Why the T. rex had teeny tiny arms

New paleontological research has discovered the reason why the Tyrannosaurus Rex didn't need bigger arms.

Michelle Starr Science editor
Michelle Starr is CNET's science editor, and she hopes to get you as enthralled with the wonders of the universe as she is. When she's not daydreaming about flying through space, she's daydreaming about bats.
Michelle Starr
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(Credit: Tyrannosaurus rex image by Julian Fong, CC BY-SA 2.0)

New paleontological research has discovered the reason why the Tyrannosaurus rex didn't need bigger arms.

The Tyrannosaurus rex was a fearsome apex predator during its day, and it looked the part. Except for its rather goofy-looking tiny arms, which — in comparison to the rest of the beast's mighty, 12-metre body — seem pretty useless.

Recent research suggests that dinosaurs have more in common with birds than reptiles, which could be the case with the T. rex; look at a chicken without feathers and its wings look just as strange as a T. rex's arms. This avian relationship could explain why the T. rex does have such tiny, almost vestigial arms: because, like a bird, it relied on its very strong and powerful neck muscles.

A team of researchers led by Eric Snively of the University of Wisconsin–La Crosse made a study of birds to determine how tyrannosaurs made their kills. The neck muscles of the dinosaurs are very similar to the neck muscles of modern birds, which use their heads and necks — rather than their forelimbs — to hunt and feed.

Equipped with this knowledge, the team studied 10 different species of birds, from chickens to eagles, attaching electrodes to their necks to study the precise muscle movements the birds make when feeding.

"We looked at a number of raptors and documented their behaviour," Snively told New Scientist. "There is a strong possibility that the tyrannosaurs behaved in the same way."

Birds fix their sight on their prey before thrusting forward to attack, then raise their heads upwards and pulling backwards with its legs to swallow. Some of them also shake their heads — a movement, Snively said, could be used to shake meat free from a carcass. All these muscles were present in the necks of tyrannosaurs.

"Tyrannosaurs didn't need big arms to hunt, because their powerful bites and hyper-bulldog necks did the job," Snively said. "From the shoulders forward, T. rex was like a whole killer whale: just bite, shake and twist."

The full research paper, "The role of the neck in the feeding behaviour of the Tyrannosauridae: inference based on kinematics and muscle function of extant avians", can be found online from the Journal of Zoology.

Via www.newscientist.com