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Odd Fossil Presentations Mammal Attacking a Dinosaur

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Fossil Entangled Skeletons Dinosaur and Mammal

Fossil appearing the entangled skeletons of Psittacosaurus (dinosaur) and Repenomamus (mammal) and their interplay simply prior to dying. NOTE: The dimensions bar equals 10 cm. Credit score: Gang Han

A 125-million-year-old fossil, appearing a carnivorous mammal attacking a dinosaur, demanding situations the long-standing trust that Cretaceous dinosaurs faced minimal threats from mammals. This significant finding offers new insights into prehistoric predator-prey dynamics.

A Glimpse into Prehistoric Predation

Canadian and Chinese scientists have unearthed an unusual fossil, dating back roughly 125 million years, that depicts a carnivorous mammal attacking a larger plant-eating dinosaur. This remarkable find offers a snapshot of a dramatic moment frozen in time.

Dinosaur Mammal Encounter Illustration

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

“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 on July 18 in the journal Scientific Reports.

The fossil’s presence challenges the conventional view that dinosaurs had few threats from their mammal contemporaries during the Cretaceous, when dinosaurs dominated. The unique fossil is now housed in the collections of the Weihai Ziguang Shi Yan School Museum in China’s Shandong Province.

Mammal Biting Dinosaur Fossil

Detail of larger fossil, showing Repenomamus (mammal) biting the ribs of Psittacosaurus (dinosaur). Credit: Gang Han

Details of the Fossil Find

The fossil captures a carnivorous, badger-like mammal, called Repenomamus robustus, in the act of attacking a Psittacosaurus, a dinosaur about the size of a large dog. Psittacosaurs, which lived in Asia during the Early Cretaceous period from about 125 to 105 million years ago, are among the earliest known horned dinosaurs. Although not large by dinosaur standards, Repenomamus robustus was one of the biggest mammals of the Cretaceous period—a time when mammals had not yet achieved global dominance.

Prior to this discovery, it was known that Repenomamus preyed on dinosaurs including Psittacosaurus, due to the presence of fossilized baby dinosaur bones 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 behavior it shows,” says Mallon.

Dinosaur Mammal Encounter

Life reconstruction showing Psittacosaurus (dinosaur) being attacked by Repenomamus (mammal), 125 million years ago. Credit: Michael Skrepnick

Unearthing the Evidence

The fossil, collected in China’s Liaoning Province in 2012, is remarkably well-preserved with nearly complete skeletons of both animals. This level of preservation is due to its origin in the Liujitun fossil beds, an area aptly dubbed “China’s Dinosaur Pompeii.”

This name references the multitude of preserved fossils of dinosaurs, small mammals, lizards, and amphibians in the area—creatures that were rapidly buried by mudslides and debris from volcanic eruptions. Canadian Museum of Nature mineralogist Dr. Aaron Lussier confirmed the presence of volcanic material in the rock matrix of the fossil under study.

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.

Entangled Skeletons Dinosaur and Mammal Fossil Details

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

Analysis of the Predation Scene

Upon close examination, the fossil pair shows the Psittacosaurus lying prone, its hindlimbs folded on either side of its body. The Repenomamus is seen coiling to the right and sitting atop its prey, gripping the jaw of the larger dinosaur and biting into its ribs. The mammal’s back foot is also gripping onto the dinosaur’s hind leg. “The weight of the evidence suggests that an active attack was underway,” says Dr. Mallon.

The research team, including Mallon and Wu, dismissed the idea that the mammal was merely scavenging a dead dinosaur. The absence of tooth marks on the dinosaur’s bones, for example, suggests it was not being scavenged, but actively preyed upon. It is unlikely that the two animals would have become so entangled if the dinosaur had already been dead before the mammal found it. The position of the Repenomamus on top of the Psittacosaurus also suggests it was the aggressor.

Lujiatun Member of Yixian Formation

Hillside where the fossil was collected from the Lujiatun Member of the Yixian Formation of northeastern China in 2012. Credit: Gang Han

Modern Analogies and Future Discoveries

Similar situations of smaller animals attacking larger prey are observed in the modern world. For instance, lone wolverines are known to hunt larger animals like caribou and domestic sheep. In the African savanna, wild dogs, jackals, and hyenas will attack prey that is still alive, often leaving them in a state of shock.

“This might be the case of what’s depicted in the fossil, with the Repenomamus actually eating the Psittacosaurus while it was still alive—before both were killed in the roily aftermath,” explains Mallon.

The research team anticipates that the volcanically derived deposits from the Lujiatun fossil beds in China will continue to provide fresh evidence of interspecies interactions, hitherto unknown from the fossil record.

Reference: “An extraordinary fossil captures the struggle for existence during the Mesozoic” by Gang Han, Jordan C. Mallon, Aaron J. Lussier, Xiao-Chun Wu, Robert Mitchell and Ling-Ji Li, 18 July 2023, Scientific Reports.
DOI: 10.1038/s41598-023-37545-8



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