'Tiny' new T-Rex ancestor unearthed in China
A relatively tiny new ancestor of the Tyrannosaurus rex has been
unearthed in China, researchers said Thursday.
The three-meter-long (10-foot-long) dinosaur dubbed the Raptorex only
weighed about 60 kilograms (150 pounds) and was nearly 100 times smaller
than the king of the dinosaurs.
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, said lead author Paul Sereno, a paleontologist with the
University of Chicago.
A model of the Tyrannosauru rex |
"It was jaws on legs," Sereno said.
This unexpected new link in the evolution of the mighty predator
which once dominated the northern half of the globe has provided
researchers with an entirely 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.
"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."
The Raptorex fossil shows that the skinny arms evolved not in order
to help the growing tyrannosauruses offset a heavier overall bodyweight,
but instead as a tradeoff for agility and speed. The powerful muscles of
the back legs would have helped the T. Rex chase down its prey while the
smaller front legs allowed it to remain upright and attack with its
deadly jaws. The Raptorex fossil - which was estimated to be a juvenile
of five to six years old when it died - is about 125 million years old.
The tyrannosaurus genus did not reach its full size until about 85
million years ago and was wiped out about 65 million years ago in the
great extinction which ended the Cretaceous Period.
"What that means is that for most of their evolutionary history,
about 80 percent of the time that they were on earth, tyrannosauruses
were small animals that lived in the shadow of other types of very large
dinosaur predators," Brusatte said in a conference call with reporters.
It's likely that T. Rex was able to grow to its colossal size because
other competing predators became extinct, Sereno said.
"We cannot say that this incredibly successful, scalable blueprint
for a predator was responsible for their total domination... because we
never saw them cohabiting in environments with these other, earlier
types of predators," he said.
But once tyrannosauruses were able to expand in body size, "there was
no turning back until the asteroid hit because they really had it down
pat."
The incredibly well-preserved and nearly complete fossil was almost
lost to science after it was unearthed illegally and spirited out of
China for sale on the private market.
An American eye surgeon and dinosaur enthusiast purchased the
still-embedded fossil and recognized its potential value to science.
Henry Kriegstein contacted Sereno, who agreed to analyze the fossil so
long as Kriegstein was willing to return it to China once the work is
complete. "We rapidly achieved that agreement and Raptorex sees the
light of day," Sereno said. AFP |