A paleontologist’s job is often like solving a puzzle with no picture on the box and most of the pieces missing. From scattered bones and teeth, scientists who study fossils extrapolate entire long-dead creatures and even relationships between different species. But every now and then, researchers get a windfall in the form of nearly complete skeletons, their bodies preserved in a way that offers a glimpse into their behavior in life.
This could be the case with a newly described fossil of a badger-like mammal and a Labrador retriever-sized dinosaur locked in what appears to be an eternal brawl. A mixed team of Canadian and Chinese researchers published their findings in the journal Scientific Reports on Tuesday, along with a section of the study devoted to addressing concerns that the fossil is a fake.
The prehistoric skirmish took place about 125 million years ago, in what is now northeastern China, and appears to be something like a man-bite-dog story from the age of the dinosaurs. Typically at that time, conventional wisdom holds, mammals were tame, leading a tenuous existence while fearsome reptiles shook the ground around them. But the unlikely fossil depicts a fight between a mammal called Repenomamus robustus and a bipedal, plant-eating relative of Triceratops called Psittacosaurus lujiatunensis.
Size-wise, the dinosaur had an advantage, but Repenomamus, preserved with its teeth embedded in the ribcage of Psittacosaurus, appears to have outweighed its weight. The dinosaur’s bones show no evidence of having been gnawed by scavengers, indicating that the Repenomamus encounter occurred when Psittacosaurus was still alive.
« Today, there are examples of small carnivorous mammals taking down much, much larger prey, » said Jordan Mallon, a paleontologist at the Canadian Museum of Nature and co-author of the study. He pointed to the wolverines culling caribou. He added: « We think Repenomamus was probably similarly a small, feisty predator that was willing to take down prey that was much larger than itself if necessary. »
Keeping the animals in the fray required a lot of luck (or bad luck, from the animals’ point of view). It started with a volcanic eruption, releasing ash. That ash may have been turned into a mudflow by seasonal flooding or heavy rain. So while this Repenomamus and Psittacosaurus were fighting, « this mudflow caught them off guard and preserved them for 125 million years, » Dr. Mallon said.
The fossil was unearthed in 2012 by farmers in China’s Liaoning province and acquired by Gang Han of the Hainan Vocational University of Science and Technology, co-author of the study. The discovery was incredible and there are numerous instances where such discoveries turned out to be too good to be true. False fossils, including separate specimens strung together to complete a skeleton or scene, are « a big problem, » Dr. Mallon said. « This was a concern we had, and so we had to do our homework to at least convince ourselves » that it was legitimate.
Dr Mallon said the researchers dug into the rock surrounding the fossils and found that the mammal’s lower left jaw was ‘really plummeting into the rock and really biting into the dinosaur’s ribs’, rather than just being put together by a fossil forger. . The researchers also analyzed the rock in the fossil and the rock from the fossil beds where it was presumably found; they matched. Based on these independent lines of evidence, « we feel quite satisfied that this is a real fossil and not a fake, » said Dr. Mallon.
Or if it’s a fake, he said, it’s « the best I’ve ever seen. »
David Grossnickle, an evolutionary biologist at the University of Washington who was also not involved in the study, said that while in the « worst-case scenario, » parts of the fossil specimen could have been forged, the skull of the mammal biting into the bone of the dinosaur appears to be real, and that piece alone is « still an amazing fossil. »
If no convincing challenge to its authenticity is presented, the fossil offers tantalizing evidence of how mammals and dinosaurs interacted.
« We rely on spectacular fossils like this one to really fill in the gaps in how these ancient ecosystems function, because we can’t always rely on bones alone to tell us these stories, » Dr Mallon said.
Michael Pittman, a paleontologist at the Chinese University of Hong Kong who was not involved in the study, said the immortalized bite didn’t necessarily mean Repenomamus was hunting dinosaurs for food and the animals may have been less involved. than a predator takedown and more than a « fight ».
But the study could contribute to « growing evidence that Mesozoic mammals were more ecologically diverse than classically thought, » Dr. Grossnickle said, « and get some revenge, I guess, on those big bad dinosaurs. »