EXACT AND NATURAL SCIENCES

Scientists reconstruct the skeleton of an ancestor of the crocodile that lived in Argentina 225 millions of years ago

Two CONICET women scientists led a detailed study of this species’ bones found in La Rioja. The scientists had also participated in the find of the first specimen in Brazil.


The ornithosuchidae are the ancestors of the current crocodiles and dominated the planet much earlier than the appearance of the dinosaurs. PH: Márcio L. Castro.

Although paleontology linked them with the dinosaurs, experts know now that the group of repitiles called Ornithosuchus –which lived during the Triassic period, 225 mya- were actually the ancestors of the crocodiles. CONICET researchers Belén von Baczko of the Argentine Museum of Natural Sciences “Bernardino Rivadavia” (MACN, CONICET) and Julia Brenda Desojo, of the Faculty of Natural Sciences and Museum of the National University of La Plata (FCNyM, UNLP) headed two important studies that were published in the Journal of Vertebrate Paleontology and Acta Paleontologica Polonica.

The first of them was about the description and reconstruction of 90% of the skeleton of the Riojasuchus tenuisceps interpreted from the bones of four specimens found in the late sixties in Formación Los Colorados, in the province of La Rioja, and that there were only some phalanges and vertebrae missing. “They were terrestrial four legged animal who were scavengers, which means that they did not hunt but fed on remains of corpses. Probably, these animals stood on their back legs to run. They were about two meters long and had a snout with tip ending and carved shape”, von Baczko states.

The researchers agree that it was “really necessary to have a current detailed description such as the one we managed to obtain because the only one that was available was the original presentation of the species that did the well known self-taught paleontologist José Bonaparte in 1972 and since then several reptiles have been discovered. We used those ones to make comparisons and enhance our conclusions.” The study allowed us to re affirm the position of Ornithosuchus among the most ancient ancestors of the current crocodiles.

Apart from Riojasuchus t., there is one second species known in Argentina called Venaticosuchus rusconii, found in Formación de Ischigualasto, also in the province of La Rioja. At an international level, there is only a third one: Ornithosuchus woodwardi, which actually was the first appearance of the Ornithosuchus. The specimen was found at the beginning of the twentieth century in Scotland. “Considering that the only fossil remains were found in two countries so far away from each other, we can infer that the geographical distribution of these reptiles was really wide in Pangea, the only supercontinent that was formed during the Paleozoic and began to separate 250 millions of years ago,” Desojo explains.

New unexpected evidence contributed to complete the gaps inside this already known large distribution and led to the second published study: the discovery of a new specimen of Ornithosuchus different from the previous ones, this time in Brazil, a territory without records of the presence of the reptile. Rodrigo Müller is the researcher of the Universidade Federal de Santa María (UFSM), in Rio Grande do Sul. He is in charge of the find and the one who called the Argentine scientists for their experience in this Triassic fauna. Apart from being well preserved the skeleton was quite complete: there are several bones of the skull and the jaw that help to reproduce the silhouette of its head; numerous vertebrae that belong to the neck, the core, the waist and the tail; and the front legs and one of the back that is almost complete.

The new species was named as Dynamosuchus collisensis, and the analyses of the family relationship allowed the experts to know that it is very close to the Argentine V. rusconii. Besides, both are contemporary with O. woodwardi, the one that was found in Scotland. “It was a great honor and a surprise to have been called to participate in the analyses of the pieces, especially because there were few species of this animal in all the world,” the scientists explain and conclude: “This new piece of information enables the reconstruction of the terrestrial ecosystems of a time in which the ancestors of the crocodiles dominated the Earth and dinosaurs only started to exist.”

By Mercedes Benialgo

References:

Belén von Baczko, Julia B. Desojo & Denis Ponce (2020): Postcranial anatomy and osteoderm histology of  Riojasuchustenuisceps and a phylogenetic update on Ornithosuchidae (Archosauria, Pseudosuchia), Journal of Vertebrate Paleontology. DOI:https://doi.org/10.1080/02724634.2019.1693396

Müller, R.T., Baczko, M.B. von, Desojo, J.B., and Nesbitt, S.J. 2020. The first ornithosuchid from Brazil and its macroevolutionary and phylogenetic implications for Late Triassic faunas in Gondwana. Acta Palaeontologica Polonica. DOI: https://doi.org/10.4202/app.00652.2019

About the study:

Belén von Baczko. Assistant researcher. MACNBR, CONICET.

Julia B. Desojo. Independent reseaercher. FCNyM, UNLP.

Denis Ponce. PhD fellow. IIPG.

Rodrigo T. Müller. UFSM. Brazil.

Sterling J. Nesbitt. Virginia University, USA.