Well-preserved giant reptile found in the belly of a prehistoric "megapredator"
Paleontologists in southwestern China recently discovered a nearly complete skeleton of a prehistoric marine reptile known as an ichthyosaur. But they also found something completely unexpected — a well-preserved, extremely long reptile inside that creature's belly.
Ichthyosaurs were giant, dolphin-like carnivores that lived during the time of the dinosaurs, 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 a four-meter-long, lizard-like aquatic reptile called a thalattosaur.
It's 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 be why it is so well preserved.
This last meal back took place back in the Middle Triassic period, roughly 237 million to 247 million years ago.
It's quite rare to find fossils within the stomach of other fossils, so researchers typically rely on tooth and jaw shapes to deduce the diets of prehistoric species. While apex predators tend to have large, sharp teeth, those of ichthyosaurs were blunter, leading researchers to believe they mostly fed on small prey like cephalopods.
"If you look across all the similar marine reptiles that lived in the age of dinosaurs, we've actually never found something 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 didn't believe it, but after spending several years visiting the dig site and looking at the same specimens, we finally were able to swallow what we were seeing."
The new discovery could reclassify the species as "apex megapredators" — predators at the top of the food chain.
"Now, we can seriously consider that they were eating big animals, even when they had grasping teeth," Motani said. "It's been suggested before that maybe a cutting edge was not crucial, and our discovery really supports that. It's pretty clear that this animal could process this large food item using blunt teeth."
It's still unclear, however, whether the ichthyosaur killed the thalattosaur or simply scavenged it.
"Nobody was there filming it," Motani joked.
But researchers doubt that this was a case of scavenging, given how intact they found the fossil of the thalattosaur. If it was a case of scavenging, they said, its limbs would have decayed; however, its limbs were at least partially attacked and it appears its tail was ripped off.
Researchers said that, regardless of how exactly the ichthyosaur consumed its final meal, the discovery marks the oldest direct evidence that the species ate animals larger than modern humans.
"We now have a really solid articulated fossil in the stomach of a marine reptile for the first time," Motani said. "Before, we guessed that they must have eaten these big things, but now, we can say for sure that they did eat large animals. This also suggests that megapredation was probably more common than we previously thought."
Researchers have been studying the quarry where the pair of fossils was found for more than a decade. It has been opened as a museum, but the 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'll discover next."
