An unusual raptor dinosaur found in Argentina is the largest of its kind found so far in the Southern Hemisphere, with awkwardly short arms that made it resemble a Tyrannosaurus, researchers reported.

The creature would have weighed 368 kg and been nearly 5 meters long when it hunted in what is now Patagonia 100 million to 65 million years ago, the researchers said.

The discovery sheds light on the evolution of dromaeosaurids, birdlike dinosaurs that ran on two legs and are considered by many to have been the most intelligent of the dinosaurs.

Fernando Novas of the Museo Argentino des Ciencias Naturales and colleagues named the newly discovered species Austroraptor cabazai -- from austral in reference to southern South America, and raptor meaning thief. The cabazai honors the late Alberto Cabaza, founder of the Museo Municipal de Lamarque, whose researchers also helped in the work.

Raptors or dromaeosaurids were slender two-legged hunters popularised in fictional books and films such as Jurassic Park in part because of their sharp claws.

Novas' team called theirs a "a startling new example" of the species because of its size, long snout and short arms. The animals usually had long forearms, they said.

By the time an impact from space sent the dinosaurs into extinction 65 million years ago, the group would have included animals ranging from crow-sized winged creatures to giants such as A. cabazai, they said.