National Geographic News
A photo and an illustration of a fossil.

Fossil of Chaohusaurus reveals a baby inside its mother (orange) and another stuck in her pelvis (yellow).

PHOTOGRAPH AND ILLUSTRATION BY RYOSUKE MOTANI, UC DAVIS

Christine Dell'Amore

National Geographic

Published February 12, 2014

The oldest embryos of a Mesozoic marine reptile have been unearthed in China, pre-dating the previous record by ten million years, a new study says.

The 248-million-year-old fossil from the Mesozoic era (252 to 66 million years ago) reveals an ichthyosaur baby inside its mother (orange) and another stuck in her pelvis (yellow). A third embryo discovered nearby suggests it was stillborn; scientists believe the mother died during a difficult labor.

The narrow, eel-like ichthyosaur belongs to the genus Chaohusaurus and is the oldest known species of the group. (Also see "Pictures: Oldest Dinosaur Embryos Show 'Big Surprises.'")

The findings were published February 12 in the journal PLOS ONE.

It's not just the age of the Mesozoic-era discovery that is surprising; it's the shattering of the belief that ichthyosaurs—also dubbed sea monsters—gave birth in water, not on land.

The scientists reached their conclusion because the fossil showed the offspring emerging head-first—a behavior found only in animals that give birth on land. The babies of most marine animals, such as whales and sea cows, are born tail-first. (Explore an interactive sea-monster time line.)

"That was a big surprise. Initially I couldn't believe my eyes when I saw that," said study leader Ryosuke Motani, a prehistoric marine reptile expert at the University of California, Davis.

Land Birthing

As a rule, reptiles lay eggs and mammals give birth to live young, a strategy known as viviparity. But new research reveals that over the evolutionary trajectory of reproduction, reptiles veered back and forth between the two strategies before settling on egg-laying.

Live birth in reptiles seems to have evolved more than a hundred times in history. But there are many gaps in scientific knowledge surrounding the phenomenon in ancient sea reptiles.

Since ichthyosaurs evolved first on land before becoming aquatic, some of the first species to live in water, such as Chaohusaurus, were still giving birth as their ancestors had—on land. (Read "When Monsters Ruled the Deep" in National Geographic magazine.)

So "live bearing did not evolve in water as scientists thought," said Motani, who worked with scientists at Peking University and Anhui Geological Museum. "Our assumption was wrong."

Follow Christine Dell'Amore on Twitter and Google+.

34 comments
Kyle Alvague
Kyle Alvague

i know i'm just a kid in all but i do believe that this ocean reptiles evolution has changed all of paleontologists research about this reptile and i do believe has changed the reptiles for some to give birth and has became one of all our ancestors to first give birth head first and may have caused mammals to evolve from reptiles to mamemals

Maria Aguilera
Maria Aguilera

Very interesting! discoveries like this one teach us a lot about our planet & ourselves.

Владимир Предоев
Владимир Предоев

I strongly disagree with this article. First of all - sea monster is not quite right when you describe a water dwelling reptile. This animal actually existed and we can prove it. Sea monster is referred to all the creepers that we presumably have seen but we haven`t any kind of proof about it. Second - how on earth would you assume that a fully aquatic animal like an Ichthyosaur, or a modern whale or dolphin is able to give birth on land. Once it loose the buoyancy support of the water it` internal organs will literally collapse under their own weight. Try to give birth lying on your back with a 100 kilograms on your belly. Second this particular fossil is an example of a breech birth. That`s why mother has died. When an animal gives birth it`s absolutely mandatory to ensure survival of the newborn. That`s why land animals bear head first, and aquatic creatures bear tail first. Even sharks are born tail first. It`s basic logic people - if a newborn is air-breather it`s doomed if head comes first. I`d advise the author to review this article once more and to rewrite it in a more acceptable way. 


About the theory that marine reptiles were once laid eggs - modern turtles crawl out of the water to dig a hole in the sand and lay their eggs there. No air-breathing water dwelling creature lays eggs IN the water. 

John Stell
John Stell

Doesn't anyone care what happened that a dinosaur could be so exquistely preserved in the middle of giving birth? 

Gloria A.
Gloria A.

This is like so interesting!!! 

heather Shine
heather Shine

Is it possible the baby was breach, thats why the mom died??

craig hill
craig hill

Fantastic findings. The glory of science.

Jalish Riyad
Jalish Riyad

@People, it is really easy to refute what scientists find in the studies by posting questions here  (some of them logical enough). Still, when they write a paper they address all the related questions that might arise and try to answer that. If they can't, they state that clearly that "this and that needs further studies and insight." Moreover, there are reviewers out there who try to find every shortcoming a paper can have before publishing it. These reviewers are the experts in that field, not just normal scientists. So I believe the most fruitful thing to do would be to go and read the paper (if you have relevant background) or find the author and send him/her an email. No hard feelings please. It is great to see so many people interested about paleontology here. But if you really are not satisfied with the logic your other fellow readers are showing here, then the best thing to do is to ask it directly to the author. That would meet your intellectual thirst, plus you can then spread them (if it seems logical enough to you).

Thanks. Hail science.

Andy Rairigh
Andy Rairigh

How do we know this wasn't a mother shielding her young as they were burried alive?

Timothy Jones
Timothy Jones

Most of your extinct marine reptiles were air breathing, and most of them like the Ichthyisauraus could not venture onto land because of the way their bodies were built. They had to birth their young in the water. Perhaps these ancient reptiles incubated their egg inside until they hatched, then birthed the live into the water as a survival technique.

Thomas Hart
Thomas Hart

OK, call me crazy, but is flies in the face of every dinosaur we know laid eggs.  How about eggs not actually being laid for some reason got stuck inside, the eggs hatch inside and feed off their mom.  Prove that couldn't have happened, then I might believe it, but reporters using the term sea monster don't incite a high level of confidence.

Peter Fessel
Peter Fessel

Is the public really so stupid that you must say "sea monster" instead of "dinosaur" to get anyone's attention?

Tim Morris
Tim Morris

@Владимир Предоев  Pig-nosed Turtles (Carettochelys), lay their eggs in sandbanks. When the sandbank is flooded in the monsoon, this actually activates the hatching of the eggs. Water causes the animals to hatch. This strategy could conceivably also work in a hypothetical proto-ichthyosaur, where an egg is retained with the developing young, and laid into the water after gestation, the egg would hatch upon contact with the water, and the young would emerge. This could be a concievable first step for a proto-ichthyosaur, but more likely, ovoviparity and oviparity are interchangeable, as in modern reptiles, even within one species. Some upland populations of skink give live birth, whilst lowland populations lay eggs.


I think a water-activated egg could perhaps be how Thalattosuchians gave birth, unless they still buried their eggs, which would explain their relatively large hind-flippers.

Lori Young
Lori Young

@Jalish Riyad  Exactly! The article contains a link to the paper, and the questions asked here are addressed in the paper. An example:

"It is likely that newborns were expelled headfirst, given the uniform orientation of the embryonic skulls and the lack of room for reorientation of embryos. It is unlikely that all three individuals represent a breech condition. For example, if a possibility of breech is, say, 10%, then chances of having three consecutive breech births is only 0.1%."

Yup. Hail science.

Glen Wheeler
Glen Wheeler

@Thomas Hart The baby found nearby pretty much eliminates the eggs hatching inside theory. All of the babies would have been stuck inside the mother as the egg chute (not present) would have evolved to let eggs out, not babies. Also, there was no sign of egg shells which are easily preserved and would have been evident inside the mother. There is nothing at all to suggest that this reptile laid eggs.

Tim Morris
Tim Morris

@Thomas Hart  An icthyosaur is not a dinosaur, it is a sea reptile. It is referred to as a sea monster because it kind of is.

Thomas Hart
Thomas Hart

OK, I am an idiot, many do not lay eggs, but do live births.  Still, my scenario is plausible.

Francine Brewin
Francine Brewin

@Peter Fessel  there is a distinction between the two,  The dinosaur was a LAND reptile. The ichtyosaur is related to water dwelling reptile.

Robert Airdrie
Robert Airdrie

@Peter Fessel Sea monster is an inappropriate term, I agree, but so is dinosaur as ichthyosaurs, like other marine reptiles and the pterosaurs, were not dinosaurs.

M de Rijk
M de Rijk

Your scenario would kill the mom, which would produce more fossils where the adult shows signs of this. There would most likely not be any evolutionary advantage. Even some shark species have their eggs hatch in the mother and they eat each other but don't harm the parent. Off course if you can back your theories up with evidence, well.....

A Thomas Tran
A Thomas Tran

 @Peter Fessel  I would rather an 8yo kid reading this be interested in "Sea Monsters" giving live-birth like mammals do,  than that same kid bypassing this article about a strangely named "Ichthyosaur" s/he never heard of.   If the title gets more kids (and even adults) into science, who cares what they call it?


Besides, it is clarified in the subtitle, and @Robert Airdrie I don't think they said the Ichthyosaur was a dinosaur in the text.

Share

How to Feed Our Growing Planet

  • Feed the World

    Feed the World

    National Geographic explores how we can feed the growing population without overwhelming the planet in our food series.

See blogs, stories, photos, and news »

The Innovators Project

See more innovators »

Latest Photos Galleries

See more photos »

Shop Our Space Collection

  • Be the First to Own <i>Cosmos: A Spacetime Odyssey</i>

    Be the First to Own Cosmos: A Spacetime Odyssey

    The updated companion book to Carl Sagan's Cosmos, featuring a new forward by Neil deGrasse Tyson is now available. Proceeds support our mission programs, which protect species, habitats, and cultures.

Shop Now »