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Big bang theory: how did dinosaurs have sex?

Dinosaurs were the largest animals to ever walk Earth, and they ruled the planet for more than 160 million years. The long-necked Argentinosaurus, with back vertebrae almost two metres high, possibly grew…

Debate continues over how dinosaurs did the deed. Miroslav Petrasko (blog.hdrshooter.net)

Dinosaurs were the largest animals to ever walk Earth, and they ruled the planet for more than 160 million years. The long-necked Argentinosaurus, with back vertebrae almost two metres high, possibly grew to 30 metres long and weighed up to 80 tonnes. So did the earth really shake for them when they mated?

The real question here though is: how did they really mate and what evidence do we have to reconstruct their sex lives?

The internet offers vague speculation. One website claims they probably didn’t have penises so must have used cloacal kissing, juxtaposing their massive bottoms together for the interchange of seminal fluid to the female, as do most frogs and many birds.

I disagree with this view, as evidence from living animals, close relatives of dinosaurs, implies they must have mated using copulation, and that the male must have had very large and flexible penises.

Ainvar Photography

We now know with confidence that the meat-eating theropods, such as Tyrannosaurus and kin, were the group that gave rise to the first birds about 160 million years ago.

This is established from a large number of exquisite fossils showing various feathered dinosaurs and early dinosaur-like birds from sites in northern China.

Crocodiles and their kin evolved from the last common ancestor of the dinosaur-bird group, so crocs can’t be regarded as “descendents of the dinosaurs” as some crocodile park ads would have us believe.

All male crocodiles have a penis and most primitive living birds also possess one, so it follows that dinosaurs must also have had a penis. The majority of living birds though have secondarily lost the penis. For them a mating is a simple, quick cloacal kiss where sperm is rapidly passed to the female.

Once all the fancy dancing and singing is done, the sexual act can be over in a second or less in some birds, such as dunnocks, shown in the video below:

Doing it dunnock style.

So how did the dinosaurs do it? Biomechanics experts such as Professor McNeill Alexander of The University of Leeds claim that the weight of the male would have rested on the females hips to mount from behind as elephants do, but the resulting stresses would have been massive.

Professor Roger Seymour from the University of Adelaide studied giraffes mating (see video below) and proved that the male’s blood pressure is roughly twice that of other mammals. Their hearts need be proportionately 75% larger due to the physiological constraints of the long neck and highly perched head.

A high-pressure situation.

Bearing this in mind, he suggested that, for long-necked dinosaurs, they could only have mated in a particular way. A dinosaur with, say, a ten-metre-long neck would have seven times the normal mammalian blood pressure. So rear mounting is not a big problem if one keeps the neck horizontal.

Just imagine a 70-tonne giant sauropod fainting after loss of blood pressure to the head at the time of orgasm while mounting its mate. Yes, the earth would have most certainly shaken for them.

New clues

Recent molecular studies of the major bird groups find that the ostriches and other primitive flightless birds are indeed the most ancient members of the living birds, with ducks and geese and some other waterbirds also very old lineages.

All these primitive living birds possess a penis, with ducks having the most bizarre types – a regular sized Argentine lake Duck has a corkscrew-shaped organ with a brush on the tip that measures up to 42 cm long.

Muscovy ducks can also explosively evert their penises in 0.3 second to 20 cm long - roughly the same speed as driving at 70kph – as can be seen in the video below:

Duck and cover.

So, it’s quite likely their distantly extinct ancestors, the meat-eating theropod dinosaurs also mated using an eversible penis, most likely a terrifyingly large one.

For an animal the size of Tyrannosaurus (14 metres long) to mate effectively the male organ would need be in the order of at least two metres long, and maybe a lot more if it happened to be cork-screw shaped like a duck’s.

It’s not unlikely that one day palaeontologists will find a fossilised dinosaur penis. Extraordinary soft-tissue preservation in fossils are coming to light each year along with new fossil sites being discovered.

Greater detail can be resolved in fossils using new technologies, such as micro-CT and synchrotron tomography. Recently, 380 million-year-old fossil fishes from Australia were found to have complete sets of muscles preserved.

A small dinosaur fossil found in the spring of 1981 in central Italy, named Scipionyx, revealed excellent soft tissue preservation, with clear impressions of the intestines, liver and some muscles. Such fossils offer hope.

I truly believe the day will surely come, probably when we least expect it, when a remarkable new dinosaur fossil pops up solving the age old mystery of how dinosaurs really did do the deed.

Join the conversation

9 Comments sorted by

  1. George Michaelson

    Person

    If Ostriches have a penis but also lay eggs via a cloaca, then does this mean there is no bone anatomy which can be used to confirm the presence or absence of penis in dinosaurs? Surely the musculature would have anchor points and leave bone scars, to support a 2m corkscrew with bottle-brush ending?

    And if erectile tissue demands blood supply, wouldn't the relative size of blood channels through the pelvic bones indicate?

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    1. John Long

      Strategic Professor in Palaeontology at Flinders University

      In reply to George Michaelson

      Very good points. Ostriches, and in fact all birds that have a penis, lack an 'os baculum'or penis bone, only found in some groups of mammals. Pelvic bones do however anchor penis muscles in many groups but the nature of their attachment scars to identify penis musculature has not been fully investigated to confirm or deny such muscles existed in dinosaurs. Second point is that in birds erection of the penis is not via pumping of blood but using lymph fluids, so there would be no evidence from the vascular canals of the pelvic bones (most of which flow around, not through, pelvic bone foramina).

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  2. Rory Cunningham
    Rory Cunningham is a Friend of The Conversation.

    Test Analyst

    If there is still speculation about mating in dinosaurs, how well do those dinosaur documentaries (walking with dinosaurs etc.) protray actual dinosaur habits in general?

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    1. John Long

      Strategic Professor in Palaeontology at Flinders University

      In reply to Rory Cunningham

      These documentaries are reconstructions of behaviour based on leading palaeontologists who best estimate what is known of behaviour in their closest living relatives (crocodiles and some birds), plus actual evidence from fossils-eg trackways of dinosaurs that show behaviour (herding, pretecting young etc), stomach contents indicating diet, biomechanics of their skeletons indicating the limits and speeds of their walking or running capability, agility and so on.

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  3. Dale Bloom

    Analyst

    This website must have the all time record for articles on penises, and when will academics ever think of maleness as being more than a penis?

    Articles such as “Where are the Willies? The Missing Penis in “Magic Mike””, to “Who keeps the penis? Slugs and the battle of the sexes” to “The human penis is a puzzler, no bones about it”, to Squid or swallow: the sexual tastes of a cephalopod” etc.

    Most articles are totally juvenile and written to mock or denigrate the male gender, regardless of species.

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    1. Tim Benham

      Student of Statistics

      In reply to Dale Bloom

      I don't see anything objectionable about this article, Dale, and I'm as MRM as anyone.

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    2. Venise Alstergren
      Venise Alstergren is a Friend of The Conversation.

      photographer, blogger.

      In reply to Dale Bloom

      For heaven's sake, Dale Bloom, why is it offensive to read articles about the male penis when whole libraries could be filled with articles about women's tits?

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    3. Dale Bloom

      Analyst

      In reply to Tim Benham

      In all the voluminous writting about penises in The Conversation, I have never once seen it stated what a penis is actually designed for, which is to deposit sperm close to the female cervix.

      I concur that the voluminous writing about penises is not being done for any scientific purpose.

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  4. Kelvin Yin

    PhD student

    I agree that dinosaurs wouldn't have cloacal kissed simply because they'd have too many teeth for it.

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