The strange armored dinosaurs that populated South America

About 100 million years ago, Patagonia was home to one of the largest carnivores that has ever existed on Earth: the Giganotosaurus carolinii, between 12 and 13 meters long and almost seven tons, somewhat larger even than the mythical Tyrannosaurus rex, with which it rivals in the last film of the Jurassic World saga. . It was an amateur fossil hunter, Rubén Carolini, who in 1993 discovered the first fossil of this lethal predator; and in the 30 years since, Argentine Patagonia has become a mecca for paleontological research and scientific tourism.

Considered a world dinosaur factory, the region has the most important paleontological collection in South America and has discovered more than 30 new types of dinosaurs from the late Cretaceous period, between 90 and 100 million years ago. In the middle of its desert landscape flourish museums dedicated to these prehistoric reptiles. And in its deposits continue to happen fabulous discoveries, which change the ideas we had about the evolution of dinosaurs on this continent.

The latest of these surprising findings is the new species named Jakapil kaniukura, which means stone-crested shield bearer, in the ancestral languages of northern Argentine Patagonia. This armored dinosaur was no bigger than a domestic dog. He was less than five feet tall and weighed between four and seven kilos. It was herbivorous and had the front legs much shorter than the hind legs, something that indicates that it could run semi-erect; or better, flee at good speed from the fearsome giganotosaurs, with which it coexisted in Patagonia at the same time of the Cretaceous.

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The discovery of this species inaugurates a new genus within the thyreophores, a group of dinosaurs characterized by the armor that covers the dorsal and upper part of their body. The best known of this genus are the stegosaurus, with pentagonal plates on a vertebral column that culminates with thick spines, and the ankylosaurus, covered by a spiny carapace and a club at the tip of its tail.

What was known so far about this large group, which emerged in the Jurassic (between 200 and 145 million years ago) in the supercontinent of Laurasia, was that the vast majority of species lived in that huge land mass (especially in present-day North America, Europe and China) and that evolution led them to be quadrupeds: Only the most primitive ones walked on two legs, like the skullcap. The discovery of jakapil, however, changes that story in three fundamental ways. Bipedal thyreophores continued to exist much later (until the late Cretaceous) and spread to other parts of the planet (in Gondwana, the continents that today lie below the equator), where until now their presence was unknown. This also allows us to reason that this lineage probably suffered an evolutionary reduction of its front legs, as happened to other species, such as tyrannosaurus and giganotosaurus.

This new species lived in the hostility of the ancient Kokorkom desert (located in the current paleontological area of La Buitrera, in the Argentine province of Río Negro), where everything alive was thorny and hard, including the small jakapil. To survive in that environment he developed a tall and robust jaw that allowed him to eat whatever he could find: seeds, succulents and even wood. Adorned with a stone crest, his peculiar jaw could also have served as a weapon of seduction, although this is, for the moment, only a conjecture.

The description of this holotype was published in the scientific journal Scientific Reports in 2022, by Argentine researchers Facundo Riguetti and Sebastián Apesteguía, from the Félix de Azara Natural History Foundation, the University of Maimonides and the National Council of Scientific and Technical Research (CONICET). The Spanish Xabier Pereda, from the University of the Basque Country, also collaborated.

The remains of the 'Jakapil kaniukura' were found in the paleontological area of La Buitrera, in Argentine Patagonia. AZARA FOUNDATION - CONICET

None of them expected much when they found the first remains in 2013, but everything changed six years later. "They were kept for a while thinking that it could be another animal, because in this area there is an abundance of a particular type of land crocodile, so at first it was thought that it could be that. As there were so many remains, they were not finished cleaning until 2019. Then we began to see that the material was not a crocodile, but had striking, rare characteristics, which we did not know in any other animal of that time in South America. As it was cleaned, our eyes were getting more and more open," recalls Riguetti from the province of Río Negro in a video call shared with Apesteguía, from Buenos Aires, and Pereda, from the Basque Country.

For the Spanish researcher this discovery has been equally astonishing. Especially because of the age of the fossil. "It corresponds to a lineage that was thought to be relict [a remnant of a regressing ecosystem]. It would have been more logical to find it in Jurassic terrain. That it appears in the Cretaceous is a real surprise. Probably in South America and Argentina they will continue to appear. I think that, in terms of thyreophores, there may be more surprises, "predicts Xabier Pereda.

The Kokorkom, which means desert of bones in the Tehuelche language, was an extension of dunes of about a thousand square kilometers, almost like the surface of the current city of a Rome. On that golden field vanished most of the bones of the world's largest dinaosaurs (such as those of giganotosaurus and futalognkosaurus), but underneath were hidden the smallest fossils that Apesteguía dusts off with fascination for 25 years. He explains that the site that today is called La Buitrera "has the particularity of having preserved the small skeletons very well. Every animal the size of a lizard, a mouse, a small dinosaur, that died there in the desert was covered by sand, avoiding the possibility of being eaten by any scavenger carnivore."

The South American Gobi

The site is one of the jewels of paleontology because the quality of preservation of its fossils is exceptional. "That's what's so nice about it, because big dinosaurs are everywhere; But the little animals that lived in the shadow of the giants are much harder to find. It is a bit what happens in some other places in the world such as the Gobi desert (in China), and that is why we usually call La Buitrera The South American Gobi, "says the second author of the research article.

In that sky reptiles flew stalking small creatures that desperately sought shelter. The numerous traces of caves are the current evidence of how they tried to hide from the threats, which came not only from the air but also from land, where gigantic carnivorous dinosaurs, snakes with legs, terrestrial crocodiles, sphenodonts and carnivorous theropods of less than half a meter lived. Apesteguía vindicates that cunning. "The desert is for specialists. Not just any animal could live there. Probably, the large dinosaurs passed through the desert without being affected too much because they had enough reserves of water and food to cross it without blinking."

But the little ones had to manage differently. And hiding wasn't always an option for jakapil, so bipedalism gave him a chance to pick up his pace. The researcher relates it as if he were seeing it. "This little animal is living in an arid, open environment, where it cannot hide and predators are infinitely larger. The defense mechanism can be neither hidden nor stay to confront them. Quick dinos, like this one, can eat in an open environment, be aware of the environment and run away as soon as they see a predator approaching. It's a logical answer for that time and place."

A scientific team worked days in the extraction of the fossil, in the paleontological area La Buitrera.FUNDACIÓN AZARA - CONICET

When living conditions are harsh, the risk of dying is high. Being fast and thorny helps, but it doesn't come. For the species to last, you have to have a large family. "In the Kokorkom there are many individuals of a few species and that is precisely a characteristic also of today's deserts. We are not going to find too many species there, but many individuals of few species." In La Buitrera there are already 400 or 500 specimens of sphenodonts, about 15 specimens of snakes with legs and some vultures. "So far with the jakapilappeared little (a fairly complete specimen), but we know that there are remains in other places, so we assume that at least three or four more will contribute their skeletons," speculates the paleontologist.

The researchers plan to continue analyzing the teeth, legs and shields in detail, with the aim of better understanding how it lived and whether bone plates were related to temperature regulation, display (in fighting or courtship) or defense.

The mere appearance of this species has already transformed what was known about armored dinosaurs, in terms of their expansion in time and space, and promises revision in other groups of dinosaurs. "A bug that appears where we did not expect it changes a lot of things, changes the context. In South America they were practically unknown or there is very little record, and less of this particular type of thyreophores, until the appearance of the jakapil. So this tells us that more finds could be expected not just from armored dinosaurs. Because if these animals arrived in these latitudes and we did not expect it, it can easily happen with other groups or other lineages that have lived in our territory and that we do not know yet, "explains Rigutti with enthusiasm.

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