Scientists discover 200-million-year-old embryo in ichthyosaur fossil

Scientists have discovered a giant water-dwelling reptile that roamed the oceans 200 million years ago was pregnant at the time of its death.

The Ichthyosaurus somersetensis fossil, which was housed at Lower Saxony State Museum in Hanover, Germany, is the largest of its species — it would have measured between 3 and 3.5 metres when alive. But that didn't mean the embryo was easy to spot for the untrained eye.

Discovered near Somerset, England, in the 1990s, the fossil had remained unstudied — that is, until paleontologist Sven Sachs of the Bielefeld Natural History Museum came across it in January. He contacted fellow paleontologist and ichthyosaur expert Dean Lomax who found the specimen intriguing.

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"I was really excited after receiving the photographs," Lomax told CBC News. "I was blown away by the size of the specimen, because most of these examples of ichthyosaurs are about between 1 to 2.5 metres."

But Lomax said he "instantly" spotted something that others had missed: a seven-centimetre spinal column belonging to an embryo.

Connecting the dots

While at first glance the ichthyosaur may resemble marine animals of today such as dolphins and sharks, they're actually more closely related to reptiles.

"Dolphins would be closer to humans than they would be to ichthyosaurs," Lomax said.

There are many different types of ichthyosaurs, with one of the largest — measuring 23 metres — discovered in British Columbia in 1999. The ancient marine animals thrived in the Triassic and Jurassic periods and are believed to have gone extinct roughly 90 million years ago.

What's interesting about ichthyosaurs, Lomax notes, is that some species have been found with as many as eight embryos, while others — such as this one — have had only one. This leaves paleontologists wondering if all species of ichthyosaurs were capable of carrying multiple embryos or just some.

Michael Caldwell, who was not involved in this study, knows ichthyosaurs well: in 2006 he and a graduate student at the University of Alberta found a 100-million-year-old specimen in box buried under a ping pong table at the university. 

"One of the great things about finding embryos is that we can learn a great deal about the development of an organism," Caldwell, a professor and chair of biological sciences at the university, told CBC News. "It's nice to see dots getting connected together."

The embryo, the authors noted in the study published in the journal Acta Palaeontologica Polonica, is incomplete, but contains part of the back bone, a forefin, ribs and some other bones. 

And, while examining the fossil, the paleontologists made another curious discovery: the tail of the specimen belonged to a different ichthyosaur, likely tacked on to make it more visually appealing for the display.

Lomax, who is fascinated with ichthyosaurs, said he's quite pleased with the discovery and hopes it will shed light on other ichthyosaurs.

"To find another specimen like this, which had been in a museum for a good number of years...it's quite spectacular," Lomax said.