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

Paleontologists in southwest China recently discovered an almost complete skeleton of a prehistoric marine reptile known as the ichthyosaur. But they also found something completely unexpected – a well-preserved and extremely long reptile inside this creature’s belly.

Ichthyosaurs were giant dolphin-like carnivores that lived during the dinosaur era, thriving during the Mesozoic era. In a study published Thursday in the journal iScience, researchers documented finding one with a fossil in its stomach belonging to an aquatic reptile resembling a four-meter-long lizard called a thalattosaurus.

It is one of the longest fossils ever found in the stomach of a prehistoric marine reptile. Researchers said the predator likely died soon after ingesting its prey, which could explain why it is so well preserved.

This last meal took place during the Middle Triassic period, around 237 to 247 million years ago.

It is quite rare to find fossils in the stomachs of other fossils, so researchers usually rely on the shape of teeth and jaws to infer the diets of prehistoric species. While apex predators tend to have large, sharp teeth, those of ichthyosaurs were more blunt, leading researchers to believe that they primarily preyed on small prey like cephalopods.

“If you look at all the similar marine reptiles that lived in the dinosaur age, we actually never found anything articulate like this in the stomach,” study co-author Ryosuke Motani , professor of paleobiology at the University of California, Davis, said in a press release. “At first we just didn’t believe it, but after spending several years visiting the dig site and looking at the same specimens, we were finally able to swallow what we saw.”

The new finding could reclassify the species as “top mega-predators” – predators at the top of the food chain.

“Now we can seriously consider that they were eating large animals, even when they had clenched teeth,” Motani said. “It has already been suggested that maybe a sharp edge isn’t crucial, and our finding really supports that. It’s pretty clear that this animal could process this big food using dull teeth.”

However, it is still unclear whether the ichthyosaur killed the thalattosaurus or whether it simply recovered it.

“No one was there to film it,” Motani joked.

But researchers doubt this is a case of recovery, given how far they found the thalattosaurus fossil intact. If it was a case of recovery, they said, its limbs would have decomposed; however, its limbs were at least partially attacked and it appears that its tail was torn off.

The researchers said that regardless of how the ichthyosaur ate its last meal, the finding is the oldest direct evidence that the species ate larger animals than modern humans.

“We now have a really solid articulated fossil in the stomach of a marine reptile for the first time,” Motani said. “We used to guess that they must have eaten these big things, but now we can say for sure that they ate big animals. It also suggests that megapredation was probably more common than we previously thought.

Researchers are studying the quarry where the pair of fossils was found for more than a decade. It was opened as a museum, but excavation projects are still ongoing.

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