A team of American scientists has shown that the descendants of huge carnivorous dinosaurs like Tyrannosaurus Rex, which went from the size of house cats to imposing monsters, reshaped their ecosystems by surpassing smaller rival species.
His study, published in the journal Science Thursday, helps answer a enduring mystery about the 150 million-year-old rule of dinosaurs: why were there so many more large species compared to small ones, which is the opposite of what we see in terrestrial animals today?
“Dinosaur communities were like shopping malls on a Saturday afternoon, full of young people,” said Kat Schroeder, a graduate student at the University of New Mexico who led the research.
“They formed an important part of the individuals of a species and would have had a very real impact on the resources available to communities.”
Even considering the limitations of the fossil record, it is believed that, in general, 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.
In addition, throughout the Mesozoic era, from 252 to 66 million years ago, there were relatively many more heavy-weight dinosaur species weighing 1,000 kilograms (one ton) compared to species weighing less than 60 kilograms. kilograms (130 pounds).
Some scientists raised the idea that since even the most giant dinosaurs begin life as small cubs, they could use different resources as they grew, occupying the space of ecosystems where otherwise smaller species could flourish. .
To test the theory, Schroeder and colleagues examined data from fossil sites around the world, including more than 550 species of dinosaurs, and organized dinosaurs according to whether they were herbivores or carnivores, as well as by their sizes.
They discovered a striking gap in the presence of medium-sized carnivores in all communities that had megateropods or giant predators such as the T. rex.
“There are very few carnivorous dinosaurs weighing between 100 and 1,000 kilograms (200 pounds a ton) in communities that have megateropods,” Schroeder said.
“And the minors of these megateropods fit directly into that space.”
Treatment of young people as a species
The conclusion was endorsed in the way the diversity of dinosaurs changed over time. Jurassic communities (200-145 million years ago) had smaller lagoons and Cretaceous communities (145-65 million years ago) had larger ones.
This is because adolescents in Jurassic megateropods looked more like adults and there was a wider variety of long-necked herbivorous sauropods (such as the brachiosaurus) that could take advantage.
“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 megateropods at certain ages by how many were expected to survive each year, according to fossil records.
This statistical method, which effectively treated minors as its own species, perfectly reduced the observed gaps in medium-sized carnivores.
Beyond helping solve 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 towards understanding dinosaurs as animals instead of considering them as fresh rocks, which is where paleontology started for a long time,” he said.
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