Although the gap in Hell Creek is particularly extreme, most communities with megateropods that the researchers study had no carnivores between 220 and 660 pounds. (For a modern comparison, it is as if the adult carnivores in the Kruger National Park in South Africa are all larger than a lion or smaller than a bat’s ear, they write.)
In the individual communities, the gaps in the carnivorous animals were more apparent than in the lack of megatopatrons, which supports the idea that the young megatopatrons fill them, Ms. Schroeder said. The gaps also did not apply to herbivores. This suggests that the inability of the young carnivores to hunt the same food as adults forced them to carve out their own niche, which had a strong impact on the ecosystem. (In contrast, a baby sauropod can feast on the lower branches of a tree while an adult eats the top.)
The new study ‘represents an enormous achievement in testing this concept’, said dr. Clauss said. Theoretically, he said, the same dynamics would have made it more difficult for dinosaurs to repopulate large niches after a mass extinction event: When the large dinosaurs died, the relative lack of small and medium-sized species meant that mammals were better able to was to take over.
Broad analyzes like these are a true ‘field transformation’ of paleontology, says Lawrence M. Witmer, a professor of anatomy and paleontology at the University of Ohio who was not involved in the study.
“The idea that young people were different kinds of predators than their monster parents was there,” said Dr. Witmer said. But although many paleontologists have focused on one species at a time to address this question, this new study connects rather “thousands of dots,” he said, to show how entire communities of dinosaurs evolved.
“It’s a big problem,” he said.
At the same time, the lack of juvenile dinosaur fossils makes it difficult to understand exactly the roles that young people played, said David Hone, a zoologist at Queen Mary University of London, who used similar methods to study the distribution of dinosaurs.
“Knowing that youths have filled a common niche space and can actually do something with the information is two different things,” he said.