Dramatic fossil shows pugnacious mammal attacking a dinosaur

Mammal Repenomamus robustus preys on dinosaur Psittacosaurus lujiatunensis, 125 million yrs ago, in China. Fossil shows mammal atop dinosaur, gripping jaw & hind leg while biting ribcage.

While there is little doubt that many a Mesozoic mammal became a meal for a dinosaur, it may come as a surprise to learn that some mammals also dined on dinos.

A dramatic fossil unearthed in northeastern China shows a pugnacious badger-like mammal in the act of attacking a plant-eating dinosaur, mounting its prey and sinking its teeth into its victim’s ribs about 125 million years ago, scientists said on Tuesday.

Dating to the Cretaceous Period, it shows the four-legged mammal Repenomamus robustus - the size of a domestic cat - ferociously entangled with the beaked two-legged dinosaur Psittacosaurus lujiatunensis - as big as a medium-sized dog. The scientists suspect they were suddenly engulfed in a volcanic mudflow and buried alive during mortal combat.

“Dinosaurs nearly always outsized their mammal contemporaries, so traditional belief has been that their interactions were unilateral - the bigger dinosaurs always ate the smaller mammals,” said paleobiologist Jordan Mallon of the Canadian Museum of Nature in Ottawa, who helped lead the study published in the journal Scientific Reports.

“Here, we have good evidence for a smaller mammal preying on a larger dinosaur, which is not something we would have guessed without this fossil,” Mallon added.

Most mammals during the Mesozoic Era, the age of dinosaurs, were shrew-sized bit players in the larger theater of life, doing well to avoid becoming someone else’s lunch. Repenomamus shows at least some mammals gave as good as they got.

“I think what’s key here is that Mesozoic food webs were more complex than we had imagined,” Mallon said.