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A team of American scientists has demonstrated that the offspring of huge carnivorous dinosaurs like Tyrannosaurus rex, which grew from the size of domestic cats to towering monsters, reshaped their ecosystems ahead of smaller rival species.
Their study, published in the journal Science Thursday, helps answer a lingering mystery about the 150 million year old rule of dinosaurs: why were there many more large species than small, which is the opposite of what we see in land animals today ‘hui?
“The dinosaur communities were like shopping malls on a Saturday afternoon, packed with teenagers,” said Kat Schroeder, a University of New Mexico graduate student 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 on the whole, dinosaurs were not particularly diverse: there are only 1,500 known species, compared with tens of thousands of modern species of mammals and mammals. birds.
Additionally, throughout the Mesozoic Era, 252-66 million years ago, there were relatively many more species of large bodily dinosaurs weighing 1000 kilograms (one ton) compared to species weighing less than 60 kilograms. (130 pounds).
Some scientists have put forward the idea that since even the most gigantic dinosaurs start their lives as tiny newborn babies, they might use different resources as they grow older – occupying space in ecosystems where smaller species might otherwise thrive.
To test the theory, Schroeder and his colleagues looked at data from fossil sites around the world, including more than 550 species of dinosaurs, and organized the dinosaurs according to whether they were herbivores or carnivores, along with their sizes.
They discovered a striking gap in the presence of medium-sized carnivores in every community that had megatheropods, or giant predators like the T. rex.
“Very few carnivorous dinosaurs between 100 and 1,000 kilograms (200 pounds per ton) exist in communities that have megatheropods,” Schroeder said.
“And the juveniles of these megateropods fit perfectly into this space.
Treat juveniles as a species
The conclusion was supported by how the diversity of dinosaurs has evolved over time. Jurassic communities (200 to 145 million years ago) had smaller gaps and Cretaceous communities (145 to 65 million years ago) had large ones.
This is because the adolescents of Jurassic megateropods looked more like adults and there was a greater variety of long-necked herbivorous sauropods (like the brachiosaurus) for them.
“The Cretaceous, on the other hand, is completely dominated by tyrannosaurs and abelisaurs, which change a lot as they grow,” said Schroeder.
To mathematically test their theory, the team multiplied the mass of juvenile megatheropods at given ages by the number that was expected to survive each year, based on the fossil record.
This statistical method, which effectively treated juveniles as their own species, completely eliminated the shortcomings observed in medium-sized carnivores.
In addition to helping solve a long-standing question, research shows the value of applying ecological considerations to dinosaurs, Schroeder said.
“I think we are moving a bit more towards understanding dinosaurs as animals rather than looking at dinosaurs as just fresh rocks, that’s where paleontology started and has been for a long time,” he said. she declared.
© Agence France-Presse
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