For over a century, the purpose of Tyrannosaurus rex's disproportionately small arms has baffled palaeontologists. First discovered in 1902 by Barnum Brown in Montana's Badlands, the iconic dinosaur's forelimbs measured just 3ft (0.9m) on a 45ft (13.7m) individual, sparking intense speculation that continues today.
Brown's initial find, the first T. rex ever unearthed, lacked fingers and forearms. Early portraits used guesswork, but later complete skeletons confirmed the arms were genuinely stunted. 'You can look at his arms and say, well, these are ridiculous,' says L J Krumenacker, a palaeontologist at Idaho State University. 'They're so different than anything around today, what is the point?'
Despite decades of study, no consensus has emerged. Theories range from grasping prey to aiding mating, but none have been proven. Some scientists speculate that if T. rex had survived the mass extinction 66 million years ago, it might have eventually lost its arms altogether, as they became redundant for hunting—the head taking over that role entirely.
The mystery endures, making T. rex as famous for its puny arms as for its massive teeth. 'There is no question but what this is the find of the season so far for scientific importance,' Brown wrote to his boss Henry Fairfield Osborn in 1902, unaware that the arms would remain an enigma for 120 years and counting.
