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Why Did the T. Rex Have Such Short Arms?

Updated May 17, 2024
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The Tyrannosaurus rex was a vicious and terrifying dinosaur of the late Cretaceous period. The “King of the Tyrant Lizards” stood up to 12 feet tall and 40 feet long. A fearsome predator that could weigh more than eight tons, it had the strongest bite of any animal on Earth. With a mouth containing 60 saw-like teeth, the T. rex could exert up to six tons of pressure with a single bite. It was a menacing creature to be sure, except for one notable feature: its short arms. The T. rex wasn’t the only dinosaur with this odd trait, as many of its theropod cousins had the same issue.

Scientists aren’t entirely sure why the T. rex and other theropods had such short arms, but they do have theories. Kevin Padian, a paleontologist at the University of California, Berkeley, hypothesizes that the arms of the T. rex were originally longer, but shortened over time to prevent accidental amputation during a feeding frenzy. In a fresh kill scenario, it wouldn’t have been beneficial for the massive dinosaur to have long, loose limbs that could be torn up as well. Another theory is that the short arms were for mating purposes, used to grab and hold onto a female during mating.

Other proposed explanations for why theropods had such short arms include that they were useful as anchors to lift themselves up off the ground, or for holding down prey. Steven Stanley, a paleontologist at the University of Hawai'i at Mānoa, believes that the short arms were useful for slashing prey in close proximity. More ideas will certainly emerge over time, but so far, scientists have been unable to prove any of the theories with absolute certainty.

Tracking the T. rex:

  • American paleontologist Barnum Brown dug up the first full Tyrannosaurus rex skeleton in 1904.

  • Despite only being around three feet long, studies have shown that a T. rex’s arms were capable of bench pressing up to 400 pounds.

  • The arms of a T. rex had a limited range of movement. They were only capable of swinging across at an angle of approximately 45 degrees.

WiseGeek is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
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