The fossils of a new kind of dinosaur reminiscent of a Tyrannosaurus rex for its large head, sharp teeth, and puny arms were discovered in Argentina and designated a new species named Meraxes gigas. The Meraxes, or M. gigas for short, was unearthed in northern Patagonia in 2012, and over a decade-long period researchers studied and compared the bones to make sure they identified a new dinosaur, announcing the discovery in Current Biology on July 7.
The generic name was derived from “Meraxes”, a dragon from George R. R. Martin’s fantasy novel series A Song of Ice and Fire. The specific name, “gigas”, comes from a Greek word meaning "giant.” The dinosaur is estimated to have been 11 meters long and weighed roughly 4 tons, its skull covered with crests, bumps, and small horns. Meraxes also is believed to have lived much longer than a T. rex. The dinosaur discovered in Argentina is believed to have been about 45 years old—more than 20 years older than the normal lifespan of a T. rex.
The Meraxes provides new insight into the evolution of predatory dinosaurs.
Although Meraxes looks similar to a T. rex, the researchers contend that it comes from a different group of dinosaurs called the Carcharodontosauridae which lived around 20 million years before, during the Early Cretaceous period. Previously, predators of that size with large heads, long legs, and small arms had mostly been attributed to the same group as the Tyrannosaurus. But the discovery of the similar characteristics in an unrelated species millions of years apart shows that both creatures evolved independently to embody the same physical trait. Scientists have various ideas as to why this happened.
Juan Ignacio Canale, one of the Argentine researchers who found the fossils, told New Scientist that “those proportionally tiny arms had some sort of function.” Canale said that researchers found that Meraxes’ arm muscles were well developed, suggesting they were used. Canale believed that Meraxes might have used their arms to set themselves straight after falling down or to hold a partner during mating.
The researchers also argued that the small size of the arms could be directly related to their massive skulls, as the evolutionary process counterbalances one with the other. The characteristics developing independently in unrelated groups of dinosaurs provides support for that hypothesis, the scientists wrote.
The Meraxes discovered in Argentina is believed to have died in a muddy area near a river. At some point, the river changed and brought sand that covered the mud and deposited a thick layer above the bones that turned into a few feet of sandstone. That was one of the reasons the bones went undiscovered for so long.
The fossils of Meraxes are being displayed in the Ernesto Bachmann museum in Villa El Chocon, Argentina. It's only a matter of time before the newly discovered giant predator makes an appearance as the latest antagonist in an upcoming incarnation of the Jurassic Park franchise.