T. Rex’s Tiny Arms May Have Been Vicious Weapons

SCIENCE

The tiny arms of a Tyrannosaurus rex may have been strong enough to slash prey at close quarters. (National Geographic)

What else are we learning about T. rex anatomy?

Teachers, scroll down for a quick list of key resources in our Teachers Toolkit.

A T. rex would have to hug you to hurt you with those tiny arms.
Illustration by Doug Henderson, National Geographic

Discussion Ideas

 

 

  • What evidence suggests “the arms of Tyrannosaurus rex were not functionless but adapted for vicious slashing”?
    • The author examines six of the arms’ traits.
      1. short length. The shortness of the arms would actually have been advantageous for up-close slashing.
      2. large coracoid. The T. rex’s large coracoid indicates its arms were very strong. The coracoid is part of the the bone (scapula) that stabilizes the shoulder joint and is the attachment site for muscles such as the biceps and pectorals. A T. rex’s coracoid is not only slightly longer than the leg of a six-foot man, but also of similar girth.
      3. strong arm bones. T. rex’s arm bones were quite robust and would readily have sustained the impact of slashing.
      4. powerful claws. Over time, T. rex went from three fingers to two. The unusual reduction of the number of fingers would have resulted in 50% more pressure being applied to each claw.
      5. wide range of motion. The humoral head on a T. rex’s arm was part of an unusual “quasi-ball-and-socket joint” that would have provided considerable mobility for slashing. The humoral head describes the hemispheric “ball” of the upper humerus (arm bone).
      6. big claws. T. rex’s huge sickle-shaped claws would have caused deep wounds. T. rex claws were about 8-10 centimeters (3-4 inches) long.

 

  • What are some criticisms about the new suggestion that T. rex arms were powerful weapons?
    • Those arms are just. so. tiny. “The chest is so broad on a mature T. rex, one expert noted, that the ‘effective strike zone’ of the swiping arm couldn’t be far from the animal’s torso. ‘I would expect it could cause some decent damage if it struck, but in order to deploy [the arm], Tyrannosaurus would basically have to push its chest up against the side of the victim. In such a position the tyrannosaur wouldn’t be able to use its far more powerful armament: its massively powerful jaws.’”

Unarmed: You’re staring at T. rex’s most powerful weapon, hands-down.
Illustration by Franco Tempesta, National Geographic

 

Teachers Toolkit

Nat Geo: T. Rex’s Tiny Arms May Have Been Vicious Weapons

Nat Geo: Pucker Up! New research suggests T. rex teeth were probably not protruding fangs, but kept hidden by thin, scaly lips.

Geological Society of America: EVIDENCE THAT THE ARMS OF TYRANNOSAURUS REX WERE NOT FUNCTIONLESS BUT ADAPTED FOR VICIOUS SLASHING

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