Fearsome Dinosaur With Ludicrously Tiny Arms Means T. Rex Wasn't Alone

Artists' impression of two G. shinyae hunting down their prey. Jorge González and Pablo Lara

This new fossil discovery adds credence to the idea that there was some sort of evolutionary pressure on large carnivorous theropods to reduce their arm length. When creatures evolve, if they gain a new morphological advantage they have to normally lose something else from their body plan – new features cannot simply keep adding to the original.

When human ancestors began to evolve larger brains, for example, they also lost a lot of muscle mass at the same time. The same idea applies to these carnivorous beasts – by losing any useful arms, they may have gained something elsewhere, perhaps increased muscle mass in their legs. In any case, there appeared to be no real practical use for their arms, as they were perfectly adapted to hunting down their prey without them.

“By learning more about how reduced forelimbs evolved, we may be able to figure out why they evolved,” Makovicky added.

The genus of G. shinyae is named after Gualichu, a spirit revered by Patagonia’s Tehuelche people. The team of paleontologists decided to name their fossilized monster after it after they joked about the string of bad luck, which they dubbed the “curse of Gualichu”, that befell them during their expedition. In one particular incident, their truck hit a severe bump in the road and rolled over – although no-one was injured, at least.

The curse strikes again. Credit: Pete Makovicky

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