This 15-Foot Ichthyosaur Died With a 13-Foot Meal in Its Stomach

The shocking size of the marine predator’s quarry may force paleontologists to rethink the marine reptile’s role in the Triassic ecosystem

ichthyosaur's last meal
The stomach of a 15-foot fossil ichthyosaur excavated in China contained this massive chunk of another large marine reptile. The ichthyosaur swallowed its prey shortly before it died and was fossilized. Da-Yong Jiang, et al.

When paleontologists dug up a 15-foot marine reptile called an ichthyosaur in southwestern China, they got more than they bargained for. Around 240 million years ago, the same may have been true for the ichthyosaur.

The huge marine predator died and fossilized with the entire torso of another 13-foot-long swimming reptile called a thalattosaur lodged in its gut, creating the fossil equivalent of nesting Russian dolls, reports Jason Bittel for National Geographic. It’s impossible to tell whether the ambitious ichthyosaur was done in by a case of its eyes being bigger than its tummy, but what’s for sure is that we didn’t understand the ichthyosaur diet quite as well as we thought we did.

The ichthyosaur’s teeth are peg-like and not terribly sharp, which paleontologists thought meant it chowed down on soft, slippery prey like cephalopods.

“Now we have really solid evidence saying these [blunt] teeth can be used to eat something big,” Ryosuke Motani, a paleobiologist at the University of California, Davis and lead author of a new study of the fossil, tells Maria Temming for Science News. “That means the other species with similar teeth we discounted before … may be megapredators too.”

Instead of sawing through large prey with sharp, serrated teeth similar to those seen on modern great white sharks, the ichthyosaur may have ripped its prey apart more like orcas or crocodiles, which also have cone-shaped teeth.

The extraordinary fossil was first unearthed in 2010 in the Guizhou province in southwestern China. The ichthyosaur is of the genus Guizhouichthyosaurus and would have looked something like a large dolphin with long slender jaws. The slightly shorter and much slimmer thalattosaur, called Xinpusaurus xingyiensis, was more like a giant swimming lizard with four paddle-like limbs.

The researchers, who published their findings last week in the journal iScience, say they can’t be certain whether the ichthyosaur killed the thalattosaur or merely scavenged it. However, the fact that such a large, contiguous morsel of the meal is permanently bulging out of the predator’s stomach may tip the scales.

“If a predator other than Guizhouichthyosaurus killed the thalattosaur in question, then it would be strange for the nutritious trunk and limbs to be left intact by the predator,” the team writes in the paper. Another fossil that appears to be the discarded tail of the thalattosaur was found in sediments nearby, according to a statement.

This 15-Foot Ichthyosaur Died With a 13-Foot Meal in Its Stomach
This diagram shows the section of the 13-foot thalattosaur that was found inside the roughly 15-foot ichthyosaur. Da-Yong Jiang, et al.

Nick Fraser, a palaeontologist at National Museums Scotland who was not involved with the study, tells Nicola Davis of the Guardian that the paper presents a convincing case that Xinpusaurus was Guizhouichthyosaurus’ last meal and that the ichthyosaur probably made the kill itself.

“In any event, I think it is clear that it was a step too far for the ichthyosaur,” Fraser tells the Guardian. “As such this might represent a rather uncommon event in a day in the life of a Triassic marine reptile. But it does rather magically bring to life a cameo of animal interactions in the seas approximately 230 million years ago.”