A team of US scientists has shown that the descendants of giant carnivorous dinosaurs like them Tyrannosaurus rex, which have grown from the size of domestic cats to towering monsters, have reshaped their ecosystems by surpassing smaller rival species.
Their study, published in the journal Science on Thursday, it helps answer a long-standing mystery about the 150 million-year-old dinosaur rule: why were there 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 teenagers,” said Kat Schroeder, a graduate student at the University of New Mexico who led the research.
“They were a significant 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 fossil records, 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.
Moreover, throughout the Mesozoic era, 252 to 66 million years ago, there were relatively many species of large-bodied dinosaurs weighing 1,000 kilograms (one tonne) compared to species weighing less. of 60 kilograms (130 kilograms).
Some scientists have proposed the idea that since even the most giant dinosaurs start life as small seedlings, they could use different resources as they grew – taking up space in ecosystems where smaller species could otherwise 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 herbivores or carnivores, as well as their size.
They found a striking gap in the presence of medium-sized carnivores in each community that had megateropods or huge predators such as T. rex.
“Very few carnivorous dinosaurs between 100 and 1,000 kilograms (200 pounds to a ton) exist in communities that have megateropods,” Schroeder said.
“And the minors of those megateropods fall right into that space.”
Treating young people as a species
The conclusion was supported by the way in which the diversity of dinosaurs changed over time. Jurassic communities (200-145 million years ago) had smaller gaps, and Cretaceous communities (145-65 million years ago) had large communities.
This is because Jurassic megateropod adolescents were more like adults and there was a wider variety of long-necked herbivorous sauropods (such as brachiosaurus) to prey on.
“The Cretaceous, on the other hand, is completely dominated by tyrannosaurs and abelisaurs, which change a lot as they grow,” Schroeder said.
To test their theory mathematically, the team multiplied the juvenile mass of megateropods at given ages by what they expected to survive each year, based on fossil records.
This statistical method, which effectively treated the young as its own species, carefully eliminated the observed gaps of medium-sized carnivores.
Beyond helping solve a long-term question, the research shows the value of applying ecological considerations to dinosaurs, Schroeder said.
“I think we’re moving a little bit closer to understanding dinosaurs as animals, as opposed to looking at dinosaurs as cold rocks, where paleontology started and has been for a long time,” she said.
© Agence France-Presse