Ltheir study, published Thursday in the prestigious journal Science, helps answer a lingering mystery about the 150 million years or so that dinosaurs ruled: why were there so many more species large in size than small, when the reverse is true in animals terrestrial today?
“The dinosaur communities were like shopping malls on Saturday afternoons, filled with teenagers,” says Kat Schroeder, a researcher at the University of New Mexico, who led the study. These “adolescents” represented “a significant portion of individuals of a species and apparently had a real impact on the resources available in their communities,” she explained.
Even with a limited number of fossils, experts believe that globally, dinosaurs were not very diverse: there are only around 1,500 known species, compared to tens of thousands of species of mammals and birds today. hui. And over the entire Mesozoic era, between 252 and 66 million years ago, there were relatively more species of large dinosaurs weighing a ton, compared to those weighing less than 60 kg.
According to some scientists, knowing that even the largest dinosaurs start their life with a very small size since they are in eggs before birth, it could be that they occupy the resources of smaller species, in ecosystems where they would normally have been queens.
To test this theory, Kat Schroeder and her colleagues looked at fossil data from around the world, from 550 different species, and organized dinosaurs by size and whether they were herbivores or carnivores.
They discovered a striking hole for medium-sized carnivorous dinosaurs in any community where mega-theropods were found, or giant predators like Tyrannosaurus rex.
“Very few carnivorous dinosaurs between 100 and 1,000 kilograms exist in communities with mega-theropods,” explains Kat Schroeder. And young mega-theropods fill exactly that space. ” This conclusion is supported by how the diversity of dinosaurs has evolved over time. The Jurassic era (between 200 and 145 million years ago), had smaller holes in this category, when the Cretaceous era (between 145 and 65 million years ago), had very large holes. .
This is because the adolescent mega-theropods of the Jurassic era looked more like adults, and there was a greater variety of herbivores for them to hunt. “The Cretaceous, on the other hand, is totally dominated by Tyranosaurs and abelisaurs, which evolve a lot when they grow up”, detailed the researcher.
“I think we are slowly starting to understand dinosaurs as animals, and no longer to look at them as cool objects, which is where paleontology left, and where it has been for a long time,” s’ she is delighted with AFP.