Argentine dinosaur might have been armless but surely not harmless

With front arms so small that even T. rex could make fun of.
Ameya Paleja

A team of paleontologists in Argentina has recently published their findings of a new but armless species of dinosaur called Guemesia ochoai. Prior to their extinction, 66 million years ago, these dinosaurs are believed to have roamed across Europe, Africa, South America, and India.  

Paleontologists are always looking deep into our past to understand how we evolved into what we are today. While recent human fossils not more than 2,500 years old can provide details of what diets people consumed, with older fossils they can go further back in history to even pinpoint when species evolved into new ones. The recent finding sheds more light on a species called Abelisuarids, a therapod or dinosaur with hollow bones. 

Abelisuarids were biped dinosaurs with stocky hind limbs with three functional digits. These dinosaurs were quite large in size with estimates suggesting that they were up to 39 feet (12 m) long, however, the recent study reports one of the smallest abelisaurids reported to date. 

Guemesia ochoai is as mean as T. rex

The estimates have been made from an almost complete braincase found for the dinosaur in the Amblayo Valley, Salta province in Argentina. The braincase shows a thin skull roof and absence of horns, the researchers write in their research paper. While these characters are characteristic of abelisaurids they aren't unique to them either. 

For their large bodies, G. ochoai, had very small arms. Researchers believe these arms are the vestigial remnants of arms that once benefitted the dinosaurs' ancestors but were no longer functionally useful to them. Like other dinosaurs in its category, G. ochoai could not bend their upper limbs and not even have claws Even with namesake arms, G. ochoai is believed to have been nasty carnivores, taking down their prey with ease. 

But more importantly, the presence of the fossil confirms that even within Abelisaurids found in Argentina, there were geographic distinctions. While previous Abelisaurids have been found in the country's southern Patagonian region, G. ochoai was found in the northwest, opening an abundance of possibilities of what the region might hold clues to. 

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Adding to the mystery is the fact that fossilized remains from Argentina have remained rather unexplored. So, this might be the first you might have heard about abelisaurids but is unlikely to be the last.  

The findings were published in the Journal of Vertebrate Paleontology.

Study abstract:

The fossil record of abelisaurid theropods in South America is mostly limited to Brazil and Argentina. In Argentina, abelisaurids are generally known from Patagonia, where their record is relatively abundant and includes well-known and complete specimens. However, for Northwestern Argentina, abelisaurids are represented by incomplete and isolated bones and teeth that remain largely unpublished. The aim of this contribution is to report a nearly complete abelisaurid braincase from the Late Cretaceous Los Blanquitos Formation (Campanian), Amblayo Valley, Salta province, Argentina. The specimen shows plesiomorphic features for abelisaurids, including a thin skull roof, absence of skull projections like horns or bulges, and low and narrow parietal eminence that lie at the same level as the sagittal crest. Furthermore, the specimen possesses some autapomorphies that support its status as a new taxon and its small size allows it to be assigned as one of the smallest abelisaurids recorded up to date. The finding of this specimen constitutes the first unequivocal occurrence of an abelisaurid in Northwestern Argentina and brings new evidence concerning the geographic distribution of the clade during the Late Cretaceous times in South America. 

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