Newly Discovered Dinosaur Had Arms Smaller Than T. Rex, Raises Questions About Evolution of Abelisaurid Theropods

The Tyrannosaurus rex is known for its little arms, but as experts discover more of its relatives, the famous dinosaur species grapple with some competition.

A New Carnivorous Dinosaur Species

A study has found that a newly discovered dinosaur species had a squished, pug-like face and tiny arms. However, that did not stop it from hunting prey during the late Cretaceous period.

Dubbed as izakaya, the dinosaur was unearthed in the La Colonia Formation of central Patagonia. The details of the discovery are published in the paper "A new abelisaurid dinosaur from the end-Cretaceous of Patagonia and evolutionary rates among the Ceratosauria."

Led by paleontologist Michael Pittman from The Chinese University of Hong Kong, a team of researchers discovered the fossils of Koleken izakaya sticking out of the Patagonian desert in 2015. After excavating them for several years, the researchers recovered a partial skeleton of a single dinosaur. These include tail bones, skull bones, and near-complete legs.

The team determined that the newly found predator belonged in its own group within the Abelisauridae family. Its genus name comes from a word in the Teushen language used by the native people of central Patagonia.

"Kóleken" literally means "coming from clay and water" in the original Teushen word. Pittman and his colleagues chose this term since the fossils were found in claystone-dominated rocks from an estuarine area.

Meanwhile, the species name comes from Inakayal, the leader of the Tehuelche people who led the fight against the Argentine forces in the 19th century. Inakayal's resistance resulted in the displacement of Argentina's Conquest of the Desert military campaign from their native communities.

After identifying the dinosaur, the researchers analyzed the abelisaurid evolution, particularly on the rate at which their bodies changed compared to other dinosaur species. They discovered that this family has rapid skull evolution, which might have contributed to their success as predators.

Unique Features of Koleken Inakayali

The dinosaur is a 16-foot-long (5-meter) abelisaurid theropod that dominated the great southern landmass of Gondwana about 145 to 66 million years ago.

According to Pittman, Koleken inakayal were the apex predators in modern-day Argentina. This means that they occupied the same role that T. rex would have been doing in some areas of ancient North America.

Abelisaurids had a similar body plan to a T. rex, including stunted arms and bulky hind limbs. However, the skull of the newly discovered dinosaur was found to be much flatter than those of its family members. In terms of dog breeds, it can be compared to a pug, according to Pittman.

The apex predator lived with another abelisaurid named Carnotaurus sastrei. This dinosaur species had notable horns and was found in 1985 in the same geological formation.

Meanwhile, Koleken inakayal did not have horns, a feature used by researchers to distinguish its skeleton from Carnotaurus sastrei and other members of the Abelisauridae family. According to the Natural History Museum in London, K. izakaya was also smaller than C. sastra, which measured 26 feet (8 meters).