Researchers in Argentina have discovered a new — and pretty armless — species of dinosaur.
Christened Guemesia ochoai, it was a species of abelisaurid, a clade of dinosaurs that roamed today’s Africa, South America, and India, and lived around 70 million years ago. Based on its age, researchers believe that this species was a close relative of the ancestors of all abelisaurids.
The animal’s partially-complete fossil skull was unearthed in Argentina and points to a unique ecosystem that developed in the area during the Late Cretaceous. The discovery is quite exciting as the area where it was found has yielded very few abelisaurid fossils, so it fills in an important piece of its historical puzzle.
Armless in Argentina
“This new dinosaur is quite unusual for its kind. 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,” says Professor Anjali Goswami, co-author of the study describing the species and a Research Leader at the Natural History Museum of London.
“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.”
By the time this species emerged, the ancient supercontinent of Pangaea had already begun to break apart forming Gondwana and Laurasia. The former would, in turn, split into the major continents in the Southern Hemisphere today and India.
Despite these landmasses slowly drifting apart, species could still move between them, so researchers assume that the fauna of these landmasses remained quite similar, as animals migrated between them. Abelisaurids were among these species.
Abelisaurids were top predators in their ecosystems, preying even on the mighty Titanosaurus. One of their most defining features was the front limbs; even shorter than those of the T. rex, these were virtually useless. In other words, the species did their hunting without being able to grasp, relying instead on their powerful jaws and necks to capture and subdue prey. They seem to have been quite successful at it, too: fossils of these dinosaurs have been found in rocks across Africa, South America, India, and Europe, dated all the way to the extinction of the dinosaurs 66 million years ago.
Although Argentina is well-known for abelisaur fossils (35 species have been discovered here so far), the overwhelming majority of these were discovered in Patagonia, in the country’s south. The north-western stretches of the country have yielded precious few. The newly-discovered skull joins this exclusive list.
The fossil, consisting of the braincase with the upper and back parts of the skull, was unearthed in the Los Blanquitos Formation near Amblayo, in the north of Argentina. The rocks it was encased in have been dated to between 75 and 65 million years ago. In other words, this specimen lived very close to the end-Cretaceous mass extinction, the event that wiped out the dinosaurs.
Like other abelisaurids, the skull contains a “remarkably small” braincase, according to its discoverers; its cranium is around 70% smaller than that of any of its relatives. This could suggest that the animal was a juvenile, but this is yet unconfirmed. One distinguishing feature of the dinosaur is a series of small holes at the front of its skull, arranged in rows, known as foramina. Researchers believe these holes helped the animal cool down, by allowing blood pumped into them (and covered by the thin skin at the front of the head) to release the heat it contained.
In contrast to other species of abelisaurids, the skull completely lacks any horns. This suggests that the species is among the first to emerge in the abelisaurid clade before these dinosaurs evolved horns.
Given that there is enough evidence to distinguish it as a new species, the team christened it after General Martin Miguel de Güemes, a hero of the Argentine War of Independence, and Javier Ochoa, a museum technician who discovered the specimen.
“Understanding huge global events like a mass extinction requires global datasets, but there are lots of parts of the world that have not been studied in detail, and tons of fossils remaining to be discovered,” Professor Anjali says.
“We left some exciting fossils in the ground on our last trip, not knowing that it would be years before we could get back to our field sites. Now we are hoping that it won’t be too much longer before we can finish digging them up and discovering many more species from this unique fauna.”
The paper “First definitive abelisaurid theropod from the Late Cretaceous of Northwestern Argentina” has been published in the Journal of Vertebrate Paleontology.