75 million years ago, during the Upper Cretaceous, Patagonia exhibited a radically different landscape from today. Where now an arid plain extends, a vast network of rivers and small lagoons flourished, sheltered among sandy elevations and dunes, hosting a rich diversity of aquatic fauna and tropical-looking flora.
An interdisciplinary collective of experts from CONICET (coming from various institutions) and the Universidad de la República de Uruguay made public the discovery of the remains of a completely unprecedented fauna 75 million years old, located about 30 kilometers southwest of General Roca, in the province of Río Negro.
The expedition that led to the discovery was funded by the National Geographic Society. The results were published in the Revista del Museo Argentino de Ciencias Naturales.
This novel fossil fauna includes a wide variety of living beings linked to freshwater environments: various mollusks, abundant fish, numerous sea turtles, some fragments of crocodiles, as well as of different classes of dinosaurs. Among them, about 7 specimens of a new herbivorous species stand out, which researchers named Chadititan calvoi.
Chadititan calvoi: a tiny herbivorous titan
The Chadititan represented a species of herbivorous dinosaur with a long neck belonging to the group of titanosaur sauropods. Within this group, it was a relatively small species that did not exceed 10 meters in length, while the unearthed young specimens did not reach 3 meters in length.
Chadititan was related to relatively small titanosaurs like Rinconsaurus and Pitekunsaurus, within a small group known as rinconsaurids.
“All of them had a particular appearance: a relatively thick neck that culminated in a broad thorax. Widened hips and relatively slender limbs, and a tail that at its base was strongly curved downward, a very rare condition shared with few dinosaurs,” explains the lead author of the study, Federico Agnolín, CONICET researcher at the Museo Argentino de Ciencias Naturales “Bernardino Rivadavia” (MACNBR, CONICET) and at the Fundación Félix de Azara.
All the rinconsaurids, like Chadititan, inhabited a relatively brief period that spanned approximately 80 to 70 million years ago. They became extinct several million years before the meteorite impact that hit the earth about 65 million years ago.
A few remains found in the same area, including a sharp foot claw, allow the identification of the dominant carnivore of the ecosystem: an abelisaur. This was a carnivorous dinosaur about 6 meters in length with a solid skull armed with sharp and pointed teeth like knives. “Abelisaurs were the most common predators of their time, among which the very famous Carnotaurus stands out,” says Agnolín.
A diverse prehistoric ecosystem: turtles, fish, and more
Among the most notable discoveries are the hundreds of freshwater turtle shell plates found at the site, representing over 90 percent of the recovered remains.
“The turtles we found are very similar to those that are abundant today in the rivers and streams of the northern part of our country, but which nowadays cannot be seen in Patagonia,” says Agnolín. Among the remains, those of a large species known as Yaminuechelys were found, whose shell reached a length of 80 centimeters.
Numerous fish remains belonging to groups not commonly found in the area were also unearthed. Particularly garfish (scientifically known as the Lepisosteidae family) and lungfish of the species Metaceratodus kaopen.
Furthermore, the fossils found have allowed to demonstrate the existence of crocodiles and flying reptiles in this area, although the fragments are so incomplete that it is unknown in detail to which species they belonged.
New prehistoric mollusks
Fossil remains of mollusks, including different types of clams and land snails, are very poorly known in the paleontological record due to their small size and fragile shell. Researchers know very little about their history.
However, in this new fauna, about 6 species of mollusks were recorded. The most outstanding is a new species that still does not have a name, but its closest relative is called Aperostoma inca. It is found only in the cloud forests of northern Argentina, over 2000 kilometers away.
“These discoveries allow us to continue reinforcing the idea that the faunas of the Cretaceous Patagonia were very different from those in the rest of the world at that same time. But over time, the lagoons dried up and the region transformed into the desert we know today,” concludes Agnolín.
Research responsible:
The research team responsible for the publication of this great discovery is also composed of Matías Motta, Jordi Garcia Marsà, Mauro A. Aranciaga-Rolando, Gerardo Álvarez-Herrera, Sebastian Rozadilla, Federico Brissón-Egli, Mauricio A. Cerroni, Karen M. Panzeri, Sergio Bogan, Sergio E. Miquel, Diego Pol, and Fernando E. Novas, from MACNBR; Juliana Sterli, from the Museo Paleontológico Egidio Feruglio (MEF); Silvio Casadio, from Universidad Andres Bello, Chile, Sergio Martínez from Universidad de la República (Uruguay), and Leandro M. Pérez from Museo de La Plata (FCNyM, UNLP).
Cover photo: Gabriel Diaz Yanten
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