Tiny arms might be useful for T-Rex sex

There’s a new dino on the block. Meet Meraxes gigas.

The discovery of this individual (or what remains of it) has been announced by a research team working in Argentina’s Patagonia region.

Named after a dragon from the popular A Song of Ice and Fire/Game of Thrones book and TV series, Meraxes and its 11-metre-long kin roamed the region during the Late Cretaceous period – about 95 million years ago.

And while the illustrated imaginings of this four-tonne carnivore bear a striking resemblance to Tyrannosaurus rex, the two never shared the stage. Meraxes lived about 20 million years before T-Rex came onto the scene, but it’s the fact that both share tiny arms that has researchers fascinated.

While predation was a duty likely performed by the head (picture T-Rex chomping on a raptor in Jurassic Park), short arms may have evolved separately in both species to perform other roles.

Usefulness in dino sex is one possibility.

“There is no direct relationship between both [T-Rex and Meraxes],” explains the project’s lead, Juan Canale from the Ernesto Bachmann Paleontological Museum in Neuquénm, Argentina. “I’m convinced that those proportionally tiny arms had some sort of function. The skeleton shows large muscle insertions and fully developed pectoral girdles, so the arm had strong muscles.

“They may have used the arms for reproductive behaviour such as holding the female during mating or [to] support themselves to stand back up after a break or a fall.”

Meraxes belonged to a family of dinos known as the Carcharodontosaurids, a group that includes other heavyweights like the 15-metre long Carcharodontosaurus, and the eight-tonne Gigantosaurus.

The discovery published in Current Biology show complete regions of Meraxes’s skeleton, including the arms, legs, pelvis and part of the ‘tail’ vertebrae.

The remains notably show ‘ornamented’ dermal bones and the skull consists of furrows, bumps and ridges. The researchers believe these may have been useful in mate attraction.

“That helped us to understand some evolutionary trends and the anatomy of Carcharodontosaurids,” says Canale. “The fossil has a lot of novel information, and it is in superb shape.

“Ornamentations appear late in the development when the individuals became adults. Sexual selection is a powerful evolutionary force, but given that we cannot directly observe their behaviour, it is impossible to be certain about this.”