Scientists solve the mystery of T. rex's short arms

Researchers have revealed that the short arms of tyrannosaurs and other carnivorous dinosaurs shrank as their powerful skulls became the primary hunting tool.

Scraper SystemJune 30, 2026, 10:19 PM

Scientists solve the mystery of T. rex's short arms

The giant carnivorous dinosaur Tyrannosaurus rex (T. rex), which lived around 66 million years ago, is known for its disproportionately short arms despite its enormous size and bone-crushing jaws. These forelimbs, measuring only about 90 centimeters in length, were surprisingly small compared to a body exceeding 12 meters. Until now, many hypotheses had been proposed for this feature, such as grasping, attracting mates, or preventing bites while scavenging.

A new study published in the journal Proceedings of the Royal Society B offers a strong explanation to solve this mystery. Researchers from University College London and the University of Cambridge examined 82 theropod species and found a direct link between skull strength and arm shortening.

Arms shrank as the skull became a weapon

Lead author of the study, Charlie Roger Scherer, stated that they used a new metric to measure the skull's bite force, shape, and bone strength. According to this, T. rex stood out as the species with the highest skull durability, followed by the giant carnivorous Tyrannotitan, which lived in Argentina during the early Cretaceous period.

The study shows that the growth of prey —especially large herbivores like giant sauropods— over time created selective pressure on carnivorous dinosaurs. Scherer said, "As prey grew larger, dinosaurs had to develop more robust skulls and stronger jaws. Thus, the skull became the main attack organ, while the arms lost their function."

Not unique to T. rex

The research revealed that arm shortening evolved independently in at least four different theropod groups, in addition to tyrannosaurids. For example, Majungasaurus, which lived in Madagascar around 70 million years ago, had an extremely powerful skull and arms as small as those of T. rex, despite weighing only 1.6 tons. Similarly, Carnotaurus, notable for the horns above its eyes, also had exaggeratedly short arms.

In these different lineages, arm shortening occurred in different ways. In abelisaurids, the hands and lower arm shortened first, while in tyrannosaurids, all arm parts shrank proportionally. Scherer said, "In both cases, the common point is that the skull increasingly became the primary tool for catching and subduing prey."

The findings show that the short arms of giant carnivorous dinosaurs were not a flaw or an evolutionary relic, but rather the result of a major adaptation in which the skull turned into the most efficient weapon.

Scientists solve the mystery of T. rex's short arms

Researchers have revealed that the short arms of tyrannosaurs and other carnivorous dinosaurs shrank as their powerful skulls became the primary hunting tool.