If you’ve seen any of the Jurassic Park movies, you’d know that the most feared dinosaur among the other others is actually the carnivore, the T-Rex.
But were the T-Rexes really the most dangerous dinosaurs out there? The huge meat-eating dinosaurs such as Tyrannosaurus rex - sometimes topping 9 tons in weight as adults - ruled the Cretaceous Period landscape.
But even as juveniles, scientists said on Thursday, these fearsome species - together called megatheropods - dramatically reshaped the composition of dinosaur communities around the world, crowding out midsized carnivorous competitors.
Researchers examined dinosaur communities - the species of meat-eaters and plant-eaters inhabiting the same place at the same time - in 43 locations globally during the Jurassic and Cretaceous Periods, spanning the final 136 million years of the dinosaur age.
Carnivorous dinosaurs came from a group called theropods. The largest were the megatheropods, bipedal brutes with large skulls, strong jaws and menacing teeth.
Paleo-ecologists from The University of New Mexico and at the University of Nebraska-Lincoln have demonstrated that the offspring of enormous carnivorous dinosaurs, such as Tyrannosaurus rex may have fundamentally re-shaped their communities by out-competing smaller rival species.
The study, released this week in the journal Science, was the first to examine community-scale dinosaur diversity while treating juveniles as their own ecological entity.
“Dinosaur communities were like shopping malls on a Saturday afternoon — jam-packed with teenagers," explained Kat Schroeder, a graduate student in the UNM Department of Biology who led the study. “They made up a significant portion of the individuals in a species and would have had a very real impact on the resources available in communities."
Cretaceous dinosaur communities that included a megatheropod - defined as a predator weighing at least a ton - were also populated with small predators - under about 220 pounds (100 kg) - but typically lacked midsized meat-eaters between those two weight ranges.
This “gap" appears to have been caused by the presence of juvenile megatheropods that grew from babies the size of a small dog into teenage terrors before achieving adult dimensions.
These juveniles filled an ecological niche - using a unique set of physical attributes to target intermediate-sized prey - that otherwise might have been occupied by another species.
“Just like when parents drop their teens off at the mall to get them out of their hair, Mesozoic communities might have been separated by ages, with adult megatheropods hunting and consuming in their own way, while juveniles of the same species were doing something completely different," Kat Schroeder further told Reuters.
Because they were born from eggs, dinosaurs like T. rex necessarily were born small — about the size of a house cat. This meant as they grew to the size of a city bus, these “megatheropods," weighing between one and eight tons, would have changed their hunting patterns and prey items. It’s long been suspected by paleontologists that giant carnivorous dinosaurs would change behavior as they grew. But how that might have affected the world around them remained largely unknown.
Juveniles of North American Cretaceous megatheropods like Tyrannosaurus and Albertosaurus were relatively light and agile, Schroeder noted, making them well-suited to hunt different prey, compared with bigger and bulkier adults with bone-crushing jaws and proportionally shorter legs.
These dinosaurs lived to roughly age 40, with big growth spurts as teens.
Adding to their behaviour, a study in early January found from embryonic remains from the group of ferocious meat-eating dinosaurs that includes T. rex - fossilized jaw and claw bones that show these record-size babies looked a lot like adults and were “born ready” to hunt.
The jaw possesses distinctive tyrannosaur traits, including a deep groove inside and a prominent chin. It appeared that tyrannosaurs were “born ready to hunt, already possessing some of the key adaptations that gave tyrannosaurs their powerful bites. So it’s likely that they were capable of hunting fairly quickly after birth."