Okay, I have to admit that this next story isn’t strictly Earth Science, and it really is not space science, but since dinosaurs were eventually killed off by a meteor, and we just like dinosaurs, we are going to sneak some dinosaur science into this show.

Most of us are familiar with the tiny armed Tyrannosaurus rex. At some point, probably around age five or six, I think many of us have asked, “How did a dinosaur with such a large head and tiny arms get back up if it fell over? Why would evolution create such a bizarre arm-to-leg-to-head ratio?”

T. rex is just one of a small handful of these weirdly structured carnivores that include the Giganotosaurus that was in Jurassic Park, and there is the newly discovered Meraxes gigas. It is this newly discovered Meraxes that may allow us to finally make sense of these giant feathered beasts. 

Discovered in Patagonia in 2012 and slowly extracted and analyzed, this dino’s 90-95 million-year-old skeleton is one of the most complete found in the Southern Hemisphere. According to Peter Makovicky: The neat thing is that we found the body plan is surprisingly similar to tyrannosaurs like T. rex, But, they’re not particularly closely related to T. rex. They’re from very different branches of the meat-eating dinosaur family tree. So, having this new discovery allowed us to probe the question of, ‘Why do these meat-eating dinosaurs get so big and have these dinky little arms?’

Makovicky and his team’s work is published in a new paper in Current Biology where they describe how the discovery of multiple skeletons that show convergent evolution on this tiny arms-giant head structure hints at why this could happen. As Makovicky explains: We shouldn’t worry so much about what the arms are being used for, because the arms are actually being reduced as a consequence of the skulls becoming massive. Whatever the arms may or may not have been used for, they’re taking on a secondary function since the skull is being optimized to handle larger prey.

Put another way, evolution said, “Sure, you can have a bigger head to kill bigger things, but imma take your arms and make them tiny.”

And now you know.

More Information

University of Minnesota press release

“New giant carnivorous dinosaur reveals convergent evolutionary trends in theropod arm reduction,” Juan I. Canale et al., 2022 July 7, Current Biology