Before T. rex made them fashionable, a newly discovered dinosaur had small arms.

The small, thick forelimbs of Meraxes gigas may have aided in mating.

A thousand scathing memes have been inspired by Tyrannosaurus rex's tiny arms: Can you pass the salt? Row, row, row your boat; I love you so much.

But hold back, snide jokers. These arms weren't simply an evolutionary joke, according to a newly discovered species of large-headed carnivorous dinosaur with short forelimbs. According to study published on July 7 in Current Biology, arm reduction and enormous heads both independently evolved in different dinosaur lineages.

Meraxes gigas, named for a dragon in George R. R. Martin’s “A Song of Ice and Fire” book series, lived between 100 million and 90 million years ago in what’s now Argentina, says Juan Canale, a paleontologist with the country’s CONICET research network who is based in Buenos Aires. Despite the resemblance to T. rex, M. gigas wasn’t a tyrannosaur; it was a carcharodontosaur — a member of a distantly related, lesser-known group of predatory theropod dinosaurs. M. gigas went extinct nearly 20 million years before T. rex walked on Earth.

According to Canale and colleagues, the M. gigas specimen they described was roughly 45 years old and over four tonnes in weight when it passed away. The 11-meter-long fossilised specimen had a richly decorated cranium with crests, bumps, and small hornlets, which likely served to attract mates.

It has never been fully understood why these dinosaurs had such little arms. Both T. rex and M. gigas used their enormous heads to hunt prey (SN: 10/22/18); they weren't for hunting. To avoid getting in the way during the mass feeding frenzy on carcasses, the arms may have reduced.

M. gigas' arms, however, were surprisingly muscular, suggesting that they were more than just an unwieldy appendage, according to Canale. It's possible that the arms assisted in raising the animal from a seated to a standing position. Another is that they assisted in mating, perhaps through loving their partners.