Dramatic fossil shows mammal attacking dinosaur

An illustration of Repenomamus robustus, a mammal, attacking the plant-eating dinosaur Psittacosaurus lujiatunensis moments before a volcanic debris flow buried them both, about 125 million years ago in China.
| Photo Credit: Michael W. Skrepnick/Reuters

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 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 July 18.

Dated 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.

“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 palaeobiologist 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.

The area in Liaoning Province where the virtually complete fossil was found is called the “Chinese Pompeii” owing to various fossils of animals buried in volcanic eruptions.

Examining the fossil was like a crime scene analysis. Repenomamus is perched atop the prone Psittacosaurus, gripping the jaw and hind leg while biting into the ribcage. Repenomamus measures 47 cm long. Psittacosaurus is 120 cm long. Both are thought to be not quite full adults.

“There have been specimens of carnivorous dinosaurs preying on plant-eating dinosaurs before, but there has never been an example of a mammal preying on a dinosaur,” said Canadian Museum of Nature palaeontologist and study co-author Xiao-chun Wu.

It is rare to find fossils showing animals interacting. Another fossil found in the 1970s in Mongolia shows two dinosaurs, predator Velociraptor and plant-eater Protoceratops, fighting about 80 million years ago before being buried alive, perhaps in a collapsing sand dune.