For dinos like T. rex, puny arms may have been the price of a giant head

Science.org has a story about the discovery of a new theropod dinosaur.  This one is called Meraxes gigas, after a Targaryen dragon from Game of Thrones.  It lived about 95 million years ago in what is now the Patagonian Desert of Argentina.  It belonged to a family of theropod dinosaurs called Carcharodontosauridae.  All the details can be found in a paper in the journal Cell Current Biology.

In the rolling hills of Argentina’s Patagonian Desert, Juan Canale struck paleontological gold. Within half the length of a soccer pitch, his team discovered five dinosaur skeletons, including a new species that’s a Tyrannosaurus rex doppelgänger—the third known giant dinosaur to evolve stubby arms and cartoonishly large heads. In a new study, Canale’s team suggests the forelimbs shrank as a consequence of skull growth, not for any function of their own.

“The fact that you see it over and over again in parallel does suggest that there might be a common driver,” says Matthew Carrano, curator of dinosaurs at the Smithsonian’s National Museum of Natural History, who wasn’t involved with the study.

The new species is a carcharodontosaurid—an 11-meter-long dinosaur that went extinct 20 million years before T. rex lived and is only distantly related to it. Despite the evolutionary distance, scientists suspected they shared a similar body plan, but couldn’t know for sure because the preserved fossils were fragmentary; small forelimb segments are rare in the fossil record. The new discovery was a “lucky strike,” says Canale of the Ernesto Bachmann Paleontological Museum, and lead author of the study.

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