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Meet Guemesia ochoai, New Abelisaurid Dinosaur from Argentina


A new genus and species of abelisaurid theropod has been identified from a partially complete skull found in northwestern Argentina.

An artist’s reconstruction of Carnotaurus sastrei, an abelisaurid theropod that lived in South America during the Late Cretaceous epoch, sometime between 72 and 70 million years ago. Image credit: Jake Baardse.

An artist’s reconstruction of Carnotaurus sastrei, an abelisaurid theropod that lived in South America during the Late Cretaceous epoch, sometime between 72 and 70 million years ago. Image credit: Jake Baardse.

The newly-identified dino species lived approximately 70 million years ago during the Early Creataceous epoch.

Scientifically named Guemesia ochoai, the ancient beast was a type of abelisaurid.

“The fossil record of abelisaurid theropods in South America is mostly limited to Brazil and Argentina,” said lead author Dr. Federico Agnolín, a paleontologist at the Museo Argentino de Ciencias Naturales ‘Bernardino Rivadavia’ and CONICET, and his colleagues.

“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for northwestern Argentina, abelisaurids are represented by incomplete and isolated bones and teeth that remain largely unpublished.”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 paleontologists found a nearly complete braincase — including the upper and back parts of the skull — of Guemesia ochoai in reddish sandy siltstones of the Los Blanquitos Formation that crop out in the south part of the Amblayo valley, close to Amblayo town, in Argentina’s Salta province.

The specimen had typical abelisaurid features: a thin skull roof, absence of skull projections like horns or bulges, and low and narrow parietal eminence at the same level as the sagittal crest.

“It shows a unique combination of characters, including striking plesiomorphic features for an abelisaurid, such as dorsoventrally thin frontal bones and a narrow and relatively low parietal eminence,” the researchers said.

“It also has a unique set of internal cavities within the frontals that communicate with the dorsal surface, perhaps implying a pneumatic and vascular origin.”

“Further, as inferred from preserved elements, Guemesia ochoai is a relatively small taxon, much smaller than derived abelisaurids such as Abelisaurus and Carnotaurus.”

Braincase of Guemesia ochoai. Scale bar - 5 cm. Image credit: Javier Ochoa.

Braincase of Guemesia ochoai. Scale bar – 5 cm. Image credit: Javier Ochoa.

During the Late Cretaceous epoch, South America was divided into northeastern and southwestern realms by a sea corridor which acted as a filter for some vertebrates.

The strong morphological differences exhibited by Guemesia ochoai in contrast to other abelisaurid dinosaurs may be an additional proof of the biogeographic distinctiveness of northwestern Argentina during the Late Cretaceous.

Guemesia ochoai is quite unusual for its kind,” said co-author Professor Anjali Goswami, a paleontologist at the Natural History Museum, London.

“It has several key characteristics that suggest that is a new species, providing important new information about an area of the world which we don’t know a lot about.”

“It shows that the dinosaurs that live in this region were quite different from those in other parts of Argentina, supporting the idea of distinct provinces in the Cretaceous of South America.”

“It also shows us that there is lot more to be discovered in these areas that get less attention than some of the more famous fossil sites.”

The findings were published in the Journal of Vertebrate Paleontology.

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Federico L. Agnolín et al. First definitive abelisaurid theropod from the Late Cretaceous of northwestern Argentina. Journal of Vertebrate Paleontology, published online February 10, 2022; doi: 10.1080/02724634.2021.2002348



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