Large aquatic reptiles known as ichthyosaurs appeared in the oceans about 250 million years ago after the Permian mass extinction. These reptiles looked like fish but breathed air like dolphins and whales.
While scientists have theorized that ichthyosaurs were top predators in their ocean ecosystems like killer whales or great white sharks, there has been little direct evidence to support this theory.
But now, in a new study from UC Davis, scientists are describing the fossilized remains of a five-meter ichthyosaur that swallowed a four-meter reptile just before its death.
The 240 million-year-old remains of the ichthyosaur Guizhouichthyosaurus were discovered in 2010 in Guizhou province, China.
The fossils represent the earliest evidence of a large animal preying on another large animal, or megapredation.
“We have never found articulated remains of a large reptile in the stomach of gigantic predators from the age of dinosaurs, such as marine reptiles and dinosaurs,” said study co-author Professor Ryosuke Motani. “We always guessed from tooth shape and jaw design that these predators must have fed on large prey but now we have direct evidence that they did.”
When the fossil skeleton was first uncovered, researchers noticed a large bulge of other bones within the animal’s abdomen. Upon further analysis, they identified the smaller marine reptile as a thalattosaur called Xinpusaurus xingyiensis, which was lizard-like in appearance with four paddling limbs.
The predator’s last meal appears to be the middle section of the thalattosaur, from its front to back limbs. The bones of what appears to be the tail section of the prey were found nearby.
“Guizhouichthyosaurus is a genus of ichthyosaur that would not be considered an apex predator based on the traditional criteria,” wrote the study authors. They explained that its typical size range is about four to six meters in total length, although some individuals reached about 7 meters. “Its teeth lacked carinae and were not very large for the body size.”
Guizhouichthyosaurus had small, peg-like teeth that appeared to be better adapted for handling squid-like animals that were abundant in the oceans at the time. However, it’s clear that you don’t need slicing teeth to be a megapredator, said Professor Motani.
Guizhouichthyosaurus likely used a strategy that is similar to that of modern crocodiles and orca – using the force of its bite to injure the prey before ripping it apart.
The study is published in the journal iScience.