Question Your World: Why Do Some Dinosaurs Have Dinky Arms?

Posted: February 27, 2022

A team of researchers just discovered a brand new species of dinosaur, Guemesia ochaoi. It’s a member of the Abelisaurid family of dinosaurs, the ones with kind of dinky arms. And according to these scientists, dino arms don’t get much dinkier than this particular discovery. Imagine a semi T. rex-looking creature but with even smaller arms flapping around as it runs around! 

This particular dinosaur would have been around about 70 million years ago in the late Cretaceous Period, a few million years before the T. rex. With that said, these two animals are not very closely related. Guemesia and T. rex are related about as much as humans are to bats. 

So, if these animals are not related, why do they both have tiny arms? Hey, maybe the arms just didn’t matter as much to them folks! In order to survive, dinosaurs had to essentially be successful at eating and mating. You don’t necessarily need arms to do that. Don’t get us wrong, it helps, but it's not necessary. While Guemesia may not have had big arms, it certainly was armed … with a very powerful jaw and razor-sharp teeth to catch prey and defend itself. 

With successful traits in place, over millions of years some unnecessary physical features can get smaller or go away altogether. For example, in dark caves where there is little or no light, there are fish that have evolved over millions of years that have no eyes. They use other senses to navigate their world. Just like the Abelisaurid arms, this fish has lost a body part that no longer helps them survive. If they don’t need it, then why expend the energy into that body part? 

Vestigial body parts can be found throughout the animal kingdom. In fact, some whales still have tiny legs under all that blubber! Even humans are in this club thanks to our appendix. 

This new discovery now adds more knowledge to the greater understanding of the dinosaur family tree. This is one of the many recent discoveries to come from Argentina, an area that has not been explored as much and is considered a hot spot for future dino discoveries. 

For the time being though it’s nice to know that by learning about dinosaurs with small arms we put more prehistoric knowledge within reach.