Fossils provide critical insights into the ancient world and the interactions of various species that lived there. Such discoveries can help us better understand the ecological dynamics of past ecosystems by shedding new light on the behaviors and interactions of prehistoric creatures.
An unusual fossil discovered in China around 125 million years ago depicts a dramatic moment in time when a carnivorous mammal attacked a larger plant-eating dinosaur. The two animals are engaged in mortal combat, and this is one of the first examples of predatory behavior by a mammal on a dinosaur. The presence of the fossil calls into question the belief that dinosaurs faced few threats from their mammalian contemporaries during the Cretaceous period, when dinosaurs were the dominant animals.
Canadian and Chinese scientists have described an unusual fossil from around 125 million years ago that depicts a dramatic moment in time when a carnivorous mammal attacked a larger plant-eating dinosaur.
“The two animals are locked in mortal combat, intimately intertwined, and it’s among the first evidence to show actual predatory behavior by a mammal on a dinosaur,” explains Dr. Jordan Mallon, palaeobiologist with the Canadian Museum of Nature and co-author on the study published today in the journal Scientific Reports.
The two animals are locked in mortal combat, intimately intertwined, and it’s among the first evidence to show actual predatory behavior by a mammal on a dinosaur.
Dr. Jordan Mallon
The presence of the fossil calls into question the belief that dinosaurs faced few threats from their mammalian contemporaries during the Cretaceous period, when dinosaurs were the dominant animals. The rare fossil is now housed in the Weihai Ziguang Shi Yan School Museum in Shandong Province, China.
The dinosaur in the well-preserved fossil has been identified as a Psittacosaurus species, which is roughly the size of a large dog. Plant-eating psittacosaurs, which lived in Asia between 125 and 105 million years ago, are among the earliest known horned dinosaurs. Repenomamus robustus, a badger-like animal, is the mammal in the fossil pair. Although not large by dinosaur standards, it was among the largest mammals during the Cretaceous, at a time when mammals had not yet come to dominate the Earth.
Prior to this discovery, palaeontologists knew that Repenomamus preyed on dinosaurs including Psittacosaurus because of fossilized baby bones of the herbivore found in the mammal’s stomach.
“The co-existence of these two animals is not new, but what’s new to science through this amazing fossil is the predatory behaviour it shows,” says Mallon.
The fossil was discovered in Liaoning Province, China, in 2012, and both skeletons are nearly complete. Their completeness is due to their origin in the Liujitun fossil beds, which have been dubbed “China’s Dinosaur Pompeii.”
The name refers to the numerous dinosaur, small mammal, lizard, and amphibian fossils found in the area, animals that were buried suddenly en masse by mudslides and debris following one or more volcanic eruptions. Dr. Aaron Lussier, a mineralogist at the Canadian Museum of Nature, confirmed the presence of volcanic material in the rock matrix of the study’s fossil.
The Psittacosaurus-Repenomamus fossil was in the care of study co-author Dr. Gang Han in China, who brought it to the attention of Canadian Museum of Nature palaeobiologist Xiao-Chun Wu. Dr. Wu has worked with researchers in China for decades and knew it was special when he saw it.
The Psittacosaurus is lying prone, with its hindlimbs folded on either side of its body, according to a close examination of the fossil pair. The Repenomamus’s body coils to the right and sits atop its prey, the mammal gripping the larger dinosaur’s jaw. The mammal is also biting into some of the ribs, and Repenomamus’ back foot is gripping the dinosaur’s hind leg. “The weight of the evidence suggests that an active attack was underway,” says Dr. Mallon.
Mallon, Wu, and colleagues ruled out the possibility that the mammal was simply scavenging the carcass of a dead dinosaur. The dinosaur’s bones, for example, lack tooth marks, indicating that it was preyed on rather than scavenged. And it’s unlikely the two animals would have become so entangled if the dinosaur had been dead before the mammal came upon it. The position of the Repenomamus over top of the Psittacosaurus suggests it was also the aggressor.
In the modern world, there are analogies of smaller animals attacking larger prey. Mallon and Wu point out that lone wolverines have been observed hunting larger animals such as caribou and domestic sheep. On the African savanna, wild dogs, jackals, and hyenas will attack still-alive prey, resulting in the prey collapsing, often in shock.
“This could be the case depicted in the fossil, with the Repenomamus eating the Psittacosaurus while it was still alive – before both were killed in the roily aftermath,” Mallon explains.
The research team speculates in their paper that the volcanically derived deposits from the Lujiatun fossil beds in China will continue to yield new evidence of interactions among species, otherwise unknown from the rest of the fossil record.
