December 30 , 2016:

by Sarah Gibson

The study, led by authors Sebastián Apesteguía (Universidad Maimónides in Argentina), Nathan D. Smith (the Dinosaur Institute at the Natural History Museum of Los Angeles County), Rubén Juárez Valieri (the Gobierno de la Provincia de Río Negro in Argentina), and Peter J. Makovicky (The Field Museum), describes a unusual theropod dinosaur with two-fingered hands, similar to Tyrannosaurus rex. However, Gualicho is more closely related to allosaurids, indicating that didactyl hands had evolved independently on multiple branches of the theropod family tree.

“Gualicho is kind of a mosaic dinosaur, it has features that you normally see in different kinds of theropods,” says author Peter Makovicky. “It’s really unusual—it’s different from the other carnivorous dinosaurs found in the same rock formation, and it doesn’t fit neatly into any category.”

The forelimbs are the size of human arms, despite the dinosaur being large. The researchers in this study estimate Gualicho weighed about 1,000 pounds. And Gualicho‘s unusual limbs adds evidence that the trait evolved independently numerous times. “By learning more about how reduced forelimbs evolved, we may be able to figure out why they evolved,” explained Makovicky.

Phylogenetically, the study recovers Gualicho as closely related to Deltadromeus, an African neovenatorid charcarodontosaurian. Indeed, the two taxa share many derived characters in the scapula, femur, and humerus. The study recovered Gualicho as a neovenatorid, thus making it the first representative of this clade in the region. Additionally, this study highlights that Gualicho is the most basal taxon in this area of the tree to evolve the digit reduction more commonly associated with tyrannosaurs and other tetanurans.

Akiko Shinya described the moment when she found Gualicho, “We found Gualicho at the very end of the expedition. Pete joked, ‘It’s the last day, you’d better find something good!’ And then I almost immediately was like, ‘Pete, I found something.’ I could tell right away that it was good.”

And it was very good indeed. So good that the Paleontology Community voted Gualicho as the number 1 pick for the Fossil Vertebrate published in an Open Access Journal for the past year. Congratulations to Gualicho, and to all of the team involved in this great find!

We at PLOS Paleo wish you all of the best for the new year! Thank you to everyone who reads, contributes, researches, and inspires all of the awesome research in the community!

Reference:

Apesteguía S, Smith ND, Juárez Valieri R, Makovicky PJ (2016) An Unusual New Theropod with a Didactyl Manus from the Upper Cretaceous of Patagonia, Argentina. PLoS ONE 11(7): e0157793. doi:10.1371/journal.pone.0157793