![\"Life](\"https:\/\/www.newsbeep.com\/uk\/wp-content\/uploads\/2026\/05\/image_12604-Tyrannosaurus-mcraeensis.jpg\")
<\/p>\nPaleontologists from University College London and the University of Cambridge say the large predatory dinosaurs\u2019 tiny arms evolved alongside massive heads and bone-crushing jaws, suggesting ancient predators increasingly relied on biting rather than grasping prey.<\/p>\n
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Life reconstruction of Tyrannosaurus mcraeensis. Image credit: Sergey Krasovskiy.<\/p>\n
\u201cEveryone knows Tyrannosaurus rex had tiny arms but other giant theropod dinosaurs also evolved relatively small forelimbs,\u201d said Charlie Roger Scherer, a Ph.D. student at University College London.<\/p>\n
\u201cCarnotaurus had ridiculously tiny arms, smaller than Tyrannosaurus rex.\u201d<\/p>\n
\u201cWe sought to understand what was driving this change and found a strong relationship between short arms and large, powerfully built heads.\u201d<\/p>\n
In their research, Schere and colleagues looked at data for 82 species of carnivorous theropod dinosaurs.<\/p>\n
They found that shortening of forelimbs occurred across five lineages: Abelisauridae, Carcharodontosauridae, Ceratosauridae, Megalosaurinae and Tyrannosauridae.<\/p>\n
Smaller arms were closely linked to the development of large, powerful skulls and jaws, more so than to larger overall body size, indicating that tiny arms were not just a by-product of bodies getting bigger.<\/p>\n
![\"Torvosaurus](\"https:\/\/www.newsbeep.com\/uk\/wp-content\/uploads\/2026\/05\/image_1794_1-Torvosaurus-gurneyi.jpg\")
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Torvosaurus gurneyi. Image credit: \u00a9 Sergey Krasovskiy.<\/p>\n
The researchers suggested that the increasing size of prey, in the form of gigantic sauropods and other large herbivores, may have resulted in a shift to hunting using jaws and head instead of claws.<\/p>\n
The head took over from the arms as the method of attack. It\u2019s a case of \u2018use it or lose it\u2019 \u2014 the arms are no longer useful and reduce in size over time.<\/p>\n
\u201cWhile our study identifies correlations and so cannot establish cause and effect, it is highly likely that strongly built skulls came before shorter forelimbs,\u201d Scherer said.<\/p>\n
\u201cIt would not make evolutionary sense for it to occur the other way round, and for these predators to give up their attack mechanism without having a back-up.\u201d<\/p>\n
![\"Ecosystem](\"https:\/\/www.newsbeep.com\/uk\/wp-content\/uploads\/2026\/05\/image_14522-Morrison-Formation.jpg\")
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Ecosystem reconstruction of the Late Jurassic Dry Mesa Dinosaur Quarry around 150 million years ago in Colorado, the United States. Image credit: Sergey Krasovskiy \/ Pedro Salas.<\/p>\n
For the study, the paleontologists developed a new way to quantify skull robustness, based on factors including how tightly connected the bones of the head were, the dimensions of the skull (a more compact shape is stronger than an elongated shape), and bite force.<\/p>\n
On this measure, Tyrannosaurus rex scored highest, followed by Tyrannotitan, a theropod nearly as massive as Tyrannosaurus rex who lived in what is now Argentina in the Early Cretaceous epoch, more than 30 million years earlier than Tyrannosaurus rex.<\/p>\n
\u201cIncreasingly gigantic prey may have resulted in an evolutionary arms race, where theropods developed strong skulls and jaws to better subdue this prey, and in many cases grew to gigantic sizes themselves,\u201d the researchers said.<\/p>\n