While many Mesozoic mammals undoubtedly became food for a dinosaur, it may be surprising 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 herbivorous dinosaur about 125 million years ago and sinking its teeth into its prey’s ribs, scientists said Tuesday.
Dating to the Cretaceous period, it shows the four-legged mammal Ripenomamus robustus – the size of a domestic cat – brutally entangled with the beaked biped Psittacosaurus lugiatunensis – as large as a medium-sized dog. Scientists suspect that they were suddenly submerged in a volcanic mudflow during the deadly struggle and buried alive.
“Dinosaurs almost always outcompeted their mammalian contemporaries, so the traditional belief was that their interactions were one-sided — the bigger dinosaurs always ate the smaller mammals,” said paleobiologist Jordan Mallon of the Canadian Museum of Nature in Ottawa.
“Here, we have good evidence of a small mammal preying on a large dinosaur, something we wouldn’t have guessed without this fossil,” Mallon added.
Most mammals of the Mesozoic Era, the age of the dinosaurs, were shrew-sized bit players in the grand theater of life, doing well to avoid being someone else’s lunch. Repenomamus shows that at least some mammals gave as good as they got.
“I think the key here is that Mesozoic food webs were more complex than we thought,” Mallon said.
The area in Liaoning Province where the virtually complete fossils were found has been called the “Chinese Pompeii” because of the variety of animal fossils buried in volcanic eruptions.
Examining the fossil was like analyzing a crime scene. Ripenomamus is likely above Psittacosaurus, holding its jaws and hind legs while biting its ribs. Repenomamus measures 1-1/2 feet (47 cm) in length. Psittacosaurus was 4 feet (120 cm) long. Both are believed to be minors.
“There have been previous examples of carnivorous dinosaurs preying on herbivorous dinosaurs, but there has never been an example of a mammal preying on a dinosaur,” said Xiao-Chun Wu, a Canadian Museum of Nature paleontologist and study co-author.
Finding fossils that show animals interacting is rare. Another fossil discovered in Mongolia in the 1970s shows two dinosaurs — the predator Velociraptor and the plant-eater Protoceratops — fought about 80 million years ago, possibly on a collapsed sand dune.
The researchers rejected the idea that the fossils of Repenomamus and Psittacosaurus showed a mammal simply scavenging a carcass.
“One, the mammal is on top of the dinosaur trying to subdue it, which doesn’t account for the scavenger theory,” Mallon said.
“Secondly, there are no bite marks on the dinosaur bones, which we would expect if scavengers had been sitting outdoors for long periods of time. “Finally, the mammal’s hind legs got caught in the dinosaur’s folded back leg, which is unlikely to have happened if the dinosaur was dead when the mammal tackled it,” Mallon added.
Psittacosaurus was an early relative of the horned dinosaur family, lacking facial horns and head crests. It had a parrot-like beak for harvesting plants.
One of the largest mammals of the dinosaur era, Repenomamus had short, flat limbs, a long tail, a sinuous body, a robust skull, and scissor teeth. Mallon compared its appearance to a living Chinese ferret-badger.
There was earlier evidence for the dino-eating habits of Ripenomamus. A Repenomamus fossil from the same area contained baby Psittacosaurus bones in its stomach.
“Our fossil is unique in that it demonstrates that Repenomamus was able to take on large dinosaur prey,” Mallon said.