Murusraptor barrosaensis likely a megaraptorid "Giant Thief"

A new species of megaraptorid dinosaur discovered in Sierra Barrosa in northwest Patagonia may help discern the evolutionary origins of the megaraptorid group, according to a study published in the open-access journal PLOS ONE by Philip Currie from the University of Alberta and Rodolfo Coria from the Consejo Nacional de Investigaciones Científicas y Técnicas in Argentina.

"This is a super-cool specimen from a very enigmatic family of big dinosaurs," says Currie, University of Alberta professor and Canada Research Chair in Paleobiology. "Because we have most of the skeleton in a single entity, it really helps consolidate their relationships to other animals." Currie says it is likely that this family of dinosaurs has relationships to other dinosaurs on other continents as well. The finding represents one of the most complete megaraptorids ever found, with an unusually intact braincase and distinctive facial features not previously seen among megaraptorids. "It's the only known braincase material we have of any megaraptor."

The South American Drumheller

One of the world's most renowned vertebrate paleontologists, Currie has been conducting fieldwork in Argentina for the past two decades. He and his Argentinian colleague Coria found the specimen in the year 2000 in Sierra Barrosa, near the town of Plaza Huincul, the South American equivalent of Drumheller. "It's a small place with lots of dinosaurs around," says Currie. "Probably half of the South American dinosaurs are within 200 kilometres of the town."

Currie, Coria, and their crew found the theropod skeleton on a vertical cliff in what Currie describes as a technically difficult excavation. The strenuous fieldwork certainly delivered a huge payoff for the paleontologists. "It was very evident that it was a beautifully preserved specimen of pure white in red rock. The hips were really interesting because they are pneumatic, clearly air-filled, not the kind of thing you expect to see in a big theropod." Currie says this animal, not yet an adult, was roughly eight metres long when alive-and was still growing.

The Patagonian region of Argentina has proven to be rich in fossils from the Late Cretaceous epoch, including a number of megaraptorids, a clade whose carnivorous diet gave rise to their name meaning "giant thieves." These medium-sized theropod dinosaurs, including South American genera Megaraptor, Orkoraptor and Aerosteon as well as genera from Australia and Japan, have characteristically large claws and air-filled, birdlike bones.

"A lot of people have been waiting for this paper," says Currie. "When you have most of the skeleton, it takes a long time to do all the work on it. It turns out this animal is related to Megaraptor, found only 30 kilometres away in a different rock formation. The upshot was the more we looked, we could test whether Megaraptor was a dromaeosaur, which it isn't in the strict sense, and what was thought to be the foot claws-the big can-opener claw of a dromaeosaur or raptor-were actually from the hands. We discovered all sorts of things through the course of our research."