The Tyrannosaurus rex was a killing machine. This terrible predator reached four meters in height, exceeded twelve in length and the largest specimens weighed eight tons. His bite, delivered with a force of 35,400 newtons, was the most powerful of any land animal ever. However, beasts were not born made. When hatched from the egg, the tiny tyrannosaurs were about the size of a house cat. This meant that as they grew to the size of a city bus, they had to change their prey and hunting patterns. These behavioral changes, a new study published in the journal “Science” concludes, greatly affected the world that gnawed on them. So much so that they even swept away other smaller rival species that competed for food in the same ecosystem.

“Dinosaur communities were like shopping malls on a Saturday afternoon, full of teenagers,” jokes Kat Schroeder, a paleoecologist at the University of New Mexico (USA) and head of the study. “They were an important part of the individuals of a species and would have had a very real impact on the resources available in the communities,” he adds. In his view, these juvenile tyrannosaurs could be assuming the role of multiple species as they grew, limiting the number of actual species that could coexist in a community. The truth is that the number of different types of dinosaurs known around the world is low, particularly among small species. To address this low diversity, the team collected data from known fossil sites around the world, including more than 550 species of dinosaurs. Organizing the dinosaurs by mass and diet, they examined the number of small, medium, and large species in each community.

They found a surprisingly clear pattern. in communities, with megaterropods (any theropod dinosaur that exceeds four tons and ten meters in length, such as the tyrannosaurus) there were very few carnivorous dinosaurs between 100 and 1000 kilos, a space in which the juveniles fit perfectly. of the megateropodos. Diversity over time Observing the diversity of dinosaurs overtime was key to the study. Jurassic communities (200-145 million years ago) had smaller gaps while those of the Cretaceous (145-65 million years ago) were larger. For Schroeder, the reason is that the large Jurassic theropods did not change as much as they grew: adolescents looked more like adults, which made room for other smaller carnivores. However, the Cretaceous was dominated by tyrannosaurs and abelisaurs, which change a lot as they grow older. Schroeder thinks this research is important because it clarifies (at least partially) why dinosaur diversity was lower than expected based on other fossil groups. It also explains why there are many more very large dinosaur species than small ones, which is the opposite of what you might expect. But the most relevant thing, he adds, is that it shows the results of the growth of dinosaurs from very small hatchlings to gigantic adults in an ecosystem.