Bizarre new species of dinosaur discovered in Argentina

Guemesia ochoai could have resembled relatives such as Carnotaurus sastrei (pictured). Credit: © Fred Wierum, under CC BY-SA 4.0 license via Wikimedia Commons

A new dinosaur among an array of “unusual” creatures has been discovered in Argentina.

The new species Guemesia ochoaimay be the close relative of the ancestors of a group of armless dinosaurs, which roamed the southern hemisphere more than 70 million years ago.

A partially complete skull discovered in Argentina provides new evidence of a unique ecosystem during the late Cretaceous.

Guemesia ochoai was a species of abelisaurid, a clade of carnivores that roamed what is now Africa, South America, and India. Dating back around 70 million years, the dinosaur may have been a close relative of the ancestors of the entire group.

The discovery of Guemesia ochoaiThe skull offers valuable insight into a region that has very few abelisaurid fossils, and may partly explain why the region gave rise to such unusual animals.

Professor Anjali Goswami, head of research at the museum and co-author, says: ‘This new dinosaur is quite unusual for its species. It has several key features that suggest it is a new species, providing important new information about a region of the world that we know little about.

“This shows that the dinosaurs that lived 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 much more to discover in these areas that receive less attention than some of the more famous fossil sites.

The description of the dinosaur, carried out by Argentinian researchers, was published in the Journal of Vertebrate Paleontology.


Abelisaurs had very reduced forelimbs, shorter even than those of Tyrannosaurus rex. Credit: © Kabacchi, licensed under CC BY 2.0

Armless, but not harmless

Hundreds of millions of years ago, all the continents were united in a supercontinent called Pangea. Over time, as the tectonic plates moved, this landmass began to move into Gondwana and Laurasia.

180 million years ago, these two massive continents would begin to separate themselves, with Gondwana breaks up to form the main continents of the southern hemisphere, as well as India.

As the new continents slowly moved apart, species could still have moved between them, leading some scientists to suggest that the fauna of each landmass would have remained. largely the same.

One of the groups living in Gondwana at the time was the abelisaurid dinosaurs. They were a group of top predatory theropods that possibly fed on large dinosaurs such as titanosaurs. Yet, despite this fearsome way of life, they managed to bring down their enormous prey without the use of weapons.

Many species of abelisaurs had even shorter forelimbs than those of the more famous tyrannosaurus rex and actually useless. This would have left abelisaurids’ hands unable to grasp, forcing the dinosaurs to rely on their heads and powerful jaws to capture prey.

Fossils of these carnivores have been found in rocks across Africa, South America, India and Europe dating from the Late Cretaceous, just before the dinosaurs were wiped out 66 million years ago.

Argentina is well known for its abelisaur fossils, with 35 species already described in the country. But almost all of these come from Patagoniain the south of the country, and relatively few dinosaurs have been found in the northwest.

Describing this new species from part of a skull provides vital new knowledge for scientists studying this time in history.

Guemesia ochoai discovered in northern Argentina

Guemesia ochoai, whose puzzle was enclosed in this block, was discovered in northern Argentina, where abelisaurs are rarely found. Credit: © Anjali Goswami

Abelisaurid ancestor?

The puzzle, including the upper and back parts of the skull, was found in the Los Blanquitos formation near Amblayo in northern Argentina in rocks dating back 75 to 65 million years. This means that this animal lived just before the mass extinction at the end of the Cretaceous which saw the extinction of most dinosaurs.

A unique feature of this dinosaur are rows of small holes in the front of its skull called foramina. The researchers suggested that these holes could have allowed the animal to cool down, as blood was pumped through the thin skin at the front of the head to release heat.

Like many abelisaurids, the skull has a “remarkably small” braincase, but even then the new species has a skull about 70% smaller than any of its relatives. This reduced size may indicate that it is a juvenile, but there is conflicting evidence on this.

A similar lack of clarity extends to its other features, including thin parts of the skull and, unlike other abelisaurids, a lack of horns. It has been suggested that this could mean that the new species is near the bottom of the abelisaur family tree or closely related to the ancestors of the rest of the group.

Although some details are still unclear, there are enough unique features of the dinosaur to convince researchers that it is a new genus and species, which they named Guemesia ochoai. It is named after General Martin Miguel de Güemes, a hero of the Argentine War of Independence, and Javier Ochoa, a museum technician who discovered the specimen.

While many questions still surround the newly described abelisaurid, this adds to a growing body of evidence suggesting that northwestern Argentina had a unique set of creatures different from those found elsewhere in the world at that time. .

These include podocnemidoid turtles like Stupendemys geographicusa die largest aquatic reptile have ever lived.

Scientists now hope to discover more specimens of Guemesia ochoai and his relatives to learn more about life in ancient Argentina. They particularly focus on the period just before and after the mass extinction at the end of the Cretaceous to understand how this massive event shaped life on Earth.

In addition to Guemesia ochoaithe team has already discovered several other interesting species, from fish to mammals, which they are currently describing.

Anjali explains that there is still a lot to learn from fossils in northern Argentina.

“Understanding huge global events like a mass extinction requires global datasets, but there are many parts of the world that have not been studied in detail, and tons of fossils remain to be discovered,” she says. .

“We left some exciting fossils in the ground on our last trip, not knowing that it would be years before we could return to our field sites. Now, we hope it won’t be long before we can finish digging them up and discover many more species of this unique fauna.

Reference: “First definitive abelisaurid theropod from the Upper Cretaceous of northwestern Argentina” by Federico L. Agnolín, Mauricio A. Cerroni, Agustín Scanferla, Anjali Goswami, Ariana Paulina-Carabajal, Thomas Halliday, Andrew R. Cuff and Santiago Reuil, February 10, 2022, Journal of Vertebrate Paleontology.
DOI: 10.1080/02724634.2021.2002348

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