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140 million years ago, to defend itself against predators, a hitherto unknown species of herbivorous dinosaur developed a curious trait: the Bajadasaurus pronuspinax wore some long fine spines that grew from its back and neck.
Nobody has any idea what those battles and struggles for survival were like, but what scientists do know found in the north of Argentine Patagonia the remains of this specimen, of about 9 meters long, is that the animal was the most colorful.
“This species was not notable for its size but for other particular anatomical characteristics: spines inclined forward that ran through the neck and back as a continuation of its vertebrae. They were covered with sheaths that held long horns with a defensive function ”, he told SINC Argentine paleontologist Pablo Gallina, researcher at CONICET and the Azara-Universidad Maimónides Foundation.
Since 2010, this team of researchers has been working in an area known as Bajada Colorada, in the southeastern province of Neuquén, where some colleagues had found small remains of splinters of vertebrate bones and recommended that they go take a look at them.
The first campaign was exploratory: "We went with sunscreen, a cap, black glasses, a canteen and we just started walking," says this scientist. That first year we took things that at that time we didn't even know what they were and we sent them to the laboratory of the Ernesto Bachmann Municipal Museum, in Villa El Chocón ”.
In mid-2013, Gallina returned to this Neuquén town to study the materials. And there, in the laboratory, with the bones already clean, he realized that it was an unknown species: it was the remains of a brontosaurus whom he baptized Leikupal laticauda.
Over time, the researchers realized that that area of reddish rocks, located between the towns of Picún Leufú and Piedra del Águila, hid many more treasures.
Paleontologists found carnivorous dinosaur teeth and skeleton parts of an unknown sauropod that they identified when they saw a large part of the skull and the first vertebrae of the neck, from which a striking spine of 60 centimeters long stood out.
When these fossils were prepared and cleaned in the laboratory, scientists were able to determine that it was a new species. This time, they called it Bajadasaurus pronuspinax: Bajada, in relation to the discovery locality, Bajada Colorada; saurus, which means 'lizard'; pronus, 'leaning forward'; and spinax for 'thorn' in Greek. In other words, ‘Bajada Colorada lizard with spines leaning forward’.
After years of meticulous study, the scientific work is finally published today in the scientific journal Scientific Reports, open access.
Due to the few elements found, paleontologists cannot estimate how much this specimen would have weighed. They do know that his neck would have measured 2.5 meters and that it was an adult specimen, since several of the cranial bones are well fused, something that is not seen in the fossils of younger sauropods.
While among some species of long-necked herbivorous dinosaurs their main defense mechanism was a combination of large size and rapid growth, others developed creative strategies, such as whip tails, armored hide, or bone maces at the tip of the tail.
Bajadasaurus, of the group of the dicreosáuridos, exhibited, instead, a series of long spines with which it tried to dissuade the predators. As the paleontologist Sebastián Apesteguía recalls, the first to become known was Dicraeosaurus, found by German explorers in Tanzania at the beginning of the 20th century. But the most representative is Amargasaurus, discovered by José Fernando Bonaparte - the hero of Argentine paleontology - also in Neuquén in the 1980s.
So far they have found other species of this spiny group: Lingwulong shenqui in China; Suuwassea emiliae in Montana, United States; Brachytrachelopan mesai in the center of Patagonia and, a little further north of this region, Amargatitanis macni Y Pilmatueia faundezi found in 2018 by the Argentine paleontologist Rodolfo Coria.
Throughout the years, its striking thorns aroused the most varied conjectures. Certain paleontologists proposed that they regulated their body temperature.
Others assured that the thorns formed a display crest that improved their communication or made them sexually attractive. It was also proposed that they might have had a fleshy hump between the spines, which allowed them to store energy reserves.
But Argentine scientists are more inclined towards the defense mechanism hypothesis. "We think that if they had only been bare bone structures or with some skin covering, they would have suffered breakages or fractures easily with a blow or when attacked by predators," warns Gallina, first author of the research. For this reason, in this new work we suggest that they would have needed the protection of a keratin corneal sheath as happens in the horns of many mammals, which would give resistance and strength to these delicate spines in the face of any unforeseen event ”.
More dinosaurs, more questions
140 million years ago, Argentine Patagonia was very different than it is today. The Andes mountain range did not yet exist. And the rivers went the other way around: they ran with full force from the east to empty into the Pacific, to the west.
The Bajada Colorada area it was dominated by meadows with little humidity. It was an open environment in a wide river valley, quite warm and comparable to today's African savannas, but with other vegetation: ferns, horsetails, bush-shaped conifers, and some species of the first flowering plants.
"We suppose that this place was at that time an elbow of a river where the remains of various animals were deposited," says the researcher.
From studying the 30 cm long teeth and jaw, paleontologists conclude that these animals would have spent a good part of their lives uprooting small plants: "Thanks to the shape of their eye sockets, close to the roof of the skull, these animals had the ability to observe their surroundings while feeding at ground level."
Bajadasaurus it now joins the about 250 species of dinosaurs found so far in Argentina. While remains have been found from north to south, Neuquén province is a true fossil paradise. It was there that in 1882 the first dinosaur bones were found in South America.
“Around 35 species of dinosaurs have been described in the province of Neuquén, to which must be added the forms known only from fossil footprints and the specimens on which new species have not been erected because they are very incomplete - warns paleontologist Juan Ignacio Canale from the 'Ernesto Bachmann' Municipal Museum, Villa El Chocón–. In recent years the knowledge of new dinosaurs and other vertebrates has multiplied due to the fact that there are more and more scientific groups working ”.
More than answers, the new dinosaur encourages new questions. "The function of these neural spines will continue to be a controversial issue," says Pablo Gallina. Our proposal for the corneal sleeve is one more, although we think it is the most viable. We do not know why there are differences in the orientation and length of these spines within the same group or what their eating habits and other aspects of their paleobiology were ”.
«A new long-spined dinosaur from Patagonia sheds light on sauropod defense system«. Scientific Reports.
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