Paleontologists said Thursday they’d discovered a new giant carnivorous dinosaur species that had a massive head and tiny arms, just like Tyrannosaurus rex.
The researchers’ findings, published in the journal Current Biology, suggest that small forelimbs were not an evolutionary coincidence, but conferred certain survival advantages on top predators of the time.
Meraxes gigas – named after a fictional dragon in the Game of Thrones book series – was unearthed in field expeditions in Argentina’s northern Patagonia region over the course of four years, starting with the skull found in 2012.
“We won the lottery and literally found it on the first morning,” lead author Peter Makovicky of the University of Minnesota told AFP.
The fossilized remains were remarkably well preserved. The skull is just over four feet long (127 centimeters), while the entire animal would have been about 36 feet long and weighed four tons.
Its arms were two feet long, “so it’s literally half the length of the skull and the animal couldn’t have reached its mouth,” Makovicky said.
T. rex didn’t get its tiny arms from M. gigas. The latter died out 20 million years before the former emerged, and the two species were widely separated on the evolutionary tree.
Instead, the authors believe that the fact that tyrannosaurids, carcharodontosaurids — belonging to the group of meraxes — and a third giant predatory species called abelisaurs all evolved tiny arms suggests certain benefits.
Makovicky believes that as their heads grew larger, it became the dominant tool in their predatory arsenal, taking on the function that front legs would have served in smaller species.
His co-author Juan Canale, project leader at the Ernesto Bachmann Paleontological Museum in Neuquen, Argentina, went further and suggested other benefits.
– Mating and movement support –
“I am convinced that these proportionally tiny arms had some function. The skeleton shows large muscle attachments and fully developed pectoral girdles, so the arm had strong muscles,” he said in a statement.
“They may have used the arms for reproductive behaviors, such as holding the female during mating or bracing themselves to get back up after a pause or a fall.”
Meraxes roamed the Earth 90 to 100 million years ago during the Cretaceous Period, at a time when the region was wetter, more forested, and much closer to the sea, Makovicky said.
They would have hunted down a menagerie of contemporary sauropods – some of which have been spotted in the same location.
The individual lived to be around 40 years old — a ripe old age for dinosaurs — and its skull was covered with crests, grooves, bumps, and small hornets.
“It would certainly have looked very imposing and gargoyle-like,” Makovicky said.
“These are the types of traits that are often sexually selected in living animals,” speculated the species, which used its massive skulls as “billboards” to advertise potential mates.
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