The most famous of all dinosaurs, Tyrannosaurus rex, managed to be fearsome enough to star posthumously in a Hollywood blockbuster despite its comically short arms. Some other, lesser-known dinosaurs also combined a large head with short forelimbs, and a study published today (July 7) in Current Biology identifies yet another, which lived 20 million years before T. rex and belonged to an entirely different group—suggesting there was likely an evolutionary advantage to the combo.
“For a long time, we thought it was mostly tyrannosaurs that did the big head, long legs, small arms thing,” James Napoli at the American Museum of Natural History in New York, who wasn’t involved in the research, tells New Scientist. The study reveals that Meraxes gigas, which belongs to a group called carcharodontosaurs, also sported those physical characteristics.
The results are based on fossils, including M. gigas’s skull and limbs, that the study authors unearthed in Argentina in 2012. They estimate that M. gigas, named after a dragon from Game of Thrones, was 11 meters long and weighed around 4 metric tons. It lived during the Late Cretaceous epoch, around 95 million years ago.
While the ancestors of M. gigas had longer arms, study coauthor Juan Canale of the Ernesto Bachmann Paleontological Museum in Argentina tells CNN that they likely shrank as the animals developed larger, more powerful heads, with which they could have grabbed prey directly, leaving their arms unnecessary for hunting. Although short, M. gigas’s arms were strong, indicating they retained some other function, according to the study. “I’m inclined to think that they were used in other kinds of activities, like holding the female during mating or help in raising the body from a prone position,” Canale tells Reuters.
Smithsonian reports that the M. gigas fossils are also shedding light on the anatomy of other species of carcharodontosaurs, which are largely known from fossil remains much less complete than those of M. gigas.
“Every new, weird, unexpected dinosaur is really important in reminding us just how much is left to be discovered,” Napoli tells New Scientist.