February 26, 2021 10:37:22 AM IS
A team of American scientists has shown that the offspring of huge carnivorous dinosaurs like Tyrannosaurus rex, which grew from the size of a house cat to huge monsters, reshaped their ecosystems and outpaced smaller rival species. Their study, published in the journal Science Thursday, helps answer a lingering mystery about the reign of the dinosaurs 150 million years ago: why were there so many more large species than small ones, which is the opposite of what we see in land animals today?
Dinosaurs weren’t particularly diverse: There are only 1,500 known species, compared to tens of thousands of modern species of mammals and birds.
“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 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 taking into account the limits of the fossil record, on I think that in the assembly, the dinosaurs are particularly diversified: they are not 1500 known specimens, against the tens of thousands of modern species of mammals and birds
Also, throughout the Mesozoic Era, 252 to 66 million years ago, there were relatively more species of large dinosaurs weighing 1,000 kilograms (one ton) compared to species that weighed less than 60 kilograms (130 pounds).
Some scientists have proposed the idea that since even the most gigantic dinosaurs start life as tiny newborns, they could use different resources as they age, taking up space in ecosystems where smaller species might otherwise thrive.
To test the theory, Schroeder and his colleagues analyzed data from fossil sites around the world, including more than 550 species of dinosaurs, and arranged dinosaurs according to whether they were herbivores or carnivores, along with their size.
They discovered a surprising gap in the presence of medium-sized carnivores in every community that had megaheropods or giant predators like the T-rex.
“There are very few carnivorous dinosaurs between 100 and 1,000 kilograms (200 pounds per ton) in communities that have megatheropods,” said Schroeder. “And the juveniles of these megaheropods fit perfectly in this space. “
Treat juveniles like a species
The conclusion was supported by how dinosaur diversity 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 larger ones.
This is because the Jurassic megatheropod adolescents looked more like adults and there was a greater variety of long-necked herbivorous sauropods (such as 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 certain ages by the number expected to survive each year, according to the fossil record.
This statistical method, which effectively treated the juveniles as their own species, perfectly eliminated the deficiencies observed in medium-sized carnivores.
In addition to helping to answer a long-standing question, the research shows the value of applying ecological considerations to dinosaurs, Schroeder said.
“I think we’re moving a little bit more toward understanding dinosaurs as animals rather than looking at dinosaurs as fresh rocks, that’s where paleontology began and has been for a long time,” she says.