An article published in the journal PLOS ONE describes the discovery of a theropod dinosaur that was called Gualicho shinyae. It’s been classified in the group of carnosaurs and what makes it particularly interesting is that its arms are small like those of the more famous Tyrannosaurus rex, classified in another group of theropods. This suggests that this feature evolved a number of times independently.
A partial skeleton of Gualicho shinyae was discovered in Patagonia, Argentina, in 2007, but only this year it was described and received a name. As often happens, the researchers had to conduct a study based on only a few bones of a single specimen, and this forced them to resort to various estimates of this species of dinosaur.
According to these estimates, Gualicho shinyae was a medium size carnosaur with a weight of around half a ton, comparable to that of a polar bear. The specimen was discovered in a formation dating back about 93 million years ago, during the Cretaceous period. Carnosaurs (Carnosauria) were predators with physical characteristics such as teeth, neck muscles and jaws that showed a series of adaptations to hunting, even large prey.
Generally, carnosaurs arms ended with three fingers but those of Gualicho shinyae have only two of them. Moreover those are really short arms, just like those of T. rex, which however is its distant relative. This means that during the evolution of both species, the arms got shorter independently.
It’s not clear why in some theropod arms atrophied and perhaps the discovery of the Gualicho shinyae won’t clarify the mystery. However, the fact that this happened in theropods of different families, even if rarely, suggests that in certain cases there were particular evolutionary pressures.
Gualicho shinyae also has other features that make it similar to other theropods. The classification of many species is controversial because the relations are difficult to understand when they have so many partial skeletons. For example, the relation between Megaraptora grup and the coelurosaurs (coelurosauria) group is a source of a lot of controversy.
Even on the classification of Gualicho shinyae a dispute already started because similarities were noticed between its caudal vertebrae and those of Aoniraptor libertatem, another dinosaur classified in the Megaraptora group again discovered in Argentina, dating back to the late Cretaceous. What’s more, there’s a dispute as to the validity of the assignment of the name Aoniraptor libertatem so the issue is all to see.
All these disputes are a symptom of the difficulties paleontologists face in the reconstruction of various groups of animals, in this case of theropod dinosaurs. That’s why every new discovery is important in research. Gualicho shinyae is a species of particular interest for its characteristics so the bones found will surely keep on being studied.
