4-Meter Reptile Found in the Belly of Prehistoric Marine Carnivore

When paleontologists digging in a quarry in southwestern China uncovered the nearly complete skeleton of a giant, dolphin-like marine reptile known as an ichthyosaur, they didn’t expect to find another fossil in its stomach. This second skeleton belonged to a four-meter-long, lizard-like aquatic reptile known as a thalattosaur and is one of the longest fossils ever found in the stomach of a prehistoric marine reptile.

Triassic marine reptiles were megapredators

While the researchers can’t say for sure whether the thalattosaur was scavenged or preyed upon, their work could be the oldest direct evidence that Triassic marine reptiles like ichthyosaurs — previously thought to be cephalopod feeders — were apex megapredators. The findings appear in the journal iScience. Co-author Ryosuke Motani, a professor of paleobiology at the University of California. Davis said:

“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. Our ichthyosaur’s stomach contents weren’t etched by stomach acid, so it must have died quite soon after ingesting this food item. 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 stomach of this 240-million-year-old fossil ichthyosaur contains the mid-section of another marine reptile that in life would have been only slightly smaller. It’s the first direct evidence of ancient megapredation — one large animal eating another. (Image: Da-Yong Jiang, et al via iScience)

Because stomach contents are rarely found in marine fossils, researchers rely on tooth and jaw shapes to learn what prehistoric species may have eaten. While prehistoric apex predators are typically thought to have large teeth with sharp cutting edges, some modern predatory species like crocodiles use blunt teeth to consume large prey items with grasping force instead of cutting. Ichthyosaurs share these blunter teeth, but with no direct evidence of large prey consumption in these prehistoric marine reptiles, scientists believed that they fed on small prey like cephalopods.

However, the discovery of the giant thalattosaur in the stomach of the ichthyosaur found by Motani, Da-Yong Jiang, a paleontologist at Peking University in China, and their team suggests that this was not the case, saying:

While the researchers now know that the ichthyosaur could eat animals as large as the thalattosaur, they don’t know if it killed this individual, or simply scavenged it. “Nobody was there filming it,” says Motani. However, there is reason to believe this was not a case of scavenging: Modern marine decomposition studies suggest that if left to decay, the thalattosaur’s limbs would disintegrate and detach before the tail. Instead, the researchers found the opposite in these fossils.