Koleken dinosaur: Newly discovered dino had arms so small it makes the T-rex 'look like a bodybuilder'

Researchers have discovered a brand new species of dinosaur with an unusual attribute - arms so tiny it makes the famously short-armed T-rex look like a bodybuilder.

The newly discovered Koleken inakayali is thought to have lived during the Late Cretaceous period, some 70 million years ago, in what is now South America. It was discovered by National Geographic explorer Diego Pol, alongside international researchers and palaeontologists working in Central Patagonia’s La Colonia Formation.

The team, whose findings were published this week in science journal Cladistics, unearthed a partial skeleton, - including several skull bones, an almost complete series of back bones, a hip, several tail bones, and near-complete legs. The Koleken is part of a family of carnivorous dinosaurs known as abelisaurids, the researchers say, and it resembles its only known relative to live in roughly the same time and place - the ‘meat bull’, or Carnotaurus - of Jurassic World fame.

The Koleken, however, is smaller in size, they say, and is missing the massive frontal ‘horns’ possessed by Carnotaurs. The new dinosaur's name is derived from the language of the region’s Tehuelche people, and refers to both the claystone the animal was found in, and Tehuelche leader Inakayal.

It also appeared to have particularly tiny arms, of which the exact purpose was unclear. Many abelisaurid dinosaurs, including the much more well-known Tyrannosaurus rex, were known to have short arms. Palaeontologists have a number of theories, including that they evolved shorter arms to prevent them accidentally being bitten off when a pack of sharp-toothed predators descended on a kill - or that they were waved around to attract mates.

The Koleken also appeared to have co-existed with another recently discovered dinosaur, the Titanomachya gimenezi - the smallest known member of the Titanosaur family.

Explorer Diego Pol said the new finding shed some light on the types of abelisaurid dinosaurs who lived in Patagonia right before the mass extinction event. “Our study also analyses the evolution of abelisaurids and their relatives through time, and identifies pulses of accelerated rates of skull evolution in the Early Cretaceous. It expands what we know about abelisaurids living in this area during the Cretaceous Period and shows that they were more diverse than previously understood.”

National Geographic Society chief science and innovation officer, Ian Miller, added: “The discovery of Koleken inakayali significantly furthers our collective scientific understanding of the dinosaur era. The addition of Koleken inakayali to the La Colonia Formation fauna continues to demonstrate that the Formation is amongst the most important end-Cretaceous dinosaur-bearing rock units in the world.

“Diego and his team of global experts, researchers and lab technicians are bringing to life new insights about this lost world and furthering the National Geographic Society’s work to engage in science and exploration to better understand the wonder of our world and share those findings with the global community,” he continued.