="https://jogginsfossilcliffs.net/">fossil cliffs at Joggins, N.S.</a>, preserve the remains of a vast fossil forest that — 318 million years ago — would have been situated at the equator. Among the fossilized tree stumps and trunks, many of which are preserved in upright positions, is one of the richest fossil records of early tetrapods.</p>
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<strong>
Read more:
<a href="https://theconversation.com/310-million-year-old-tree-fossils-to-reveal-new-ancient-animals-120195">310 million-year-old tree fossils to reveal new ancient animals</a>
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<p>The significance of these expansive fossil beds was recognized centuries ago by some of the leading geologists and paleontologists of the 19th century, when Darwin’s theory of evolution was revolutionizing the field of biology. It was at the Joggins Fossil Cliffs that geologist Charles Lyell developed <a href="https://doi.org/10.4138/2155">his foundational theory regarding the formation of coal</a> and where Lyell and <a href="http://www.biographi.ca/en/bio/dawson_john_william_12E.html">geologist Sir John William Dawson</a> discovered what were, at the time, the earliest known fossils of land animals. </p>
<p>These animal fossils have since been periodically revisited, first by <a href="http://doi.org/10.1111/j.1096-3642.1938.tb00027.x">Irish paleontologist Margaret Steen in the 1920s</a> and later by <a href="https://montrealgazette.remembering.ca/obituary/robert-lynn-carroll-1079012578">Canadian paleontologist Bob L. Carroll</a>, the father of Canadian vertebrate paleontology and longtime professor at McGill University. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/334530/original/file-20200512-82361-1y9kyt6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/334530/original/file-20200512-82361-1y9kyt6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/334530/original/file-20200512-82361-1y9kyt6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=322&fit=crop&dpr=1 600w, https://images.theconversation.com/files/334530/original/file-20200512-82361-1y9kyt6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=322&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/334530/original/file-20200512-82361-1y9kyt6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=322&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/334530/original/file-20200512-82361-1y9kyt6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=404&fit=crop&dpr=1 754w, https://images.theconversation.com/files/334530/original/file-20200512-82361-1y9kyt6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=404&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/334530/original/file-20200512-82361-1y9kyt6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=404&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Photograph of an excavation team led by Hillary Maddin and Arjan Mann at the Joggins Fossil Cliffs.</span>
<span class="attribution"><span class="source">(Hillary Maddin)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>The mystery of mammalian origins</h2>
<p>The earliest ancestors of mammals appeared more than 300 million years ago. However, just like the ancestors of other groups of living animals, like amphibians and birds, early synapsids looked nothing like modern mammals. In particular, distinguishing early synapsids from early reptiles can be a real challenge. </p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/334203/original/file-20200512-66707-rb4a12.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/334203/original/file-20200512-66707-rb4a12.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/334203/original/file-20200512-66707-rb4a12.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=1091&fit=crop&dpr=1 600w, https://images.theconversation.com/files/334203/original/file-20200512-66707-rb4a12.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=1091&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/334203/original/file-20200512-66707-rb4a12.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=1091&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/334203/original/file-20200512-66707-rb4a12.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1371&fit=crop&dpr=1 754w, https://images.theconversation.com/files/334203/original/file-20200512-66707-rb4a12.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1371&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/334203/original/file-20200512-66707-rb4a12.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1371&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Photograph (A) and interpretive illustration (B) of the new Joggins synapsid, <em>Asaphestera playtris</em>.</span>
<span class="attribution"><span class="source">(Arjan Mann)</span></span>
</figcaption>
</figure>
<p>Although we thought we were studying only one animal, <em>Asaphestera intermedia</em>, one of our major findings was recognizing that what previous paleontologists had thought was a single animal was actually a composite of multiple fossils of at least three very different animals! We could only be certain of two of them: a new reptile we named <em>Steenerpeton silvae</em> and an early synapsid, <em>Asaphestera platyris</em>, with evidence of a single temporal opening in the skull. </p>
<p>The original convolution of these species highlights how subtle the differences were between early mammal ancestors and early reptiles, and the value of re-evaluating historic fossil collections to appraise their identity in light of more recent work. <em>Asaphestera platyris</em> provides the oldest evidence of mammal-like reptiles in the fossil record, establishing a firm date for their diversification around 315 million years ago.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/334200/original/file-20200512-66719-1tdhebg.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/334200/original/file-20200512-66719-1tdhebg.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/334200/original/file-20200512-66719-1tdhebg.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=413&fit=crop&dpr=1 600w, https://images.theconversation.com/files/334200/original/file-20200512-66719-1tdhebg.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=413&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/334200/original/file-20200512-66719-1tdhebg.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=413&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/334200/original/file-20200512-66719-1tdhebg.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=519&fit=crop&dpr=1 754w, https://images.theconversation.com/files/334200/original/file-20200512-66719-1tdhebg.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=519&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/334200/original/file-20200512-66719-1tdhebg.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=519&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Photograph (A) and interpretive drawing of the new Joggins reptile, <em>Steenerpeton silvae</em>. Letter abbreviations refer to different anatomical elements.</span>
<span class="attribution"><span class="source">(Arjan Mann)</span></span>
</figcaption>
</figure>
<h2>Climate change and rainforest collapse</h2>
<p>The fossil cliffs at Joggins preserve a time right before a period of drastic climate change. The period between 370 to 300 million years ago was a cold period in Earth’s history, <a href="https://doi.org/10.1130/0091-7613(2003)031%3C0605:GCDCGO%3E2.0.CO;2">with extensive ice sheets covering much of the Southern Hemisphere</a>. Around 307 million years ago, the Earth began a process of global warming. This culminated in the largest mass extinction in Earth’s history approximately 50 million years later. </p>
<p>At the time, much of the equatorial region was covered in rainforests and tropical swamps, which were later fossilized as extensive coal layers across North America and Europe. When the warming began, these habitats dried up in an event called the <a href="http://dx.doi.org/10.5061/dryad.n4k45">Carboniferous rainforest collapse</a>, which triggered a minor mass extinction in these biodiversity hot spots. </p>
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Read more:
<a href="https://theconversation.com/rainforest-collapse-in-prehistoric-times-changed-the-course-of-evolution-91289">Rainforest collapse in prehistoric times changed the course of evolution</a>
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<p>The survivors were all <a href="https://doi.org/10.1038/s41559-018-0776-z">early representatives of modern animal groups</a>, such as modern amphibians and modern reptiles, and showed adaptations for surviving in drier environments.</p>
<p>Joggins is unique in preserving an early glimpse of some of these modern groups before the Carboniferous rainforest collapse. What we find are animals that survived the rainforest collapse were living alongside many of the animals that went extinct, but were rarer, smaller and harder to identify, like <em>Asaphestera</em>. This flies in the face of <a href="https://doi.org/10.1093/icb/15.2.371">some ideas about the origin of these later groups</a>, which suggest that these more advanced animals originated at higher elevations or outside the tropics.</p>
<p>We still have a way to go to fully understand these earliest members of our own lineage, but these important fossils from Nova Scotia are pointing the way.</p><img src="https://counter.theconversation.com/content/138103/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Arjan Mann receives funding from Ontario graduate scholarship.</span></em></p><p class="fine-print"><em><span>Bryan Gee and Jason D. Pardo 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>A very early mammal ancestor is one of the most recent discoveries at the Joggins Fossil Cliffs in Nova Scotia. This new finding sheds further light on theories of mammalian evolution.Arjan Mann, Ph.D. Candidate, Palaeontology, Carleton UniversityBryan Gee, Ph.D. candidate, Ecology & Evolutionary Biology, University of TorontoJason D. Pardo, PhD Candidate, Evolutionary Biology, University of CalgaryLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1290722020-03-18T18:49:43Z2020-03-18T18:49:43ZWhen fish gave us the finger: this ancient four-limbed fish reveals the origins of the human hand<figure><img src="https://images.theconversation.com/files/314679/original/file-20200211-146696-plfpfl.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C5668%2C2809&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Katrina Kenny</span>, <span class="license">Author provided</span></span></figcaption></figure><p>One of the most significant events in the history of life was when fish evolved into <a href="https://ucmp.berkeley.edu/vertebrates/tetrapods/tetraintro.html">tetrapods</a>, crawling out of the water and eventually conquering land. The term tetrapod refers to four-limbed <a href="https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Book%3A_General_Biology_(Boundless)/29%3A_Vertebrates/29.1%3A_Chordates/29.1D%3A_Characteristics_of_Vertebrates">vertebrates</a>, including humans.</p>
<p>To complete this transition, several anatomical changes were necessary. One of the most important was the evolution of hands and feet. </p>
<p>Working with researchers from the University of Quebec, in 2010 we discovered the first complete specimen of <em>Elpistostege watsoni</em>. This tetrapod-like fish lived more than 380-million-years ago, and belonged to a group called <a href="https://www.miguasha.ca/mig-en/elpistostegalians.php">elpistostegalians</a>. </p>
<p>Our research based on this specimen, published today in <a href="https://www.nature.com/articles/s41586-020-2100-8">Nature</a>, suggests human hands likely evolved from the fins of this fish, which we’ll refer to by its genus name, <em>Elpistostege</em>.</p>
<p>Elpistostegalians are an extinct group that displayed features of both lobe-finned fish and early tetrapods. They were likely involved in bridging the gap between prehistoric fish and animals capable of living on land. </p>
<p>Thus, our latest finding offers valuable insight into the evolution of the vertebrate hand.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/316990/original/file-20200225-24664-2uvtzp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/316990/original/file-20200225-24664-2uvtzp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/316990/original/file-20200225-24664-2uvtzp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=439&fit=crop&dpr=1 600w, https://images.theconversation.com/files/316990/original/file-20200225-24664-2uvtzp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=439&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/316990/original/file-20200225-24664-2uvtzp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=439&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/316990/original/file-20200225-24664-2uvtzp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=552&fit=crop&dpr=1 754w, https://images.theconversation.com/files/316990/original/file-20200225-24664-2uvtzp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=552&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/316990/original/file-20200225-24664-2uvtzp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=552&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>Elpistostege</em>, from the Late Devonian period of Canada, is now considered the closest fish to tetrapods (four-limbed land animals), which includes humans.</span>
<span class="attribution"><span class="source">Brian Choo</span></span>
</figcaption>
</figure>
<h2>The best specimen we’ve ever found</h2>
<p>To understand how fish fins became limbs (arms and legs with digits) through evolution, we studied the fossils of extinct lobe-finned fishes and early tetrapods. </p>
<p>Lobe-fins include bony fishes (Osteichthyes) with robust fins, such as <a href="https://ucmp.berkeley.edu/vertebrates/sarco/dipnoi.html">lungfishes</a> and <a href="https://www.nationalgeographic.com/animals/fish/group/coelacanths/">coelacanths</a>.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/ancient-fish-evolved-in-shallow-seas-the-very-places-humans-threaten-today-105386">Ancient fish evolved in shallow seas – the very places humans threaten today</a>
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<p>Elpistostegalians lived between 393–359 million years ago, during the Middle and Upper <a href="https://www.nationalgeographic.com/science/prehistoric-world/devonian/">Devonian times</a>. Our finding of a complete 1.57m <em>Elpistostege</em> – uncovered from <a href="https://whc.unesco.org/en/list/686/">Miguasha National Park</a> in Quebec, Canada – is the first instance of a complete skeleton of any elpistostegalian fish fossil. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/uyUYKTBA91k?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">This animation shows what <em>Elpistostege</em> might have looked like when alive, and highlights the close similarities in its pectoral fin skeleton to the bones of our human arm and hand.</span></figcaption>
</figure>
<p>Prior to this, the most complete elpistostegalian specimen was a <a href="https://evolution.berkeley.edu/evolibrary/news/060501_tiktaalik"><em>Tiktaalik roseae</em> skeleton</a> found in the Canadian Arctic in 2004, but it was missing the extreme-end part of its fin.</p>
<h2>When fins became limbs</h2>
<p>The origin of digits in land vertebrates is hotly debated. </p>
<p>The tiny bones in the tip of the pectoral fins of fishes such as <em>Elpistostege</em> are called “radial” bones. When radials form a series of rows, like digits, they are essentially the same as fingers in tetrapods. </p>
<p>The only difference is that, in these advanced fishes, the digits are still locked within the fin, and not yet free moving like human fingers.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-how-do-fish-sleep-126018">Curious Kids: how do fish sleep?</a>
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</em>
</p>
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<p>Our recently uncovered <em>Elpistostege</em> specimen reveals the presence of a humerus (arm), radius and ulna (forearm), rows of carpal bones (wrist) and smaller bones organised in discrete rows. </p>
<p>We believe this is the first evidence of digit bones found in a fish fin with fin-rays (the bony rays that support the fin). This suggests the fingers of vertebrates, including of human hands, first evolved as rows of digit bones in the fins of <em>Elpistostegalian</em> fishes.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/315892/original/file-20200218-11044-vtrp8s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/315892/original/file-20200218-11044-vtrp8s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/315892/original/file-20200218-11044-vtrp8s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=350&fit=crop&dpr=1 600w, https://images.theconversation.com/files/315892/original/file-20200218-11044-vtrp8s.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=350&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/315892/original/file-20200218-11044-vtrp8s.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=350&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/315892/original/file-20200218-11044-vtrp8s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=440&fit=crop&dpr=1 754w, https://images.theconversation.com/files/315892/original/file-20200218-11044-vtrp8s.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=440&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/315892/original/file-20200218-11044-vtrp8s.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=440&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 pectoral fin of <em>Elpistostege</em> shows the short rows of aligned digits in the fin - an intermediate stage between fishes and land animals such as the early tetrapod Tulerpeton.</span>
<span class="attribution"><span class="source">Author provided</span></span>
</figcaption>
</figure>
<h2>What’s the evolutionary advantage?</h2>
<p>From an evolutionary perspective, rows of digit bones in prehistoric fish fins would have provided flexibility for the fin to more effectively bear weight. </p>
<p>This could have been useful when <em>Elpistostege</em> was either plodding along in the shallows, or trying to move out of water onto land. Eventually, the increased use of such fins would have lead to the loss of fin-rays and the emergence of digits in rows, forming a larger surface area for the limb to grip the land surface.</p>
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<strong>
Read more:
<a href="https://theconversation.com/walking-fish-help-scientists-to-understand-how-we-left-the-ocean-91411">'Walking' fish help scientists to understand how we left the ocean</a>
</strong>
</em>
</p>
<hr>
<p>Our specimen shows many features not known before, and will form the basis of a series of future papers describing in detail its skull, and other aspects of its body skeleton.</p>
<p><em>Elpistostege</em> blurs the line between fish and vertebrates capable of living on land. It’s not necessarily our ancestor, but it’s now the closest example we have of a “transitional fossil”, closing the gap between fish and tetrapods. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/321178/original/file-20200317-60889-61d2vh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/321178/original/file-20200317-60889-61d2vh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/321178/original/file-20200317-60889-61d2vh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=276&fit=crop&dpr=1 600w, https://images.theconversation.com/files/321178/original/file-20200317-60889-61d2vh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=276&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/321178/original/file-20200317-60889-61d2vh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=276&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/321178/original/file-20200317-60889-61d2vh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=346&fit=crop&dpr=1 754w, https://images.theconversation.com/files/321178/original/file-20200317-60889-61d2vh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=346&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/321178/original/file-20200317-60889-61d2vh.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">Our new specimen of <em>Elpistostege watsoni</em> measures 1.57 metres long from its snout to the tip of its tail.</span>
<span class="attribution"><span class="source">Richard Cloutier, UQAR</span></span>
</figcaption>
</figure>
<h2>The full picture</h2>
<p>The first <em>Elpistostege</em> fossil, a skull fragment, was found in the late 1930s. It was thought to belong to an early amphibian. In the mid 1980s the front half of the skull was found, and was confirmed to be an advanced lobe-finned fish.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/313663/original/file-20200205-149742-rmskys.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/313663/original/file-20200205-149742-rmskys.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/313663/original/file-20200205-149742-rmskys.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=290&fit=crop&dpr=1 600w, https://images.theconversation.com/files/313663/original/file-20200205-149742-rmskys.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=290&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/313663/original/file-20200205-149742-rmskys.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=290&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/313663/original/file-20200205-149742-rmskys.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=365&fit=crop&dpr=1 754w, https://images.theconversation.com/files/313663/original/file-20200205-149742-rmskys.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=365&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/313663/original/file-20200205-149742-rmskys.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=365&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 original finds of the <em>Elpistostege</em> skull roof (left) and front half of the skull. The new specimen confirms these all belong to the one species.</span>
<span class="attribution"><span class="source">Richard Cloutier/UQAR</span></span>
</figcaption>
</figure>
<p>Our new, complete specimen was discovered in the fossil-rich cliffs of the <a href="https://whc.unesco.org/en/list/686/">Miguasha National Park</a>, a UNESCO World Heritage site in Eastern Canada. Miguasha is considered one of the best sites to study fish fossils from the Devonian period (known as the “Age of Fish”), as it contains a very large number of lobe-finned fish fossils, in an exceptional state of preservation.</p><img src="https://counter.theconversation.com/content/129072/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>John Long receives funding from The Australian Research Council</span></em></p><p class="fine-print"><em><span>Richard Cloutier receives funding from Natural Science and Engineering Research Council of Canada and The Australian Research Council. </span></em></p>The arrangement of bones in our specimen’s fins are the same as those of ‘fingers’ in tetrapods. The only difference is the digits are locked within the fin, and not free moving.John Long, Strategic Professor in Palaeontology, Flinders UniversityRichard Cloutier, Professor of Evolutionary Biology, Université du Québec à Rimouski, Université du Québec à Rimouski (UQAR)Licensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1151472019-04-17T19:48:18Z2019-04-17T19:48:18ZWe scanned one of our closest cousins, the coelacanth, to learn how its brain grows<p>There’s a lot that’s fascinating about the coelacanth <em>Latimeria</em>. Now under threat, this deep-sea fish is closely related to humans and other back-boned, land dwelling animals (tetrapods). </p>
<p>The coelacanth <em>Latimeria</em> is a relatively large fish (reaching about 2 metres long) but has a very tiny brain lying within a hinged braincase – a very primitive feature found in many fossil fishes. </p>
<p>How the coelacanth skull grows and why the brain remains so small has puzzled scientists for years. Our new study <a href="https://www.nature.com/articles/s41586-019-1117-3">published today</a> in Nature illuminates for the first time the development of the brain and skull of this curious animal. </p>
<p>It’s another piece of evidence that might help us see where humans once came from. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/its-less-than-2cm-long-but-this-400-million-year-old-fossil-fish-changes-our-view-of-vertebrate-evolution-96419">It's less than 2cm long, but this 400 million year old fossil fish changes our view of vertebrate evolution</a>
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</p>
<hr>
<h2>Discovery of a living coelacanth</h2>
<p>The <a href="https://www.nature.com/articles/143455a0">discovery of a living <em>Latimeria</em> coelacanth</a> rocked the world in 1939, as scientists thought they had died out with the dinosaurs about 66 million years ago. </p>
<p>The first <em>Latimeria</em> ever found was accidentally caught in a trawl off the South African coast. Amazingly, its overall body shape was strikingly similar to some of its fossilised relatives that had been known by palaeontologists since the 19th century.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/269289/original/file-20190415-147502-pkouuq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/269289/original/file-20190415-147502-pkouuq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/269289/original/file-20190415-147502-pkouuq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=199&fit=crop&dpr=1 600w, https://images.theconversation.com/files/269289/original/file-20190415-147502-pkouuq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=199&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/269289/original/file-20190415-147502-pkouuq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=199&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/269289/original/file-20190415-147502-pkouuq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=250&fit=crop&dpr=1 754w, https://images.theconversation.com/files/269289/original/file-20190415-147502-pkouuq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=250&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/269289/original/file-20190415-147502-pkouuq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=250&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 fossil coelacanth Trachymetopon from the Jurassic of Germany. This specimen is housed in the collections of the Museum der Universität Tübingen.</span>
<span class="attribution"><span class="source">Hugo Dutel (no commercial use)</span></span>
</figcaption>
</figure>
<p>The scientific frenzy around <em>Latimeria</em> was really sparked by what the animal could reveal about the origin of humans and other four-limbed animals. </p>
<p>At the time of its discovery, <em>Latimeria</em> held a pivotal position in the family tree of vertebrates (animals with backbones). It was considered the direct descendant of lobe-finned fishes, the group of fish from which tetrapods evolved. </p>
<p>So the discovery of a living <em>Latimeria</em> coelacanth was expected to shed light into the biology of our very early ancestors.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/ancient-fish-evolved-in-shallow-seas-the-very-places-humans-threaten-today-105386">Ancient fish evolved in shallow seas – the very places humans threaten today</a>
</strong>
</em>
</p>
<hr>
<h2>Our fishy family tree</h2>
<p>Nowadays, expectations have been tempered. The development of new methods for reconstructing the evolution of organisms, the discovery of new fossils, and, more recently, information extracted from DNA and other molecules have slightly changed this picture. </p>
<p>Among living vertebrates, coelacanths are <a href="https://www.nature.com/articles/nature12027">no longer regarded as the closest relatives to tetrapods</a> – they have been replaced by another old group of fishes, the <a href="https://www.britannica.com/animal/lungfish">lungfishes</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/269278/original/file-20190415-147511-w3txq5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/269278/original/file-20190415-147511-w3txq5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/269278/original/file-20190415-147511-w3txq5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=316&fit=crop&dpr=1 600w, https://images.theconversation.com/files/269278/original/file-20190415-147511-w3txq5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=316&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/269278/original/file-20190415-147511-w3txq5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=316&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/269278/original/file-20190415-147511-w3txq5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=397&fit=crop&dpr=1 754w, https://images.theconversation.com/files/269278/original/file-20190415-147511-w3txq5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=397&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/269278/original/file-20190415-147511-w3txq5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=397&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Simplified phylogeny of the bony fishes (osteichthyans). Coelacanths and lungfishes are the only living lobe-finned fishes and are closely related to tetrapods, the land-dwelling vertebrates. The intracranial joint is a primitive feature of sarcopterygians, the group that includes lobe-finned fishes and tetrapods. It is found in many fossil lobe-finned fishes from the Devonian, but has been independently lost in tetrapods and living lungfishes. The coelacanth is the only living vertebrate which possesses an intracranial joint.</span>
<span class="attribution"><span class="source">Hugo Dutel (no commercial reuse)</span></span>
</figcaption>
</figure>
<p>Yet, the <em>Latimeria</em> coelacanth possesses some unusual features that are still of interest for understanding the evolution of our fossil relatives.</p>
<p>The skull of <em>Latimeria</em> is completely split in half by a joint called the “intracranial joint”. This joint is a very primitive feature that is otherwise found only in many extinct lobe-finned fishes. </p>
<p>In contrast with other vertebrates, the brain of <em>Latimeria</em> is ridiculously small compared with the cavity that houses it (1% of the entire braincase volume).</p>
<p>The rear of the skull of <em>Latimeria</em> and extinct lobe-finned fishes also straddles a surprisingly huge structure called the <a href="https://www.britannica.com/science/notochord">notochord</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/269285/original/file-20190415-147487-3kwee.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/269285/original/file-20190415-147487-3kwee.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/269285/original/file-20190415-147487-3kwee.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=256&fit=crop&dpr=1 600w, https://images.theconversation.com/files/269285/original/file-20190415-147487-3kwee.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=256&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/269285/original/file-20190415-147487-3kwee.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=256&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/269285/original/file-20190415-147487-3kwee.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=322&fit=crop&dpr=1 754w, https://images.theconversation.com/files/269285/original/file-20190415-147487-3kwee.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=322&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/269285/original/file-20190415-147487-3kwee.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=322&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">3D virtual reconstruction of the coelacanth skull in right lateral view. Left: Overall view of the skull. Right: the braincase isolated and virtually cut open along the midline to show the brain (yellow) and the notochord (green). The brain represents about 1% of the volume of the cavity which houses it.</span>
<span class="attribution"><span class="source">Hugo Dutel</span></span>
</figcaption>
</figure>
<p>The question of how this skull and brain develops, and what it means to vertebrate evolution, triggered our work published today.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/what-evolution-and-motorcycles-have-in-common-lets-take-a-ride-across-australia-95880">What evolution and motorcycles have in common: let's take a ride across Australia</a>
</strong>
</em>
</p>
<hr>
<h2>Finding unborn Coelacanths</h2>
<p><em>Latimeria</em> is ovoviviparous, meaning that eggs develop in the female abdomen, and then she gives birth to live young. </p>
<p>But studying the development of this fish is not an easy thing. <em>Latimeria</em> cannot be bred in an aquarium, so embryos and fetuses cannot be easily obtained. Moreover, we cannot capture any coelacanths in the wild as they are protected. </p>
<p>Many adult coelacanths are held in natural history collections. However, earlier life stages are extremely scarce as they came from the rare captures of pregnant females. For a long time, scientists thus could not dissect these precious specimens to study their anatomy. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/269553/original/file-20190416-147522-td1m5y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/269553/original/file-20190416-147522-td1m5y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/269553/original/file-20190416-147522-td1m5y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=200&fit=crop&dpr=1 600w, https://images.theconversation.com/files/269553/original/file-20190416-147522-td1m5y.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=200&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/269553/original/file-20190416-147522-td1m5y.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=200&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/269553/original/file-20190416-147522-td1m5y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=251&fit=crop&dpr=1 754w, https://images.theconversation.com/files/269553/original/file-20190416-147522-td1m5y.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=251&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/269553/original/file-20190416-147522-td1m5y.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=251&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 growth series of Latimeria collected for our study.</span>
<span class="attribution"><span class="source">Hugo Dutel</span></span>
</figcaption>
</figure>
<p>So we used state-of-the-art X-ray scanning facilities at the <a href="http://www.esrf.eu/">European synchrotron</a> and <a href="https://icm-institute.org/fr/cenir-human-mri-nueroimaging-core-facility-for-clinical-research/">powerful MRI</a> to visualise the internal anatomy of these precious museum specimens. </p>
<p>Thanks to these data, we generated digital 3D models of the skull at each stage of its growth. The detailed 3D models allowed us to describe how the form of the skull, the brain and the notochord changes from a very early fetus to an adult. </p>
<h2>How the brain grows but stays tiny</h2>
<p>We found that the relative size of the brain dramatically decreases during development. The brain grows, but not as much as the surrounding structures in the head. </p>
<p>This is is very unusual, and not seen in other vertebrates (and especially us primates, in which the brain expands dramatically during growth). </p>
<p>On the other hand, the notochord expands considerably to become much bigger than the brain in the adult. This is very unique, as the notochord usually degenerates in the early development of most vertebrates. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/269299/original/file-20190415-147508-gpy5ej.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/269299/original/file-20190415-147508-gpy5ej.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/269299/original/file-20190415-147508-gpy5ej.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=120&fit=crop&dpr=1 600w, https://images.theconversation.com/files/269299/original/file-20190415-147508-gpy5ej.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=120&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/269299/original/file-20190415-147508-gpy5ej.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=120&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/269299/original/file-20190415-147508-gpy5ej.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=151&fit=crop&dpr=1 754w, https://images.theconversation.com/files/269299/original/file-20190415-147508-gpy5ej.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=151&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/269299/original/file-20190415-147508-gpy5ej.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=151&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 brain (yellow) within the braincase (blue) at different developmental stages of Latimeria.</span>
<span class="attribution"><span class="source">Hugo Dutel</span></span>
</figcaption>
</figure>
<p>Why is the brain of <em>Latimeria</em> so small? </p>
<p>As is often the case, there is probably not a single explanation. It might be due to the way the notochord develops, and the position and function of the intracranial joint (which is probably plays a role in biting). It is also possible that the energy needed by a huge electrosensory organ in <em>Latimeria</em>‘s snout, <a href="https://www.nature.com/articles/srep08962">the rostral organ</a>, may come at the expense of having a bigger brain. </p>
<p>Together with a recent <a href="https://www.nature.com/articles/ncomms9222">study on its lung</a> (which has bony plates on it), these findings represent the best of our knowledge on the development of <em>Latimeria</em>. It remains one of our most mysterious cousins, as many aspects of its biology and ecology remain unknown. </p>
<p>For sure, <em>Latimeria</em> still holds many promising clues for our understanding of vertebrate evolution and our distant origins. </p>
<p>But this only survivor of a <a href="https://royalsocietypublishing.org/doi/full/10.1098/rsbl.2006.0470">400 million year old group</a> and its marine ecosystem are in jeopardy and need to be protected more than ever.</p><img src="https://counter.theconversation.com/content/115147/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Hugo Dutel receives funding from the Natural Environment Research Council (NE/P013090/1). </span></em></p><p class="fine-print"><em><span>John Long receives funding from The Australian Research Council</span></em></p>The discovery of a living coelacanth fish rocked the world in 1939, as scientists thought they had died out with the dinosaurs. A new study illuminates how its skull and tiny brain develop.Hugo Dutel, Research associate, University of BristolJohn Long, Strategic Professor in Palaeontology, Flinders UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1118552019-02-18T16:29:32Z2019-02-18T16:29:32ZLand animal diversity was stable for millions of years, before humans came along – new study<figure><img src="https://images.theconversation.com/files/259064/original/file-20190214-1751-o6s4q8.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Mark Ryan/Mary Parrish/Jay Matternes/Smithsonian Institution</span></span></figcaption></figure><p>Species living on land make up 85% to 95% of all biodiversity <a href="https://academic.oup.com/icb/article/50/4/675/650584">on Earth today</a>. This is especially impressive when we consider that the continents cover only 30% of our planet’s surface area. And that most land species are descendants of a small number of pioneering groups that invaded the land about 400m years ago.</p>
<p>Surprisingly, though, scientists strongly disagree about when land biodiversity reached modern levels. Is what we see today <a href="https://www.journals.uchicago.edu/doi/10.1086/680850">typical</a> of the last several tens, or even hundreds, of millions of years? Or has diversity been increasing exponentially, with <a href="http://max2.ese.u-psud.fr/epc/conservation/PDFs/HIPE/Harmon2015.pdf">substantially more</a> species alive today than ever before? </p>
<p>In a <a href="https://www.nature.com/articles/s41559-019-0811-8.epdf?author_access_token=w2i-KLbF8FbzCAZyy6WGp9RgN0jAjWel9jnR3ZoTv0MiKUtR7u1rX-v60IL0d3bJT3W4nAFyq5XiVc0eP-BiQRazBNDFX76GS8dr3ahixWpIxMrSjAwvJM3NQMB3L8_EAmcf9iPpI2mNr3rNVgTeLw%3D%3D">new paper</a> in Nature Ecology & Evolution, my co-authors and I examined how the diversity of land vertebrate species living in “local” ecosystems (also known “ecological communities”) changed over the last 375m years. We analysed nearly 30,000 fossil sites that have produced fossils of tetrapods, land vertebrate animals, such as mammals, birds, reptiles (including dinosaurs) and amphibians. Counting species within individual fossil sites allowed us to estimate the diversity in ancient ecological communities. </p>
<p>Our results show that the rich levels of biodiversity on land seen across the globe today are not a recent phenomenon. Diversity within tetrapod ecosystems has been similar for at least the last 60m years, since soon after the extinction of the dinosaurs. This suggests that the prominent idea that biodiversity within ecosystems rises more or less <a href="http://max2.ese.u-psud.fr/epc/conservation/PDFs/HIPE/Harmon2015.pdf">continuously over time</a> is incorrect. Instead, it’s likely that the way species interact – for example, by competing for resources such as space and food – tends to limit the number of species that can be packed into local ecosystems.</p>
<p>That doesn’t mean that local diversity in tetrapods hasn’t increased over the course of the last 375m years. Our results also show that this diversity is at least three times higher today than it was around 300m years ago, when tetrapods first evolved key innovations for life on land (such as the <a href="https://ucmp.berkeley.edu/vertebrates/tetrapods/amniota.html">amniotic egg</a>, which allowed reproduction away from water sources). However, we discovered that increases in diversity are rare and happen relatively abruptly in geological terms. They are also usually followed by tens of millions of years when no increases occur.</p>
<p>Counterintuitively, the largest increase in local diversity took place after the mass extinction that wiped out the dinosaurs, 66m years ago. Within only a few million years of this event, local diversity had increased by two to three times over pre-extinction levels, largely thanks to the spectacular success of modern mammals, which evolved to fill the ecological space left by the dinosaurs. But after this large rise, local tetrapod diversity didn’t increase over the next 60m years. </p>
<h2>Different scales</h2>
<p>The competing models of animal diversification make clear predictions about how diversity at the local scale should change over geological time, with either long-term stability or continual increases. By demonstrating that there are limits to local diversity that persist for millions of years, our results pose a challenge to models that show diversification continues more or less unchecked. But diversity at the continental or global level could follow a separate pattern, so our results don’t necessarily apply at these scales as well. </p>
<p>For example, following a mass extinction, most species on a continent could be wiped out. But a relatively small number of surviving species could become very successful and spread widely. In this scenario, diversity over the whole continent would crash, but local diversity could appear to be unchanged because the same small set of species would be found everywhere.</p>
<p>In fact, a similar process appears to be <a href="https://pdxscholar.library.pdx.edu/cgi/viewcontent.cgi?article=1068&context=polisci_fac">happening now</a> in response to habitat destruction caused by humans. Invasive species are spreading widely, sometimes pushing up local diversity even while regional diversity may be falling. But <a href="https://research.birmingham.ac.uk/portal/files/41243162/Close_et_al_Controlling_species_area_effect_Nature_Communications.pdf">previous work</a> by my research group on continental-scale land vertebrate diversity in the Mesozoic and early Cenozoic eras (around 250m to 47m years ago) suggests that, over long timescales, species counts within continents show a similar pattern to those at the local scale. This means that the spectacular diversity on land today – at least within vertebrates – is probably not a recent innovation.</p><img src="https://counter.theconversation.com/content/111855/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Roger Close receives funding from the European Research Council (ERC). </span></em></p>Local tetrapod biodiversity exploded after the dinosaurs, but has barely changed in 60m years.Roger Close, ERC Research Fellow in Palaeobiology, University of BirminghamLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/977472018-06-08T09:57:35Z2018-06-08T09:57:35ZFossil find offers first evidence of four-legged aquatic ancestors in Africa<figure><img src="https://images.theconversation.com/files/221567/original/file-20180604-175407-fa8pxv.jpg?ixlib=rb-1.1.0&rect=243%2C0%2C3810%2C3458&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An artist's impression of Tutusius at Waterloo Farm.</span> <span class="attribution"><span class="source">Illustration by Maggie Newman</span></span></figcaption></figure><p>Some of our ancestors had four legs, a finned tail and lived in water. They were aquatic <a href="https://evolution.berkeley.edu/evolibrary/article/evograms_04">tetrapods</a> which, after the end of the Devonian period 359 million years ago, increasingly moved onto the land. These land dwellers were the ancestors of all amphibians, reptiles, birds and mammals.</p>
<p>Fossil records have always suggested that those aquatic Devonian tetrapods never lived on what is today the African continent. At the time, prior to the collision of Gondwana and the northern continent of Laurussia around 320 million years ago, Africa was part of the supercontinent <a href="https://www.livescience.com/37285-gondwana.html">called Gondwana</a>. Gondwana also comprised of modern South America, Australia, Antarctica, India and Madagascar. </p>
<p>The only records of Devonian tetrapods from Gondwana were a jaw and some footprints from eastern Australia which at the time formed part of the tropical northern coast of Gondwana. </p>
<p>Almost all of the sparse records of Devonian tetrapods came from the tropical regions of Laurussia. It was made up of what are now North America, Greenland and Europe. This led to a commonly held scientific assumption that all Devonian tetrapods lived in tropical environments and that they probably originated in Laurussia. </p>
<p>But <a href="http://science.sciencemag.org/content/360/6393/1120.full">a discovery I made</a> at a fossil site in South Africa’s Eastern Cape province turns this view on its head. During the Devonian period what is now Africa lay over the South Pole; the Eastern Cape was well within the Antarctic Circle. My discovery of two separate fossils tetrapod species proves that tetrapods lived all over the world by the end of Devonian. </p>
<p>It implies that tetrapods could have originated anywhere and that the next step, the move out of water and onto land could also have occurred anywhere. Tetrapods could have as easily evolved in what is now Africa as in what is now Europe or Greenland. </p>
<p>The fossil species belonging to two previously unknown genera, which I’ve named <em>Tutusius</em> and <em>Umzantsia</em>, are significant to our understanding of evolution. It means that tetrapods weren’t specifically tropical, and so their “step” from water to land wasn’t necessarily uniquely tied to the conditions in tropical environments. They may equally well have evolved under very different conditions nearer the poles.</p>
<p>This find will encourage people to look all over the world for clues to this key macroevolutionary transition, rather than just reinforcing the previous assumptions about where they lived by only looking for clues in tropically deposited rocks.</p>
<p>It also means that we can hope to find more clues to this important stage of our development here in Africa – which wasn’t at all expected before.</p>
<h2>Uncovering new species</h2>
<p>For the past 20 years, I’ve been carefully flaking through blocks of rock rescued from a fossil site called Waterloo Farm near Grahamstown in South Africa. I worked on the site in the mid 1990s and was intent on continuing research there. However, roadworks in the area in 1999 and again in 2007 threatened this unique piece of ancient heritage. </p>
<p>The black shale from Waterloo Farm was deposited as fine, organic-rich oxygen-depleted gooey mud at the bottom of a brackish estuarine lake, seasonally linked to the sea. It is the only known site from the latest Devonian in all of Africa that preserved the remains of bony animals, including about 20 species of fish that were previously unknown to science. </p>
<p>Some of these exhibit rare preservation of their soft tissues, such as <em><a href="https://www.nature.com/articles/nature05150">Priscomyzon</a></em>, the exquisitely preserved remains of the world’s oldest fossil lamprey. </p>
<p>The special type of preservation has also preserved an unparalleled record of algae and waterweeds, bivalves and eurypterids that shared the lake with the bony denizens. The woodland that lined the landward side of the lake is also represented by the remains of dozens of species of plants. <a href="http://www.sci-news.com/paleontology/science-scorpion-fossil-01350.html">Scorpion fragments</a> that were washed into the estuary provide the earliest record of land living animals from Gondwana.</p>
<p>All of this was almost lost. But when I approached the South African National Roads Agency Limited, which is responsible for road management, they agreed to help me rescue tens of tons of hand mined shale blocks for systematic ongoing excavation so they could be thoroughly checked for fossil remnants.</p>
<p>These are stored in custom made sheds to protect them from the weather and excavation is ongoing. I have already collected thousands of fossils which have become part of the <a href="http://www.am.org.za/">Albany Museum’s</a> collection in Grahamstown. </p>
<p>It was while flaking through a block of the Waterloo shale I uncovered the cleithrum of the species I’ve named <em>Tutusius</em>. This is one of the main bones that form part of the shoulder girdle of fishes and early tetrapods. As a result of the radical change in structure and movement during the fin to limb transition its structure in early tetrapods is very distinctive.</p>
<p>I immediately recognised it as being from a Devonian tetrapod, which was confirmed by tetrapod experts Professor Michael Coates of the University of Chicago and Professor Per Ahlberg of Uppsala University in Sweden. At this point I started discussing a possible collaboration with Professor Ahlberg.</p>
<p>Then in early 2017 I discovered a second but different tetrapod cleithrum, this one hidden among fish scales on a slab I collected nearly 20 years ago at Waterloo Farm.</p>
<p>This bone belonged to the genus I’ve named <em>Umzantsia</em>. I emailed Professor Ahlberg a picture of it. He was equally excited and we made arrangements for him to join me in South Africa to write up the discoveries together.</p>
<p>In September 2017 we carefully combed through the Waterloo Farm collection and identified a number of other bones from <em>Umzantsia</em>. We’ve examined these and found many characteristics to confirm that the bones belong to a stem tetrapod species.</p>
<p>The next step – in between my lecturing duties and writing up of scientific papers – will be to conduct further excavations at the Waterloo Farm sheds. I feel confident that these will unearth exciting new tetrapod remains. It’s also possible, though substantially less certain, that we may find Devonian tetrapod remains that preserve impressions of their soft tissue – their flesh and skin.</p>
<h2>An incredible record of evolution</h2>
<p>These fossil finds involve South Africa in one of the greatest evolutionary stories involving our own distant ancestry. I asked anti-apartheid activist and cleric <a href="http://www.sahistory.org.za/people/archbishop-emeritus-desmond-mpilo-tutu">Archbishop Emeritus Desmond Tutu</a> if he would mind me calling the first new genus <em>Tutusius</em> because I admired his pivotal role in our county’s evolution. </p>
<p><em>Umzantsia</em> is after the isiXhosa word umzantsi, meaning south – it’s doubly relevant because it’s also often used to refer to South Africa.</p>
<p>The country already has the best-preserved specimens <a href="https://www.smithsonianmag.com/science-nature/top-7-human-evolution-discoveries-from-south-africa-158522696/">shedding light on the emergence of humans</a> from pre-human ancestors. Its Karoo region has produced the world’s <a href="https://theconversation.com/why-south-africas-karoo-is-a-palaeontological-wonderland-43045">best series of fossils</a> documenting the evolution of mammals from their reptile-like ancestors. </p>
<p>Now we can add important insights into the evolution of the common ancestors of reptiles and mammals from fish. This means that South Africa has the most complete record through geological time of the origins of our own lineage from fish to humans.</p><img src="https://counter.theconversation.com/content/97747/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The major funders of this project are the Millenium Trust and the DST-NRF Centre of Excellence in Palaeosciences which is based at the University of the Witwatersrand. It also receives funding from the NRF African Origins Platform. Per Ahlberg is funded by the Knut and Alice Wallenberg Foundation in Sweden.</span></em></p>The discovery of two separate fossils tetrapod species proves that they lived all over the world by the end of Devonian.Robert W. Gess, Palaeontologist, Albany Museum, Rhodes UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/914112018-02-08T17:03:19Z2018-02-08T17:03:19Z‘Walking’ fish help scientists to understand how we left the ocean<figure><img src="https://images.theconversation.com/files/205515/original/file-20180208-180805-1giwl5y.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Tiktaalik: bridging the gap between land and sea</span> <span class="attribution"><a class="source" href="https://www.nsf.gov/news/mmg/mmg_disp.jsp?med_id=58310&from=mn">Zina Deretsky/National Science Foundation</a></span></figcaption></figure><p>Our ancestors’ transition out of the water and onto the land was a pivotal moment in evolution. No longer buoyed by water, early tetrapods (animals with four limbs) had to overcome gravity in order to move their bodies. Exactly how those early pioneers first evolved the fundamental capacity to walk has fascinated scientists for many years.</p>
<p>Fossil discoveries can tell us how and when vertebrates evolved the physical features needed to move onto land. But new research <a href="http://bit.ly/2nPG6cZ">published in the journal Cell</a> suggests that the neural circuitry needed to walk probably existed long before actual legs evolved. Because land-based animals and fish share the same circuitry today, their last common ancestor - an ancient fish which existed 420m years ago - probably also had that circuitry and used it to move around beneath the water. </p>
<p>We already have a reasonably good idea of when fish evolved into land-based tetrapods because the fossil record documents the sequence of changes to their bodies. One of the most iconic specimens is <em>Tiktaalik</em>, a “transitional” fossil dating to around 375m years ago.</p>
<p><em>Tiktaalik</em> is special, because though it retains many fish-like characteristics, it also <a href="https://www.nature.com/articles/nature04637">possesses wrist bones</a>, suggesting that it could support itself on its front limbs. Fossils from rocks older than <em>Tiktaalik</em> lack these wrist bones, and are generally <a href="http://www.bioone.org/doi/abs/10.1671/0272-4634(2002)022%5B0487:VDITDS%5D2.0.CO%3B2">more fish-like</a>. Fossils from younger rocks include <a href="https://www.cambridge.org/core/journals/earth-and-environmental-science-transactions-of-royal-society-of-edinburgh/article/devonian-tetrapod-acanthostega-gunnari-jarvik-postcranial-anatomy-basal-tetrapod-interrelationships-and-patterns-of-skeletal-evolution/B2CAA3144A5E5F60C398170B998112BA">more tetrapod-like species</a>, with distinct digits and limbs.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/205508/original/file-20180208-180836-4qb9w6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/205508/original/file-20180208-180836-4qb9w6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/205508/original/file-20180208-180836-4qb9w6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/205508/original/file-20180208-180836-4qb9w6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/205508/original/file-20180208-180836-4qb9w6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/205508/original/file-20180208-180836-4qb9w6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/205508/original/file-20180208-180836-4qb9w6.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">
<figcaption>
<span class="caption">Little skate.</span>
<span class="attribution"><a class="source" href="https://www.nefsc.noaa.gov/rcb/photogallery/skates.html">Page Valentine/USGS</a></span>
</figcaption>
</figure>
<p>But <a href="http://bit.ly/2nPG6cZ">the new research</a> from New York University in the US suggests that fish needed more than just legs to learn how to walk, and in fact evolved the neural circuitry involved much earlier on. The researchers reached this conclusion by studying little skates, fish that move along the ocean floor by <a href="http://onlinelibrary.wiley.com/doi/10.1046/j.1095-8312.2002.00085.x/abstract">moving their hind fins</a> in a left-right pattern, much as we would move our legs when walking.</p>
<p>The researchers found that the neural circuits little skates use for their alternating fin motion are the same as those mice and other four-legged animals use for limb movement. What’s more, this circuitry is produced by similar genes. </p>
<h2>Mind before matter</h2>
<p>Because it is unlikely that the same circuitry evolved twice, this implies that the same genes and neural pathways found in tetrapods and skates were present in their last common ancestor, some 420m years ago. This is long before the earliest fossil evidence for tetrapods, meaning that the circuits involved in walking first evolved millions of years before legs or feet first appeared.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/ay5xCfyGWsg?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>Skates aren’t the only walking fish that still exist today. In fact, it’s fish that are less adapted for life out of water that move in a manner most like walking, where one limb is placed in front of the other. Blind cavefish fall into this group, using their fins <a href="https://www.nature.com/articles/srep23711">to walk on the riverbed</a> and to climb waterfalls. Lungfish, which move somewhat haphazardly on land, also seem to use their fins in <a href="https://www.pnas.org/content/108/52/21146">an alternating pattern</a> to propel themselves along the sediment surface when in water.</p>
<p>Scientists have also been observing how modern fish move over land, without the buoyancy aid provided by water. Obvious choices for such studies are fish that are capable of moving around on land, and regularly do so in nature. Mudskippers, for instance, move by using <a href="https://academic.oup.com/icb/article/53/2/283/806410">their forelimbs like crutches</a> to propel themselves forward. Lungfish, on the other hand, tend to anchor the head and <a href="https://www.nature.com/articles/srep33734">flip the rest of the body forward</a>, which can sometimes leave behind marks that look like footprints.</p>
<p>The new research is an important reminder that however good our fossil record gets, it can only show us the shape or anatomy of an organism. The genetic, neural, and behavioural features that determine what an animal does are ultimately the drivers of that anatomy. The links between living animals can often tell us as much, if not more, about our ancestors as fossilised bones and footprints.</p><img src="https://counter.theconversation.com/content/91411/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Peter Falkingham 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>Little skates that ‘walk’ across the ocean floor show how fish brains evolved to pave the way for working legs.Peter Falkingham, Lecturer in Vertebrate Biology, Liverpool John Moores UniversityLicensed 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/439262015-07-15T04:34:33Z2015-07-15T04:34:33ZAncient plant eating cousins from Brazil and South Africa are reunited<figure><img src="https://images.theconversation.com/files/87382/original/image-20150704-20468-dfudj7.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Artistic reconstruction of two Tiarajudens males during combat in the Permian of southern Brazil.</span> <span class="attribution"><span class="source">Supplied</span></span></figcaption></figure><p>New <a href="http://rsos.royalsocietypublishing.org/">evidence</a> has been provided confirming previous <a href="http://www.nature.com/news/earth-science-how-plate-tectonics-clicked-1.13655">compelling</a> geological findings that today’s continents were once linked in one giant land mass. The evidence has come through the discovery that two fossils, one from South Africa and the other from Brazil, were cousins.</p>
<p>The discovery of a Brazilian plant-eating herbivore fossil in 2008 prompted a restudy of the South African cousin of the same size and with a remarkably similar skull discovered 10 years earlier. These two species from <a href="http://www.livescience.com/37285-gondwana.html">Gondwana</a> – the ancient super continent formed by now separated southern continents such as Africa and South America – show features in their skull and teeth that indicate they were closely related.</p>
<p>Close examination of the two skulls, identified as four-legged or tetrapod animals that date back to a time before dinosaurs existed, revealed two further astonishing facts. The first is that 270 million years ago they were already capable of chewing their food like modern ruminants such as cattle, sheep, goats and deer. </p>
<p>The fossils, which date from what is known as the Middle Permian period, also show that the plant-eating tetrapods had developed two specialisations that they used in combat – a feature typical of today’s cows and deer.</p>
<p>And the most fascinating aspect of all is that these not too distant cousins were found more than 8000 kilometres apart on different modern day continents.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/87380/original/image-20150704-20484-1hc0qj2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/87380/original/image-20150704-20484-1hc0qj2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=297&fit=crop&dpr=1 600w, https://images.theconversation.com/files/87380/original/image-20150704-20484-1hc0qj2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=297&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/87380/original/image-20150704-20484-1hc0qj2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=297&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/87380/original/image-20150704-20484-1hc0qj2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=373&fit=crop&dpr=1 754w, https://images.theconversation.com/files/87380/original/image-20150704-20484-1hc0qj2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=373&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/87380/original/image-20150704-20484-1hc0qj2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=373&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The skulls of Anomocephalus africanus (left) and Tiarajudens eccentricus (right).</span>
<span class="attribution"><span class="source">Supplied.</span></span>
</figcaption>
</figure>
<h2>The deers of yesteryear</h2>
<p>Living mammals have a rich history documented by fossils going back 300 million years. Ancestral lineages of mammals were included in a group known as <a href="http://global.britannica.com/animal/therapsid">therapsids</a> that flourished during the <a href="http://www.ucmp.berkeley.edu/permian/permian.php">Permian</a>, which predated the age of dinosaurs, and are exquisitely documented in the Karoo Basin of South Africa.</p>
<p>Plant-eating animals are now far more diverse and abundant than carnivores, a trend that began during the Permian. A particular group called anomodonts can best be described as the “Permian deers”. Besides being plant-eating and the most abundant lineage of the Permian, anomodonts were extremely variable in size. They were also very different in their shapes, particularly the earliest members of the group.</p>
<p>The Brazilian fossil had some unexpected features for a herbivore. Three stand out. The first is that it had occluding teeth that allowed them to chew, or masticate, food – a feature that is a landmark of today’s mammals.</p>
<p>The second is that it had a long outsized blade-like canine (~120 mm long). This shows, for the first time, the presence of saber-tooth in herbivores mammals around 270 million years ago. Saber teeth are found in some great carnivores from the past such as the <a href="http://www.ucmp.berkeley.edu/synapsids/gorgonopsia.html">gorgonopsians</a> or the <a href="http://www.enchantedlearning.com/subjects/mammals/smilodon/"><em>Smilodon</em></a> sabre-toothed cat, and other Ice Age cats.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/87381/original/image-20150704-20453-1ay1nxr.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/87381/original/image-20150704-20453-1ay1nxr.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=422&fit=crop&dpr=1 600w, https://images.theconversation.com/files/87381/original/image-20150704-20453-1ay1nxr.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=422&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/87381/original/image-20150704-20453-1ay1nxr.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=422&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/87381/original/image-20150704-20453-1ay1nxr.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=531&fit=crop&dpr=1 754w, https://images.theconversation.com/files/87381/original/image-20150704-20453-1ay1nxr.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=531&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/87381/original/image-20150704-20453-1ay1nxr.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=531&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The skull of the Asian water-deer Hydropotes inermis.</span>
<span class="attribution"><span class="source">Provided.</span></span>
</figcaption>
</figure>
<p>But carnivores do not need to chew their food, so that the Brazilian anomodont had several occluding teeth proved that it was a dedicated herbivore after all.</p>
<p>But the surprises did not end there. <em>Tiarajudens eccentricus</em>, the Brazilian species, show teeth that are commonly located at the margin of the mouth, positioned on a bone of the palate. The novelty is that no other therapsid was known to possess teeth in this bone. In fact no other therapsids are known to have complex, molar-like teeth (molariforms) in the roof of their mouths.</p>
<p>After additional cleaning of the bones of the fossil found in South Africa, called <a href="http://rspb.royalsocietypublishing.org/content/266/1417/331.short"><em>Anomocephalus africanus</em></a>, it was found it also had molariforms in the palate, identical to those of <em>Tiarajudens</em>. The South African fossil has a complete mandible and its teeth are in contact with the palate, confirming the occlusion between upper and lower teeth. The only apparent difference between the two fossils is the absence of blade-like canines in the African species.</p>
<p>The skull of these cousins are nearly the same size – between 210 and 220 mm. They show a domed profile with a very short snout, large orbits, and temporal opening for chewing muscles about the same size or slightly larger than the eye socket.</p>
<p>The long canine in the Brazilian species is represented in a few living deer such as the Asian water-deer, musk-deer, and muntjacs. In all these cases the enlarged canines are used in male-male visual displays during fighting. The long canine in <em>Tiarajudens eccentricus</em> is being interpreted as an indication of its use in a similar way, representing the oldest evidence of use of canine in a herbivore for male-male fight.</p><img src="https://counter.theconversation.com/content/43926/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Fernando Abdala receives funding from the National Research Foundation of South Africa.</span></em></p><p class="fine-print"><em><span>Juan Carlos Cisneros receives funding from Conselho Nacional de Desenvolvimento Científico e Tecnológico of Brazil.</span></em></p>New evidence shows marked similarities between two fossils – one from Brazil, the other South Africa. This confirms compelling geological findings that continents were once one giant land mass.Fernando Abdala, Reader, Evolutionary Studies Institute, University of the WitwatersrandJuan Carlos Cisneros, Lecturer in Palaeontology, Universidade Federal do Piauí (UFPI)Licensed as Creative Commons – attribution, no derivatives.