About 120 million years ago, in the early Cretaceous period, the Earth's jungles first began to burst with the colors of blooming flowers. As the remnants of the supercontinent Pangaea drifted towards their present locations, a diverse array of dinosaurs roamed these changing landscapes. Towering behemoths like Spinosaurus and the smaller, yet ferocious Utahraptor were among the era's dominant predators.
Contrasting these colossal beings, prehistoric mammals, mostly small and inconspicuous, lurked in the shadows, overlooked, and underestimated.
At least, that’s been paleontology’s long-held view of the ancient food web, until recently. A study by Canadian and Chinese scientists, focusing on a fossil discovered in China's Liaoning Province, has dramatically rewritten our understanding of what ancient mammals were capable of.
Rare Discovery of Repenomamus Fossil Engaged in Battle
The fossil, remarkably well-preserved, captured a moment of raw survival. It features Repenomamus robustus — an ancient mammal roughly the size of a modern badger, making it a giant among mammals of the time — engaged in an attack on a Psittacosaurus, a common herbivorous dinosaur of the era.
Since less than 0.1 percent of organisms fossilize, just discovering the two creatures together is a sheer miracle, let alone with them engaged in mortal combat. It appears the two creatures were engulfed in volcanic ash mid-battle, leaving them remarkably well preserved.
Could Mammals Attack Dinosaurs?
The discovery of this rare scene prompts a fascinating question: Just how common were these instances of role reversal between the massive reptiles and their smaller mammalian counterparts? To explore this, Jordan Mallon from the Canadian Museum of Nature in Ottawa teamed up with researchers from the Chinese Academy of Sciences to study the fossil in detail.
Mammals v. Dinosaurs: A Role Reversal in Prehistoric Food Chains?
“Dinosaurs nearly always outsized their mammal contemporaries, leading to the traditional belief that interactions were mainly one-sided, with the larger dinosaurs preying on the smaller mammals. This fossil, however, provides strong evidence to the contrary, showing a smaller mammal actively preying on a larger dinosaur — a scenario that, until now, we could hardly have imagined,” says Mallon.
How Did Repenomamus Hunt?
To understand how Repenomamus robustus might have hunted its larger dinosaur prey, we can look to modern analogs. In the frosty forests of Alaska and Canada, for instance, wolverines are known for their tenacity in hunting. Despite their size, comparable to a medium dog, they can ferociously take down much larger prey – like reindeer. They achieve this magnificent feat by leaping at the reindeer's neck, and clinging fiercely as they slash and gnaw. It's feasible that R. robustus could have used a similar strategy.
“Whether Repenomamus employed the same hunting strategy as the wolverine is difficult to say, but I wouldn’t be surprised if it did. Given that Psittacosaurus was an abundant prey item in its environment, Repenomamus would have needed to be quite aggressive to take one down,” says Mallon.
The Predatory Mammals Role in Population Control
Predators like wolverines play a crucial role in keeping herbivores from reaching their carrying capacity, which is the number of individuals an environment can support without exploitation of resources and environmental degradation. Scientists like Mallon want to investigate whether prehistoric mammals like R. robustus could have played a similar role in keeping some dinosaur species at their carrying capacity.
“We know that predation pressure today can strongly impact the population growth of small herbivores, and I wonder if the same was true during the Mesozoic. Those answers are hard to get at, though,” says Mallon.
Were the Repenomamus Fossils Real?
The fossil shook science's understanding of the Mesozoic food web, to such a degree that Mallon was initially skeptical that the fossil was legitimate. It is unfortunately common for fossils to be “enhanced” or even entirely fabricated in fossil rich regions, by individuals seeking to make a profit from selling them to both private and public collections. Some common methods of fabrication include using plaster and resin to mold fake fossils, or even merging existing fossils to create something potentially more visually appealing.
A notorious case of the latter being the infamous “Archaeoraptor” – a widely publicized fossil, hailed by National Geographic as the missing link between birds and dinosaurs. The fossil was later discovered to be a fake composed of as many as five separate specimens and is regarded as the biggest hoax fossil of all time.
How Scientists Analyzed the Badger-Like Fossils
However, through using techniques such as CT scans, chemical tests, and microscopic analysis, it’s possible to identify fakes. Thankfully, Mallon and his fellow researchers could authenticate their fossils.
“Fossil finds showing mammals preying on dinosaurs are significant in that they represent a piece of the ecological puzzle that we didn’t have before,” says Mallon.
R. robustus is a wake-up call in a sense, proving that in paleontology – and indeed in every realm of science, we can’t lean too heavily on our assumptions.
“That’s a lesson that we’re doomed to learn over and over again in paleontology, and I’m okay with that. Part of the fun of science is being surprised, occasionally,” says Mallon.