Fossil shows carnivorous mammal attacking dinosaur

In an extraordinary discovery, scientists from Canada and China have unveiled a rare fossil dating back around 125 million years, capturing a remarkable and intense moment in prehistoric history. This unique finding provides evidence of a dramatic encounter between a carnivorous mammal and a larger, plant-eating dinosaur.

Dr. Jordan Mallon, a paleobiologist associated with the Canadian Museum of Nature and a co-author of the study published in Scientific Reports, explains that the fossil displays a captivating scene of these ancient adversaries locked in mortal combat. This find sheds light on the predatory behavior of mammals towards dinosaurs, challenging the prevailing notion that dinosaurs faced few threats from their mammalian counterparts during the Cretaceous period when they dominated the Earth.

Currently housed in the Weihai Ziguang Shi Yan School Museum in China’s Shandong Province, this well-preserved fossil showcases a Psittacosaurus, a horned dinosaur species about the size of a large dog. These herbivorous creatures inhabited Asia during the Early Cretaceous period, spanning from approximately 125 to 105 million years ago. The other participant in this ancient struggle is a Repenomamus robustus, resembling a badger-like mammal. While not massive by dinosaur standards, during the Cretaceous era, it ranked among the largest mammals, predating the time when mammals later rose to dominance on Earth.

Fossil showing the entangled skeletons of Psittacosaurus (dinosaur) and Repenomamus (mammal), with magnified sections showing the mammal biting the dinosaur’s ribs, and gripping its prey. Scale bar equals 10 cm. Credit: Gang Han

Paleontologists had previous knowledge of Repenomamus preying on dinosaurs, particularly Psittacosaurus, thanks to the discovery of fossilized baby bones from the herbivore found inside the mammal’s stomach.

Dr. Jordan Mallon emphasizes that the coexistence of these two creatures was not a new revelation, but what makes this recent fossil truly remarkable is the concrete evidence it provides of predatory behavior.

The fossil was unearthed in China’s Liaoning Province back in 2012, and both skeletons are remarkably well-preserved. This exceptional preservation can be attributed to the site’s name, the Liujitun fossil beds, often referred to as “China’s Dinosaur Pompeii.” The name stems from the fact that the area contains a wealth of fossils, including dinosaurs, small mammals, lizards, and amphibians, all seemingly buried suddenly by mudslides and debris following volcanic eruptions. The presence of volcanic material in the fossil’s rock matrix was confirmed through analysis by Dr. Aaron Lussier, a mineralogist at the Canadian Museum of Nature.

Illustration showing Repenomamus robustus as it attacks Psittacosaurus lujiatunensis moments before a volcanic debris flow buries them both, ca. 125 million years ago. Credit: Michael Skrepnick
Life reconstruction showing Psittacosaurus (dinosaur) being attacked by Repenomamus (mammal), 125 million years ago. Credit: Michael Skrepnick

In the care of study co-author Dr. Gang Han in China, the Psittacosaurus-Repenomamus fossil caught the attention of Canadian Museum of Nature’s paleobiologist, Xiao-Chun Wu.

A meticulous examination of the fossilized pair reveals intriguing details of their final moments. The Psittacosaurus is found lying prone, its hindlimbs folded at the sides of its body. In a gripping display of predation, the Repenomamus coils to the right, firmly perched on top of its prey. The mammal clutches the jaw of the larger dinosaur while also biting into some of its ribs. Notably, the back foot of the Repenomamus clings onto the hind leg of the Psittacosaurus. Dr. Mallon emphasizes that the collective evidence strongly suggests an active attack was underway.

Through comprehensive analysis, Mallon, Wu, and their fellow researchers have ruled out the possibility that the mammal was merely scavenging a deceased dinosaur. Notably, the bones of the Psittacosaurus exhibit no tooth marks, signifying that it was not being scavenged. Instead, the evidence points to the dinosaur being preyed upon by the Repenomamus. Furthermore, it appears unlikely that the two creatures would have become so intricately intertwined if the Psittacosaurus had already been dead before the mammal encountered it. The positioning of the Repenomamus over the Psittacosaurus indicates that it was indeed the aggressor in this ancient encounter.

Detail of larger fossil, showing Repenomamus (mammal) biting the ribs of Psittacosaurus (dinosaur). Credit: Gang Han
Hillside where the fossil was collected from the Lujiatun Member of the Yixian Formation of northeastern China in 2012. Credit: Gang Han

In the modern world, we can find analogies of smaller animals fearlessly attacking larger prey, and this phenomenon is echoed in the findings of Mallon and Wu. For instance, lone wolverines have been observed hunting larger animals like caribou and domestic sheep, displaying remarkable tenacity in their pursuit. On the African savanna, wild dogs, jackals, and hyenas are known to launch attacks on live prey, causing their victims to collapse in a state of shock.

Drawing a parallel to the fossil discovery, Dr. Mallon suggests that the Repenomamus might have engaged in a similar behavior, devouring the Psittacosaurus while it was still alive. This leads to the intriguing possibility that both creatures met their fate during the tumultuous aftermath of the event that buried them together.

Looking to the future, the research team believes that the volcanic deposits in China’s Lujiatun fossil beds will continue to unveil more evidence of species interactions previously unknown to the scientific community. These remarkable findings have the potential to shed further light on the ancient world and its intricacies, contributing to a deeper understanding of prehistoric ecosystems and the dynamics between various species.

Source: Canadian Museum of Nature

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