Aug. 20 (UPI) -- Until now, scientists thought ichthyosaurs -- the large, dolphin-like marine reptiles that cruised the seas of the Mesozoic -- mostly ate cephalopods.
"Many of the large ichthyosaurs have blunt teeth that look more suited for squid-eating than megapredation," researcher Ryosuke Motani, professor of paleobiology at the University of California, Davis, told UPI in an email. "That is why we thought they were squid eaters."
But recently, Motani and his research partners discovered the well-preserved remains of a lizard-like aquatic reptile called a thalattosaur inside the stomach of Middle Triassic ichthyosaur. The fossil, described Thursday in the journal iScience, represents the oldest record of megafaunal predation by a marine reptile.
"We have to readjust our estimation of the prevalence of megapredators," Motani wrote. "It seems that megapredation was more common than previously thought."
Megapredation describes the hunting and eating of megafauna, animals that were bigger than humans.
Researchers spent several years visiting the quarry site in southwestern China where the thalattosaur and ichthyosaur remains were discovered. It took them awhile to believe what they were seeing.
Not only was the lizard-like reptile big, measuring more than 14 feet long, it was also remarkably well-preserved. That is showed no signs of disintegration from exposure to stomach acid suggests the ichthyosaur perished not long after eating the thalattosaur.
"Usually, stomach contents do not contain articulated remains because digestion breaks down the prey in the stomach," Motani wrote. "So, we do not expect to find such a fossil everyday, and it is surprising that we happened to find one."
Researchers can't be certain whether the ichthyosaur scavenged the giant reptile or hunted and killed it, but the lizard-like specimen's tail was found separated from its body, several feet away, suggesting a tussle between predator and prey.
The mass extinction at the end of the Permian greatly diminished the biodiversity found in Earth's oceans, but the latest discovery suggests marine ecosystems had rebounded by the Middle Triassic.
It seems that once the ecosystem was healthy enough to support large predators in the Middle Triassic, multiple lineages took the opportunity and engaged in megapredation almost simultaneously," Motani said.
There are more fossils at the Chinese quarry site, and researchers plan to continue studying them in an effort to answer lingering questions about Mesozoic life, such as the precise timing of open-sea colonization by reptiles.