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While the gap at Hell Creek is particularly extreme, most of the communities with megatheropods the researchers studied did not have carnivores between 220 and 660 pounds. (For a modern comparison, it’s as if the adult carnivores in South Africa’s Kruger National Park are all either bigger than a lion or smaller than a bat-eared fox, they write. )

The carnivore deficiencies were more pronounced in these individual communities than in those lacking megatheropods, supporting the idea that young megatheropods were filling them, Ms. Schroeder said. The gaps did not apply to herbivores either. This suggests that the inability of juvenile carnivores to hunt for the same food as adults has forced them to carve out their own niches, which has had a strong influence on the ecosystem, she said. (A baby sauropod, on the other hand, might munch on the lower branches of a tree while an adult ate the top.)

The new study “represents a huge feat to test this concept,” said Dr Clauss. Theoretically, he said, this same dynamic could have made it more difficult for dinosaurs to repopulate large niches after a mass extinction event: when large dinosaurs died, the relative lack of small and medium species. meant mammals were better placed to take over. .

Large analyzes like this “are really transforming the field” of paleontology, said Lawrence M. Witmer, a professor of anatomy and paleontology at Ohio University who was not involved in the study.

“The idea that the young were different types of predators than their monster parents was out there,” Dr Witmer said. But while many paleontologists have focused on one species at a time to answer this question, this new study instead connects “thousands of dots,” he said, to show “how entire communities of dinosaurs came to be. evolved”.

“It’s a big deal,” he said.

At the same time, the scarcity of juvenile dinosaur fossils makes it difficult to accurately understand the roles played by these young people, said David Hone, a zoologist at Queen Mary University in London who used similar methods to study the distribution of the size of dinosaurs.

“Knowing that young people were in a general niche and being able to do anything with that information are two different things,” he said.

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