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Uncategorized Friday, August 12th 2011 at 11:29 am

Pregnant Fossil Is First Evidence That Plesiosaurs Gave Birth To Live Young

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For nearly 25 years a spectacular fossil that could answer scientists’ questions about an ancient marine reptile lay buried in the basement of the Natural History Museum of Los Angeles County. The fossil was of a plesiosaur, a large four-flippered creature that roamed the oceans some 78 million years ago. But it wasn’t just any fossil, this fossil was pregnant.

The fossil shows the mother, around 470 cm long, carrying a single fetus, around 150 cm long. The fetus has 20 vertebrae, shoulders, hips and paddle bones, and is believed to be about two-thirds grown. This is the first case of a pregnant plesiosaur fossil, and it shows that the creatures gave birth to live babies rather than hatching eggs. The finding also suggests that the creatures cared for their young similar to modern day whales and dolphins.

The fossil is of a species called Polycotylus latippinus. Unlike some ancient marine reptiles, which would give birth to many small babies, the Polycotylus fossil shows that its reproduction was more like the extinct ichthyosaurs, mosasaurs, and choristoderans which all gave birth to live young.

The analysis of the fossil was led by Robin O’Keefe from Marshall University and Luis Chiappe from the Natural History Museum of Los Angeles County. O’Keefe told Nature News:

“We have known about plesiosaurs for almost 200 years, but despite an excellent fossil record we have never found a pregnant plesiosaur before.”

According to O’Keefe, because the fossil shows that the plesiosaur would have given birth to a single baby, it is likely that the creatures had some sort of social dynamic where they would care for their young. There is a precident for large animals that give birth to a single child to care for it the way humans, elephants, whales, or dolphins do. Also, the fossil shows that the baby was not fully developed with some unfused bones that would have made it vulnerable and unlikely to be able to care for itself at birth. This suggests some sort of social group where mother and baby could have received protection. O’Keefe says:

“If you are going to put all your egg in one basket by having a single large baby, it makes a lot of sense that you would want to take care of that baby.”

However, this is the first fossil ever found of a pregnant plesiosaur. Sweeping conclusions can not and have not been made about the creatures social life. More fossils would be needed to determine if the plesiosaur had a different social and reproductive life than other extinct marine reptiles.

The fossil was discovered in Kansas in 1987 by a private fossil hunter and donated to the museum, where it sat without being analyzed or prepared for show. Last year the museum decided to dust off the fossil, and obtained the necessary funding for its preparation and display. For those interested in checking out a bit of history, the museum’s new dinosaur hall now has the fossil, nicknamed Poly, on display. The research was published in the journal Science.

(via Nature News, image via Natural History Museum of Los Angeles County)

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  • http://www.facebook.com/j.pedro.ramirez Jose Pedro Ramirez

    Rare find, good news.  Anything else about it?

  • http://www.facebook.com/j.pedro.ramirez Jose Pedro Ramirez

    It is rare to find fossils and still more rare to find a pregnant fossil.  What good news!

  • Anonymous

    Wouldn’t that make the Plesiosaur a mammal

  • drice

    no sharks give birth to live young also

  • Austin Sostack

    there are other non-mammals even today that have live-births.Such as some vipers and boa constrictors.

  • Toddmo

    some sharks bear live young, some lay sailors purses

  • Advice

    some sharks Do give birth to live young and some lay eggs. some of the eggs were called Sailors’ Purses due to their appearance.

  • Michael Franklin

    This is an amazing discovery, though I must admit that I was under the impression that the Plesiosaur was a true Dinosaur. it is not and so I have had to chase down all my comments to apologize, lol.

    What I am most astounded by, though, is that this animal died and was buried in her pregnant state. This means that there was no time for any kind of trauma-induced premature birth… or any noted predatory action on her carcass after death. In sum, whatever happened, it buried her and her unborn calf in such an instant, that she and the baby were frozen in time.

    What kind of catastrophe could lead to this? It makes for a wonderful train of thought! 

  • http://www.facebook.com/people/Benjamin-Stewart/1180783446 Benjamin Stewart

    This is how they did X-rays back then.

  • http://www.facebook.com/people/Ammie-Hisaka/100001798512605 Ammie Hisaka

    Isn’t it morely to be just the bones of a creature that thing ate?

  • http://www.facebook.com/profile.php?id=100000416149823 Hannah Wick

    Yes, it somehow managed to consume a 2/3 developed fetus of one of it’s own species.

    Somehow.

  • http://www.facebook.com/people/Ammie-Hisaka/100001798512605 Ammie Hisaka

    It’s a jumble of bones, how can they even tell what species it is, let alone how developed it might or might not be?

  • http://pulse.yahoo.com/_Z4CJFSWSF6NJQ2QO56FEBHKHJM K

    And are you insinuating the echidna isn’t a mammal?  Nooo

  • http://pulse.yahoo.com/_Z4CJFSWSF6NJQ2QO56FEBHKHJM K

    Dude, sometimes births just don’t happen.  Pregnant mammals (including humans) die pregnant without giving birth all the time.  A friend just had a baby by caesarean section – her cervix never dilated, the baby never dropped to birthing position, and she was rapidly approaching kidney-failure stage level of preeclampsia.  In nature she would have died a horrible, painful death, with the fetus inside her.

    Predatory/consumptive action may still have occurred, as well – the fossil is just bones, right?  Marine environments are especially ripe with organisms that burrow through soft tissues rather than ripping apart animals with such force their bone break

  • http://pulse.yahoo.com/_Z4CJFSWSF6NJQ2QO56FEBHKHJM K

    I normally don’t do this…but I just have to say, you comment is *especially* retarded.

  • http://pulse.yahoo.com/_Z4CJFSWSF6NJQ2QO56FEBHKHJM K

    If you look at the picture sideways, it kind of looks like the mom’s playing basketball with the baby.

  • Michael Franklin

    Of course, there’s no way to know for sure. But the evidence is there to suggest something more than a slow, boring death… not unlike the mammoth that was flash-frozen with buttercups still in its mouth. A snapshot in time, so to speak.

    Dute, I wasn’t really looking for a debate… was just sharing a few thoughts :)

  • http://twitter.com/Apple_Lollipops AppleLowe

    That is kinda a giant chunk of their job.  If they couldn’t tell what species it is and make reasonable deductions about how it developed then they wouldn’t have been hired by a museum by paleontologist.  Instead they would just be people who like collecting pretty looking fossils.
    I have no idea if you just don’t get paleontology or if you are just used to thinking of fossils as massive well put together skeletons.  Either way welcome to the actual field of paleontology.  Fossils don’t pop out of the ground fully formed and ready to hang in a museum. That’s what most fossils look like.  Figuring out what fossilized remains is an incredibly difficult job but that doesn’t make it impossible.

  • Anonymous

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  • Anonymous

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  • http://www.facebook.com/TheSilverUnicorn Shawna Lynn

    My guess is that the paleontologists involved in this project explored that possibility and rejected it as an unlikely explanation. For example, if the larger creature had eaten the smaller one, then it’s digestive juices would have left chemical scarring on the bones (left some evidence of at least partial digestion). A lack of such scarring would make it highly unlikely that the smaller creature was swallowed. I’m sure they examined a number of different theories before arriving at what they believed to be the most reasonable interpretation of the fossil evidence.

  • http://www.facebook.com/TheSilverUnicorn Shawna Lynn

    Nearly all fossils are just that, a jumble of bones. This is a better jumble of bones than most because it is preserved in a relatively recognizable arrangement. Many fossils are just bone fragments, yet paleontologists are still able to identify them.