Mammal dinosaur fossil

New fossil discovery supports an idea first proposed in 2005: the early Cretaceous mammals weren’t just shrinking violets, tiny earthworms hiding in the dinosaurs’ shadows. According to the new thinking, some of the mammals were predators in their own right, attacking and eating small dinosaurs and their young.

The Ferocious Prehistoric Predator: A Badger-like Dinosaur Killer , The new fossil from China shows a small, badger-like carnivore, a Repenomamus robustuson top of a Psittacosaurus, a beaked herbivorous dinosaur the size of a large dog. The mammal clutches the dinosaur with its left paw as it twists to the right and bites the reptile’s ribs in a dramatic embrace. It’s so dramatic, in fact, that researchers say the dinosaur was probably alive at the time and not yet dead.

“The weight of evidence suggests that an active attack was underway,” said Jordan Mallon, a paleobiologist at the Canadian Museum of Nature, in declaration.

Diorama of Death

Both skeletons that make up the fossil are in remarkable shape and are nearly complete. Scientists assembled the dramatic scene, a diorama of death, from China’s Liaoning Province in 2012 from the country’s “Dinosaur Pompeii.” The area contains many dinosaurs, small mammals, lizards and amphibians, buried by mudslides and other debris that fell during volcanic eruptions.

“The coexistence of these two animals is not new, but what is new to science through this amazing fossil is the predatory behavior it exhibits,” says Mallon.

The fossil came to light when one of the co-authors, paleontologist Gang Han of China, sent it to Xiao-Chun Wu, a paleobiologist at the Canadian Museum of Nature. They assembled a team of Canadian and Chinese scientists who dated the bones to 125 million years ago, when dinosaurs dominated the earth.

An artist recreating the fateful encounter. (Credit: Michael Skrepnik)

Did mammals compete with dinosaurs?

In 2005paleontologists reported the discovery of an R. robustus fossil that contained the bones of a baby dinosaur, shaking up old assumptions about early mammals. The minor Psittacosaurus measuring about 5 inches and appeared to have been dismembered and swallowed quickly. Like the later fossils, they come from northeastern China and date to about the same time, 130 million years ago.

An even more dangerous kind of Repenomamus walked the same earth as the dinosaurs. The size of a coyote R. giganticus “probably competed with carnivorous dinosaurs for food and territory,” researcher Yaoming Hu said Science.

Modern analogies abound of small predators attacking larger prey, from wolverines fighting sheep to coyotes killing deer and even buffalo. There are also analogies of predators eating their prey while they are still alive, which the researchers say is preserved in the new fossil.

“This may be the case with the one depicted,” says Mallon, “with Repenomamus actually eat Psittacosaurus while it was still alive—before they were both killed in the terrible aftermath.”

Read more: Did humans and dinosaurs ever live together?

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