A team of American scientists has shown that the offspring of huge carnivorous dinosaurs such as Tyrannosaurus RexGrowing from the size of house cats to towering monsters, they reshaped their ecosystems by defeating smaller rival species.
Their study, published in the journal Sciences Thursday, it helps answer an enduring mystery about the 150-million-year-old dinosaur rule: why were there so many more large species compared to small ones, which is the opposite of what we see in land animals today?
“Dinosaur communities were like shopping malls on a Saturday afternoon, packed with teenagers,” said Kat Schroeder, a graduate student at the University of New Mexico who led the research.
“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.”
Even given the limitations of the fossil record, it is believed that overall, dinosaurs were not particularly diverse – there are only about 1,500 known species, compared to tens of thousands of modern species of mammals and birds.
What’s more, throughout the Mesozoic era, from 252 to 66 million years ago, there were relatively many more species of large-bodied dinosaurs that weighed 1,000 kilograms (one ton) compared to species that weighed less than 60 kilograms (130 pounds). .
Some scientists put forward the idea that since even the most gigantic dinosaurs begin life as tiny hatchlings, they could be using different resources as they grew, occupying space in ecosystems where smaller species could otherwise flourish.
To test the theory, Schroeder and his colleagues examined data from fossil sites around the world, including more than 550 species of dinosaurs, and organized the dinosaurs by whether they were herbivores or carnivores, as well as their size.
They discovered a striking gap in the presence of medium-sized carnivores in each community that had megatheropods, or giant predators like the Tyrant Saurus Rex.
“There are very few carnivorous dinosaurs between 100 and 1000 kilograms (200 pounds to one ton) in communities that have megaheropods,” said Schroeder.
“And the juveniles of these megaheropods fit perfectly in that space.”
Treat juveniles as a species
The conclusion was supported by the way that dinosaur diversity changed over time. Jurassic communities (200-145 million years ago) had smaller gaps and Cretaceous communities (145-65 million years ago) had larger ones.
That’s because the teenagers of the Jurassic megaheropods were more like adults, and there was a wider variety of long-necked herbivorous sauropods (like the brachiosaurus) for them to feed on.
“The Cretaceous, on the other hand, is completely dominated by tyrannosaurs and abelisaurs, which change a lot as they grow,” Schroeder said.
To mathematically test their theory, the team multiplied the mass of juvenile megatheropods at ages determined by the number expected to survive each year, based on fossil records.
This statistical method, which effectively treated juveniles as their own species, perfectly squared the gaps observed in medium-sized carnivores.
Beyond helping to answer a long-standing question, the research shows the value of applying ecological considerations to dinosaurs, Schroeder said.
“I think we’re shifting a little bit more toward understanding dinosaurs as animals rather than looking at dinosaurs as cold rocks, which is where paleontology began and has been for a long time,” he said.
© Agence France-Presse