CHICAGO: At just 1% of the size of its later relative, a tiny new ancestor of Tyrannosaurus rex has been unearthed in China.
The three-metre-long dinosaur dubbed Raptorex only weighed an estimated 60 kg, but it was nearly identical in structure - even down to the scrawny arms - and had all of the traits which made T.rex such a successful predator.
"It was jaws on legs," said lead author Paul Sereno, lead author a study which details the find and a palaeontologist with the University of Chicago in Illinois, USA. New picture of evolution
This unexpected new link in the evolution of the mighty predator which once dominated the northern half of the globe is offering a completely new picture of how T.rex evolved. "Raptorex, the new species, really throws a wrench into the observed pattern," said co-author Stephen Brusatte of the American Museum of Natural History in New York City.
"Here we have an animal that's 1/100th of the size of T.rex, about my size, but with all of the signature features - big head, strong muscles, tiny little arms - that were thought to be necessary adaptations for a large-body predator," he said. Raptorex shows that the skinny arms evolved not in order to help it offset a heavier overall bodyweight, but instead as a trade-off for agility and speed. The powerful muscles of the back legs would have helped the species to chase down its prey while the smaller front legs allowed it to remain upright and attack with its deadly jaws.
The fossil - which was estimated to be a juvenile of five to six years old when it died - is about 125 million years old.
The three-metre-long dinosaur dubbed Raptorex only weighed an estimated 60 kg, but it was nearly identical in structure - even down to the scrawny arms - and had all of the traits which made T.rex such a successful predator.
"It was jaws on legs," said lead author Paul Sereno, lead author a study which details the find and a palaeontologist with the University of Chicago in Illinois, USA.
New picture of evolution
This unexpected new link in the evolution of the mighty predator which once dominated the northern half of the globe is offering a completely new picture of how T.rex evolved. "Raptorex, the new species, really throws a wrench into the observed pattern," said co-author Stephen Brusatte of the American Museum of Natural History in New York City.
"Here we have an animal that's 1/100th of the size of T.rex, about my size, but with all of the signature features - big head, strong muscles, tiny little arms - that were thought to be necessary adaptations for a large-body predator," he said.
Raptorex shows that the skinny arms evolved not in order to help it offset a heavier overall bodyweight, but instead as a trade-off for agility and speed. The powerful muscles of the back legs would have helped the species to chase down its prey while the smaller front legs allowed it to remain upright and attack with its deadly jaws.
The fossil - which was estimated to be a juvenile of five to six years old when it died - is about 125 million years old.