Well-preserved giant reptile found in the belly of a prehistoric “megapreditor”

Paleontologists in southwestern China recently discovered an almost complete skeleton of a prehistoric marine reptile known as an ichthyosaur. But they also found something completely unexpected – a well-preserved, extremely long reptile in the stomach of that creature.

Ichthyosaurs were giant, dolphin-like carnivores that lived during the time of the dinosaurs, and flourished during the Mesozoic period. In a study published Thursday in the journal iScience, researchers documented one with a fossil in its stomach that belonged to a four-meter-long, lizard-like egg white reptile called a thalattosaur.

It is one of the longest fossils ever found in the stomach of a prehistoric marine reptile. Researchers said the predator probably died shortly after eating its prey, which may be why it has been so well preserved.

This last food took place back in the Middle Triassic period, roughly 237 million to 247 million years ago.

This image shows a close-up of the stomach area of ​​the ichthyosaur.

Jiang et al.

It is quite rare to find fossils in the stomachs of other fossils, so researchers typically rely on teeth and jaw shapes to dedicate the diets of prehistoric species. While the apex predators have most of large, sharp teeth, those of ichthyosaurs were blunt, some leading researchers believe they mostly feed on small prey such as kephalopods.

“If you look at all the similar marine reptiles that lived in the time of dinosaurs, we never actually found anything articulated like this in the stomach,” study co-author Ryosuke Motani, a professor of paleobiology at the University of California, Davis, said in a press release. “At first we just did not believe it, but after several years of visiting the dig site and looking at the same specimens, we finally knew what we were seeing.”

The new discovery could reclassify the species as “apex megapredators” – predators at the top of the food chain.

ichthyosaur dinosaur fossil teeth
This image shows the teeth of the ichthyosaur.

Jiang et al.

“Now, we can seriously consider that they ate large animals, even when they had teeth,” Motani said. “It has previously been suggested that perhaps a cutting surface was not crucial, and our discovery really supports that. It is quite clear that this animal was able to process this large food with blunt teeth.”

However, it is still unclear if the ichthyosaur killed the thalattosaur or simply killed it.

“Nobody was there during the filming,” Motani joked.

But researchers doubt that this was a case of scavenging, given how intact they found the fossil of the thalattosaurus. If it was a case of scavenging, they said, his limbs would have decayed; however, his limbs were at least partially attacked and it appears that the tail was broken off.

Body configurations of the predator (Ichthyosaur) and prey (thalattosaur).

Jiang et al.

Researchers say that no matter how accurately the ichthyosaur consumes its final meal, the discovery marks the oldest direct evidence that species eat larger than modern humans.

“We now have for the first time a really solid articular fossil in the stomach of a marine reptile,” Motani said. “Before we suggested they should have eaten these big things, but now, we can safely say they ate big animals. This also suggests that mega-predation was probably more frequent than we previously thought.”

Researchers have studied the tomb where the few fossils were found for more than a decade. It was opened as a museum, but the excavation projects are still ongoing.

“Still, new things are coming out,” Motani said. “At this point, it’s above our initial expectations, and we’ll just have to see what we’ll discover next.”