EXACT AND NATURAL SCIENCES

Scientists reveal the existence of a new dinosaur that lived in Patagonia 70 million years ago

This was determined by a study on bone collections that until now had not been identified with any species.


Digitized reconstruction of Patagopelta. Ankylosaurus of the nodosauridae family, such as Patagopelta, are thought to have lived in wetlands.

Through the analysis of different collections of bones found in the town of Salitral Moreno, located south of the city of General Roca (Province of Río Negro), CONICET scientists led a new study which revealed the existence of a new dinosaur that inhabited Argentine Patagonia at the end of the Cretaceous period, about 70 million years ago.The new species, a small ankylosaurus, was named Patagopelta cristata. The work was published in the Journal of Systematic Paleontology.

“The importance of the study lies in the fact that Patagopelta is the first species of ankylosaurus described for the continental territory of Argentina, which fills the existing gap for this group and adds a new thyreophora to the very few incomplete and indeterminate remains known for our country from this type of ornithischian dinosaurs”, says Facundo Riguetti, first author of the work and CONICET doctoral fellow at the Centro de Estudios Biomédicos, Ambientales y Diagnóstico (CEBBAD, Universidad Maimónides) la Fundación de Historia Natural Félix de Azara.

Although in this case the team that studied the fossil remains found in Salitral Moreno was not responsible for the discovery of the bones, the work allows the experts to finish valuing the findings made by different research groups from the 1980s onwards. The bones do not make it possible to reconstruct a complete animal and they do not come from the same individual. However, they were enough for specialists to understand that they were dealing with a new and unique species.

The ankylosaurs are a group of herbivorous quadrupedal dinosaurs, protected by shells on the head and the entire back and tail of the animal, which have an extensive fossil record for the Cretaceous of the northern hemisphere, but very scarce in the southern hemisphere, where only have found a few species in Australia, Chile, Antarctica and Morocco.

Patagopelta is a nodosaurid, one of the two large families, along with the ankylosaurids, into which ankylosaurs are traditionally divided. Nodosaurids are characterized by having large spines in the neck and shoulder area, as well as by lacking the caudal clubs or clubs present in the ankylosaurid group.

The best-preserved element from Patagopelta is the femur, which is complete and shows all the characteristics typical of nodosaurids, and one of the most important and distinctive remains is a portion of the neck armor, which has spines and crests peculiar to this specimen. This is the reason why it was named Patagopelta cristata, which means Patagonian crested shell.

One of the most abundant elements collected in Salitral Moreno corresponds to the individual pieces that make up the extensive protective armor, called osteoderms -bone shields formed under the skin- similar to the shields that can be seen today in the back of crocodiles and alligators. These elements, arranged in parallel rows along the animal’s back and tail, gave the ankylosaur protection while it lived.

 

A small animal

“For an armored dinosaur, Patagopelta is extremely small. Due to the size of the femur, only 25 centimeters long, we estimate that the animal must have been between two and three meters long, while, in general, ankylosaurs are medium-sized or large animals, with an average length of between four and five meters”, says Sebastián Apesteguía, co-author of the study and CONICET researcher at the Félix de Azara Natural History Foundation.

Nodosaurids are a group of ankylosaurs that evolved in the Northern Hemisphere, but towards the end of the Cretaceous, a continental bridge was established between South America and North America, allowing biological exchange between the hemispheres. While long-necked dinosaurs such as titanosaurs migrated to the north, duck-billed dinosaurs and nodosaurid ankylosaurs entered from the north to the south, as well as lizards and mammals such as weasels or opossums. “That is why in South America we only expect to find animals like Patagopelta in rocks from the late Cretaceous, just before the global extinction of the dinosaurs took place,” says Apesteguía.

The diagnosis of the specialists establish that it is possible that the small size of Patagopelta is linked to some event of dwarfism. “One hypothesis is that it is due to the biological event known as ‘island rule’ or insular dwarfism, due to the scarcity of resources, only the smallest specimens have a chance of surviving on the islands, since they demand less maintenance from the environment. And indeed, at the end of the Cretaceous, northern Patagonia was invaded by an arm of the Atlantic Ocean known as the Kawas Sea, which restricted the passage of many species, several of which adapted to life on the northern islands from Patagonia. This is likely related to dwarfism in ankylosaurs and also in the titanosaurs from Salta of that time,” explains Riguetti.

In fact, a few years ago, the same research team described tracks of dwarf ankylosaurs, possibly affected by similar causes, walking on the bottom of a shallow Cretaceous inlet in Bolivia. In this sense, this new species of dwarf ankylosaur broadens the discussion on body mass and paleobiological aspects of ankylosaurs.