Were the Tiny Arms of the T. Rex Actually Useless?

Almost everything about the Tyrannosaurus rex says "ferocious," especially its 4-foot (1.2-meter) long jaw, designed for efficient bone-crushing, and its serrated teeth, likely used to grip and rip the flesh of its prey. But according to widespread belief, the T. rex's two-fingered, 3-foot (.9 m) long forearms, seemed pretty useless, and were certainly too short to reach the Tyrannosaurus rex's mouth. However, Steven Stanley, a paleontologist at the University of Hawaii, would disagree about those arms being so useless. His 2017 research suggests that the dinosaur’s arms were well-suited for “vicious slashing,” ending in four-inch (10 cm) claws that could open up deep wounds during close combat.

Short-armed and dangerous:

• Over the years, scientists have argued that the T. rex’s small arms were only used to help resting dinosaurs push themselves up from the ground, or to grasp mates during copulation.
• Stanley theorizes that the T. rex's shoulder joint, unusual for dinosaurs of its type, was almost a ball-and-socket joint that would facilitate a free-swinging mobility needed to slash prey.
• Other paleontologists aren’t convinced. The T. rex's short arms would mean that “the Tyrannosaurus would basically have to push its chest up against the side of the victim,” one argued.

Frequently Asked Questions

What purpose did the T. Rex's tiny arms serve?

Contrary to popular belief, the T. Rex's arms were quite muscular and may have been used for specific tasks. According to research, their robust bone structure and considerable muscle attachment suggest they could have been employed for slashing prey, aiding in mating rituals, or helping the dinosaur to rise from a prone position.

How strong were the T. Rex's arms?

The T. Rex's arms, despite their size, were incredibly strong. Studies estimate that they could lift approximately 400 pounds (181 kilograms). The bicep alone could likely curl over 430 pounds (195 kilograms), indicating that their strength was considerable and their arms were far from useless.

Could the T. Rex's arms reach its mouth?

No, the T. Rex's arms were too short to reach its mouth. This limitation has led to speculation about their function since they couldn't have been used to feed themselves. However, their strength suggests they had other uses that did not require such reach, like grasping during mating or manipulating prey.

Did the T. Rex's arms evolve over time?

Yes, the arms of the T. Rex did evolve over time. Paleontological evidence suggests that the ancestors of T. Rex had longer arms, and over millions of years, these limbs became shorter and more robust. This evolutionary change implies that the arms still had a function, which natural selection refined for specific purposes.

How did the size of the T. Rex's arms compare to other dinosaurs?

The T. Rex's arms were proportionally shorter compared to many other theropod dinosaurs. While some relatives also had short arms, the T. Rex's were notably smaller relative to its massive body size. This unique trait has puzzled scientists and led to various theories about their potential use and evolutionary advantage.

Are there any modern animals with similar limb proportions to the T. Rex?

Modern animals with similar disproportionate limb sizes are rare, but some species exhibit reduced limbs for specific evolutionary advantages. For example, certain types of burrowing frogs have tiny limbs compared to their bodies, which aid in their underground lifestyle. However, no modern animals show a disparity as pronounced as the T. Rex's arms to body size ratio.