A new species of dinosaur has been discovered in Argentina. Meraxes gigas existed 20 million years before T. rex and had a similar large body, sharp teeth, and proportionately small arms.

An artist's rendering of the recently discovered Meraxes gigas dinosaur.  Papolio, Carlos
An artist’s rendering of the recently discovered Meraxes Gigas dinosaur.  Papolio, Carlos

Meraxes Gigas, a recently discovered dinosaur species, had a massive body and small forelimbs like Tyrannosaurus rex. Both species’ proportionately tiny arms appear to have evolved independently.

The dinosaur was discovered in northern Patagonia, Argentina, in 2012, and paleontologists have been meticulously preparing and examining the skeleton ever since. Fortunately, the fossil was “very complete and exquisitely preserved,” according to Juan Ignacio Canale, a researcher at the Ernesto Bachmann Paleontological Museum in Villa El Chocón, Argentina. He explains that they compared the bones to those of other known species before concluding that it clearly represented a new species.

M. gigas, like T. rex, had sharp teeth, a large head and tail, and walked on two powerful legs. “For a long time, we thought it was mostly tyrannosaurs,” says James Napoli of the American Museum of Natural History in New York, who was not involved in the research. According to him, this fossil reveals that another group of dinosaurs known as carcharodontosaurs, which included M. gigas, was also following the same evolutionary pattern.

M. gigas was 11 metres long and weighed around 4 tonnes, according to the researchers. The species’ skull was adorned with crests, bumps, and small horns, and the individual recovered appears to have died at around 45 years of age, roughly twice the typical T. rex lifespan.

M. gigas roamed the planet around 95 million years ago, roughly 20 million years before T. rex, and the dinosaurs are very distantly related on the evolutionary tree. This suggests that small forelimbs on rather large dinosaurs evolved at least twice independently.

“Those proportionally tiny arms served a purpose,” Canale explains. The researchers could tell from the fossil that M. gigas’ arm muscles were well developed, implying that they were used. Canale believes they used their arms to hold a partner during mating or to help themselves right after a fall.

According to Napoli, the discovery of M. gigas serves as a reminder of how limited our understanding of dinosaurs is. “Every new, strange, unexpected dinosaur serves an important reminder of how much remains to be discovered.”

Reference: Current Biology, DOI: http://dx.doi.org/10.1016/j.cub.2022.05.057

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