Why not come face to face with the world’s most fearless dinosaur? Insult it where its insecurities lie: in its tiny little arms.
Scientists have long agreed that human limbs are small; the tyrannosaurus rex had them totally useless. However, the actual evolutionary trigger behind their size is still up for debate. Thanks to new research, we may finally have an answer.
Researchers from University College London (UCL) and the University of Cambridge studied 82 species of theropods—two-legged, predominantly carnivorous dinosaurs. They found that as the head and jaw of the tyrannosaurus grew larger, the arms began to shrink.
This means the tyrannosaurus and other predatory dinosaurs evolved to use their heads and jaws as their primary attack weapons rather than their claws. Consequently, their arms became less utilized and diminished over time, leading to the tiny arms we joke about today.
Researchers have known for a long time that while the arms of the tyrannosaurus rex are vestigial—they have lost most, if not all, of their original function through evolution—this new link between arm reduction and head expansion presents a novel insight.
A study published in the journal Proceedings of the Royal Society B found that smaller arms were more closely related to the development of large, powerful skulls and jaws than to the dinosaur’s overall body size. It’s not merely because the tyrannosaurus was bigger.
“The head replaced the arm as a method of attack,” explains lead author Charlie Roger Scherer, a PhD student in UCL Earth Sciences. “It’s a ‘use it or lose it’ problem. The arm is no longer useful and will decrease in size over time.”
“These adaptations often occurred in areas with large prey. Trying to grab a 100-foot-long sauropod with your claws isn’t ideal; using your jaws might be more effective.”
While small arms are commonly associated with the tyrannosaurus, there were plenty of other theropods that also skipped arm days. Scheller notes that the Carnotaurus had even smaller arms than the tyrannosaurus.
Interestingly, the dinosaur’s overall size doesn’t seem to determine arm size. Despite being a fraction of the size of the tyrannosaurus, some smaller theropods possessed similarly powerful heads and tiny arms.
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Source: www.sciencefocus.com