Found: T. Rex’s Ancient Cousin Meraxes Gigas

There’s a new dinosaur species on the block. Discovered in Argentina’s Patagonian Desert, the new guy looks a lot like a Tyrannosaurus rex but is only a distant cousin to the classic predator. 

Like T. rex, the newcomer had a massive head and puny arms. It was from a class of dinos called carcharodontosaurids, which grew to be 36 feet long or so and was likely at or near the top of the food chain in their time. The new monster was named Meraxes gigas, after one of the dragons from “Game of Thrones.”

The new specimen of carcharodontosaurid is the most complete fossil of its kind found in the Southern Hemisphere. These beasts lived and died some 150 million to 90 million years ago. 

M. gigas is now the third species of extinct reptilian predators with the curious morphology of big head, little arms. These cartoonish creatures evolved separately – M. gigas, for example, was extinct for 20 million years before T. rex appeared on the scene.

There are competing theories as to why (or how) this body type evolved. One holds that the little limbs were more involved with reproduction or balance than feeding, so big arms were not necessary. Another, which the new discovery seems to support, is that, over the expanse of time and relentless natural selection, the creature’s head grew and the arms became less necessary.

The research appears in the journal Current Biology.

Photo credit: Carlos Papoli via science.org