A dinosaur with a large skull but short arms – that sounds like T. rex. But he wasn’t the only primeval giant with extremely short forelimbs: a team of paleontologists made an “exciting find” with the bones of a previously unknown predatory dinosaur in Patagonia.
In Patagonia, paleontologists have unearthed the bones of a predatory dinosaur that, with its large skull and short arms, is reminiscent of the famous T. rex. Despite the external similarity, the two dinosaurs are not related to each other, the researchers report in the journal Current Biology. Meraxes gigas, as the new carnivore is called, and T. rex evolved their disproportionately short arms independently. What they use them for is still unclear.
During the excavations in the so-called “Huincul Formation” in what is now northern Patagonia, the researchers found skull fragments, shoulder, pelvic and foot bones, a connected series of caudal vertebrae as well as ulna, tibia and calf bones. According to the researchers, the remains form the most complete fossil of a Carcharodontosauridae representative that has ever been found in the southern hemisphere.
Carcharodontosauridae denote a kinship of large theropods that lived in the Cretaceous period and included giant predatory dinosaurs. Meraxes gigas was just such a gigantic predator: The discovered specimen, around 45 years old, was eleven meters long and weighed more than four tons when it was alive, the researchers report. Its skull, which is about 1.27 meters long, was decorated with crests, furrows, bumps and squirrels.
“These traits appeared late in development, when the animals became adults,” explains lead author Juan Canale of the Ernesto Bachmann Paleontological Museum in Neuquén, Argentina, in a statement. Presumably, they served to attract potential mates: “Sexual selection is one powerful evolutionary force. But since we can’t directly observe their behavior, it’s impossible to be sure.”
The researchers are certain, however, that Meraxes gigas did not get its noticeably short arms from Tyrannosaurus Rex or vice versa: On the one hand, M. gigas died out almost 20 million years before T. rex emerged. On the other hand, the two species are very far apart in the evolutionary tree. “There is no direct relationship between the two,” Canale clarifies.
However, if such short arms developed independently in different theropod species, one must assume that the shortened limbs had a specific function – and they did not simply shrink because they were useless to the dinosaurs. In addition, the skeleton showed large muscle attachments and fully developed pectoral girdles. “So the arm had strong muscles,” concludes project leader Canale. However, this muscle power was probably not used for hunting, because “actions associated with catching prey were most likely performed with the head,” argues the paleontologist.
Canale speculates, “They may have used the arms for reproduction, such as holding the female during mating.” It is also conceivable that the limbs were helpful in order to get up again after a fall.
For Juan Canale, the discovery of the well-preserved fossil represents “probably the most exciting point” in his career – however, fantasy friends in particular should be happy about the choice of name for the new species of dinosaur: As the study authors write, Meraxes is after a dragon from the epic “A Song of Ice and Fire” by the American writer George R.R. Martin, which was filmed with the series “Game of Thrones”.
