While there is no doubt that many Mesozoic mammals became food for a dinosaur, it may come as a surprise to learn that some mammals also ate dinosaurs.
A dramatic fossil unearthed in northeast China shows a warlike badger-like mammal attacking a herbivorous dinosaur, mounting its prey and sinking its teeth into its victim’s ribs some 125 million years ago, scientists said Tuesday.
Dating to the Cretaceous period, it shows the four-legged mammal Repenomamus robustus, the size of a domestic cat, fiercely entangled with the two-legged beaked dinosaur Psittacosaurus lujiatunensis, the size of a medium-sized dog. Scientists suspect that they were suddenly engulfed in a volcanic mudflow and buried alive during mortal combat.
«Dinosaurs almost always outsized their mammalian contemporaries, so the traditional belief has been that their interactions were one-sided: the larger 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 of a smaller mammal feeding 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 the dinosaurs, were shrew-sized little players in the larger theater of life, doing well to avoid becoming someone else’s lunch. Repenomamus shows that at least some mammals did their best.
«I think the key here is that Mesozoic food webs were more complex than we had imagined,» Mallon said.
The area in Liaoning province where the nearly complete fossil was found is called the «Chinese Pompeii» because of various animal fossils buried in volcanic eruptions.
Examining the fossil was like a crime scene analysis. Repenomamus is perched on the upside-down Psittacosaurus, grasping the jaw and hind leg while biting down on the ribcage. Repenomamus is 1-1/2 feet long. The psittacosaurus is 4 feet long. It is believed that both are not fully complete adults.
«There have been specimens of carnivorous dinosaurs preying on herbivorous dinosaurs before, but there has never been an example of a mammal preying on a dinosaur,» said Xiao-chun Wu, a paleontologist at the Canadian Museum of Nature and a co-author of the study.
It is rare to find fossils that show animals interacting. Another fossil found in the 1970s in Mongolia shows two dinosaurs, the predatory Velociraptor and the herbivore Protoceratops, fighting around 80 million years ago before being buried alive, perhaps in a collapsing sand dune.
The researchers dismissed the idea that the Repenomamus and Psittacosaurus fossil showed a mammal simply rummaging through a carcass.
«For one thing, the mammal is on top of the dinosaur as if it’s trying to subdue it, which the scavenger hypothesis doesn’t account for,» Mallon said.
“Second, there are no bite marks on the dinosaur’s bones, which we would expect if it had been sitting around for a long time, exposed to scavengers. Ultimately, the mammal’s hind leg becomes trapped by the dinosaur’s bent hind leg, which is unlikely to have happened if the dinosaur had already been dead when the mammal encountered it,» Mallon added.
While Psittacosaurus was an early relative of the horned dinosaur lineage, it lacked facial horns and a head crest. It possessed a parrot beak for harvesting plant material.
Repenomamus, one of the largest mammals of the dinosaur age, had short, splayed limbs, a long tail, a sinuous body, a robust skull, and cutting teeth. Mallon compared its appearance to that of a living Chinese ferret badger.
There was previous evidence of Repenomamus dino eating habits. A Repenomamus fossil from the same area had baby Psittacosaurus bones in its stomach.
“What is unique about our fossil is the fact that it shows that Repenomamus was capable of taking on larger dinosaur prey,” Mallon said.