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Teenage T rex and other carnivorous dinosaurs the size of lions or bears may have crowded out the smaller species, explaining why there are so few preserved in the fossil record, research suggests.
Although they ruled the earth for over 150 million years, dinosaurs were not particularly diverse, and the best-known species were giants weighing 1,000 kg or more – including massive carnivorous megatheropods such as Tyrannosaurus rex.
The smallest dinosaurs weighing less than 60 kg are particularly absent from the fossil record. This is very different from other vertebrate communities, which generally contain a broad spectrum of body sizes.
Now a study published in Science has provided an explanation: Megatheropods may have taken a ‘grow fast, die young’ approach that meant the Earth was filled with meat-eating teens occupying ecological niches that would otherwise have hosted smaller carnivores.
To test this theory, Katlin Schroeder of the University of New Mexico and her colleagues analyzed a dataset of dinosaur records representing 43 communities geographically located on seven continents, spanning 136 million years. This confirmed that communities containing megatheropods were largely devoid of medium-sized carnivores in the 100-1000 kg range, while those without megatheropods contained these species.
Using existing information on the growth rates of these dinosaurs and the age at which they died, they also calculated that the juveniles must represent a substantial proportion of the total megatheropod population – enough to have beaten adults of similar size. of different species.
“Not only were there a lot more juveniles than adults, but they would have been right in that mass range that we lack in other species,” said Schroeder. These young megatheropods may have occupied a different ecological niche than adults – just as Komodo dragons do today, with their young hatched from eggs, scurrying into trees and eating insects and lizards, until they get too big and then fall to the ground start hunting bigger creatures, from rodents to water buffaloes.
“One thing that stands out about megatheropods is that as they got older they changed a lot,” said Schroeder. “An adult Tyrannosaurus rex was this huge, sturdy, bone-cracking animal, but as juveniles they were quite light, with floating legs, and did not have deep, heavy skulls. They may have been the same genetic species, but their appearance and function were entirely different.
Steve Brusatte, professor of paleontology and evolution at the University of Edinburgh, said: “This study puts numbers on something we have long suspected but haven’t really proven: that the largest carnivorous dinosaurs occupied different niches in the food chain as they moved from miniature hatchlings to adults.” bigger than the buses.
“This seems to be a constant trend among dinosaurs, especially in Cretaceous communities, towards the end of their reign. There were few species of moderate adult-sized meat-eating dinosaurs, and this is because juveniles, teens, and sub-adults of large bruised dinosaurs controlled these niches. It is an ecological structure that is very different from what we are used to with mammals today.
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