For more than 230 million years, dinosaurs and mammals have coexisted on Earth, shaping evolution and leaving a profound impact on the planet’s biodiversity. Although both groups have flourished throughout history, direct evidence of their interactions is rare, making fossil finds that shed light on their ancient interactions all the more extraordinary. than.
In a groundbreaking discovery that has captured the attention of paleontologists worldwide, a new fossil from Member Lujiatun of the Lower Cretaceous Yixian Formation of China has revealed a Unique look into the past. The fossil, designated WZSSM VF000011, presents an extremely rare scene of entwined skeletons, depicting the fierce struggle between a gobiconodontid mammal and a psittacosaurid dinosaur.
The Lujiatun member of the Yixian Formation is well known for its abundance of vertebrate fossils, especially Psittacosaurus lujiatunensis, a small ceratopsian dinosaur that makes up nearly 90% of the local fossil assemblage. The site discovered near the village of Lujiatun in Liaoning province has provided invaluable insights into the ancient ecology that thrived in the Early Cretaceous.
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The dinosaur’s skeleton was complete, allowing paleontologists to confidently identify it as Psittacosaurus Lujiatunensis. Key diagnostic features, such as the width of the anterior frontal bone relative to the nasal bone and the contact between the quadrangular and squamous bones along the anterior margin of the quadrangular axis, confirm its identity. The dinosaur’s body position in the fossil shows that it was lying on its stomach, with its hind limbs folded to the sides of its body, while its neck and tail curved to the left.
The skeleton of this mammal is also very well preserved, although the end of the tail is missing. The preservation of important parts of the skeleton, such as the lower jaw and teeth, allowed experts to identify it as Repenomamus robustus. Although the teeth and mandibular features of this mammal are not entirely seen in the fossil record, its small size and unique features, such as the lance-shaped crest and crest weak pointed nose and zygomatic arch, clearly indicating that it was R. robustus and not the larger R. Giganticus.
The most striking aspect of the fossil is the intimate entanglement of the two individuals. The mammal’s left hand grips the dinosaur’s lower jaw, and its left hind leg is caught in the dinosaur’s folded left leg, with the hind foot gripping the dinosaur’s shin just below. knee. This mammal’s bite is centered on the dinosaur’s left front two ribs, which appear to have been broken, indicating a powerful and fatal attack.
The mammal’s positioning and grasping behavior suggests that it was the aggressor in this ancient battle, while the dinosaurs appear to be on the defensive, trying to dodge the attack. This interpretation is consistent with previous research showing that Repenomamus robustus was a carnivorous mammal capable of hunting smaller animals.
The role of volcanic debris flows in fossil conservation
The scientific team that conducted the study confirmed that the two animals died in a conflict, trapped by the volcanic mud that buried them. Since Psittacosaurus showed no signs of bite elsewhere, the researchers firmly concluded that the mammal was actively hunting a living dinosaur rather than scavenging.
Another and more convincing explanation is that this mammal actively hunted down the weakened dinosaur when both were buried. The mammal’s position atop the dinosaur, gripping its lower jaw and biting its ribs, suggests a predatory attempt rather than scavenging behavior. The sudden flow of volcanic debris may have interrupted this fateful encounter, preserving it for millions of years and providing scientists with a unique window into this ancient playbook.
The preservation and importance of the fossil stems from the characteristics of the bedrock where it was found. Analysis of the sedimentary material revealed it to be a matrix-supported, medium-hard tuff rock, indicating a volcanic origin and the presence of a volcanic debris stream. This lahar-type volcanic debris flow event occurred suddenly and violently, likely resulted in the two warriors being buried, and played an important role in preserving this ancient battle scene.
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Compare two species
The two entangled individuals in the fossil are a small dinosaur, Psittacosaurus lujiatunensis, and an even smaller mammal, Repenomamus robustus. Psittacosaurus was a relatively small ceratopsian dinosaur, known for its beak-like mouth and leaf-shaped cheek teeth, indicative of a herbivorous diet. Repenomamus, on the other hand, is a mammal of the gobiconodontid family, a group of early mammals with a mixture of reptilian and mammalian features.
Another intriguing aspect of the fossil discovery is the estimated body mass of the two individuals. The dinosaur Psittacosaurus lujiatunensis was about three times more massive than the mammal Repenomamus robustus. Despite the significant size difference, the fossil association is still within the 95% predictive range for a linear model of maximum prey body mass versus carnivore body mass. meat among terrestrial carnivores. This analysis indicates that the size difference between the two warriors is not an insurmountable obstacle for mammals, challenging the notion that predators typically target prey that are large in size. close to them.
Implications for understanding the Mesozoic ecosystem
Indeed, modern-day examples of small carnivorous mammals preying on much larger animals demonstrate the plausibility of such an encounter. For example, it is known that coyotes sometimes attack prey many times their size, such as elk and reindeer. This similarity suggests that the small mammal, Repenomamus robustus, may have had similar hunting abilities and could have been a formidable hunter even for relatively large dinosaurs.
The discovery of this ancient battle site not only provides insight into predator-prey interactions during the Mesozoic period, but also highlights the exceptional conservation potential of eroding sediments. due to catastrophic events such as volcanic debris flows. The Lujiatun member of the Yixian Formation, often referred to as the “Chinese Pompeii”, played an important role in revealing the diverse fauna of small-bodied dinosaurs and other creatures from this period. As research in the area continues, paleontologists anticipate further fossil discoveries that may shed more light on dinosaur-mammal interactions as well as the ecological dynamics of the dinosaurs. this ancient world.
Despite their smaller size, this mammal’s predation on dinosaurs challenges the common assumption that Mesozoic mammals were merely dependent on dinosaurs. larger than them. Fossils provide evidence that Mesozoic mammals were more than mere bystanders and could pose a real threat even to adult dinosaurs. Such insights into the dynamics of ancient ecosystems are invaluable for understanding the complex interactions between species and the factors that shape their evolutionary trajectories.
Jordan Mallon, paleontologist at the Canadian Museum of Nature in Ottawa and co-author of the study, said:
“Although the fossil beds in the Lujiatun area are highly productive, there are still many unanswered questions about this ancient ecosystem. There is a tendency that those fossil beds preserve only the small animals that existed at the time. Perhaps the larger dinosaurs were able to escape the volcanic landslide that the smaller animals fell victim to, so I would love to know more about the large animals that lived in that area, which requires asked to continue the study”.
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Source: pagasa.edu.vn