Dinosaurs are often painted as predators, chasing down everything from smaller dinosaurs to Jeff Goldblum, but we often overlook their role as prey. Many dinosaurs were dinner for bigger dinosaurs, but as a fascinating new fossil reveals, some were lunch for early mammals, too.
The unusual and rare fossil is 125 million years old and shows two animals locked in mortal combat as a carnivorous mammal attacked a larger plant-eating dinosaur. According to co-author on a new study, Dr Jordan Mallon, who is a palaeobiologist with the Canadian Museum of Nature, it’s among the first pieces of evidence to show a mammal predating on a dinosaur, rather than the other way around.
“I think what’s most interesting is the fact that this new fossil shows that ecological interactions between dinosaurs and mammals went both ways; it wasn’t just the larger dinosaurs eating the smaller mammals,” Mallon said to IFLScience. “Sometimes, mammals were capable of eating dinosaurs – even nearly fully grown ones – too.”
The dinosaur being preyed on is a species of Psittacosaurus, a group of plant-eating dinosaurs that became the proud owners of the first known fossilized butt orifice back in 2021. In life, they were about the size of a large dog, which doesn’t sound all that impressive until you learn that the mammalian species hunting it, Repenomamus robustus, was only the size of a badger. Pretty mini compared to the biggest mammals alive today, but it was one of the largest alive during the Cretaceous when mammals hadn’t yet dominated the landscape.
We were curious to know how the teeth of a badger-like animal would fare against the hide of a Psittacosaurus, something you might imagine to be a bit leathery. However, as Mallon explained, they probably weren’t too tough a menu item.
“Interesting question! Although we have found skin impressions from Psittacosaurus before, we don’t have any sense for how thick the skin was. This was a relatively small dinosaur, so I don’t think it would have been particularly thick-skinned in the way that today’s large elephants or hippopotamus are. Repenomamus was a known carnivore, so I think it was certainly capable of tearing through flesh – even that of dinosaurs.”
The curious fossil was retrieved from China's Liaoning Province in 2012, from an area nicknamed “China’s Dinosaur Pompeii”. Both skeletons are nearly complete and come from an area known as the Liujitun fossil beds where many fossils of dinosaurs, small mammals, lizards, and amphibians were buried after volcanic eruptions unleashed mudslides and deluges of debris.
We can see this in the volcanic material that was found in the rock matrix of the study’s fossil, as confirmed by mineralogist Dr Aaron Lussier at the Canadian Museum of Nature. It might sound like something of a fluke to capture a moment like this in the fossil record, but it’s not alone.
“To preserve an interaction like this one, it’s necessary to bury the individuals quickly,” said Mallon. “In the case of the animals described in our study, they were buried by a swift mudslide consisting mostly of volcanic ash and debris. There’s [also] a famous pair of 'fighting dinosaurs' from the Gobi desert that were buried suddenly in a dune collapse.”
If only Repenomamus robustus had known, it pays to keep one eye on the horizon while you tuck into a dinosaur.
The study is published in Scientific Reports.