The predatory mammal had just bitten into its dinosaur victim when the duo was transformed into a time capsule by a flow of volcanic material: This is how paleontologists explain the formation of an exciting double fossil from the Cretaceous period. According to them, this is new evidence that some mammals of the dinosaur era also preyed on small representatives of the animal group that was dominant at the time.
They initially led a shadowy existence, it is said: although the evolutionary history of mammals dates back to the Triassic era, the evolutionary career of our ancestors could only really unfold after the asteroid impact at the end of the Cretaceous period had eliminated the dinosaurs. For a long time it was also assumed that the comparatively small predatory mammals of the Mesozoic era only preyed on insects and were more likely to fall prey to dinosaurs themselves.
But then finds showed that this was at least not entirely the case: Bones of psittacosaurs were found in the abdomen of a Cretaceous fossil of the badger-like Repenomamus robustus. They have already shown that at least young animals of these roughly dog-sized herbivores were on the predatory mammal's menu. As an international team of paleontologists led by Gang Han from China's Hainan Vocational University of Science and Technology now reports, their study now expands the picture of this special predator-prey relationship.
A find from the "Dinosaur Pompeii"
The double fossil that the paleontologists are now presenting comes from a site in Liaoning Province that has been dubbed the "Dinosaur Pompeii of China." Cretaceous animals were once caught there by volcanic mud or ash flows and suddenly preserved - similar to people in the ancient city of Pompeii. The investigations of the approximately 125 million year old complex fossil showed that it consists of the detailed remains of a Repenomamus robustus around 50 centimeters tall and a 120 centimeter long Psittacosaurus lujiatunensis.
As the team reports, closer examination revealed that the animals were preserved together in a striking constellation: the psittacosaurus appeared to be lying on its stomach while the repenomamus crouched on top of it in a hunched position. The mammal had apparently bitten into the side of the dinosaur, while one paw was on the neck area and a rear one was also clinging to the animal. "Combined, the findings suggest that an attack was underway," says co-author Jordan Mallon of the Canadian Museum of Nature in Ottawa. Analysis of the rock in which the animals were embedded confirmed that the predatory scene was actually suddenly preserved by a material flow: the researchers found typical volcanic components in it.
A predator-prey scenario is emerging
According to the researchers, it seems less likely that the mammal was working on an animal that was already dead. Because, in addition to the clues from the physical positioning, the bones of the dinosaur do not show any tooth marks, as would be typical for a gnawed carcass. The researchers emphasize that the difference in size between the two animals also fits into the picture. According to them, analogies are known from today's animal world: for example, the badger-like wolverines capture the much larger caribou by biting into them.
Mallon is convinced: “The two animals were involved in a deadly fight when fate overtook them. This is an indication of the predatory behavior of a mammal towards a dinosaur," says the paleontologist. "The fossil thus challenges the common assumption that Mesozoic mammals were merely food for the dominant dinosaurs," the scientists write. The team is now hoping for more finds from the "Chinese dinosaur Pompeii" that also "tell" about interactions between the animals of the dinosaur era.
Source: Canadian Museum of Nature, Article: Scientific Reports, doi: 10.1038/s41598-023-37545-8