Almost 100 million years ago, the Kokorkom Desert stretched across the region now occupied by the provinces of Río Negro and Neuquén in Argentina; it was a vast system of mobile dunes in a hot and arid climate, shaped by the wind. This fossil-rich zone, which is part of La Buitrera, discovered and studied over the last 25 years by Dr. Sebastián Apesteguía and his team, has been the site of numerous significant paleontological finds. This landscape was home to a diverse community of animals adapted to extreme conditions: legged snakes, lizards, sphenodonts, omnivorous crocodiles, and herbivorous dinosaurs such as Jakapil, alongside carnivores such as Buitreraptor and Alnashetri. In this environment emerged Antusuchus rionegrinus, a medium-sized terrestrial crocodile, comparable in size to a modern dog.

During the Cretaceous period, the supercontinent of Gondwana was home to an extraordinary variety of terrestrial crocodiles whose habits differed significantly from those of modern-day crocodiles. Equipped with long legs positioned under their bodies, they could raise their abdomens and avoid the heat of the sand. Some were omnivorous, some were adapted to eating tough foods, and some, like Antusuchus, were specialized predators. Their laterally compressed, serrated teeth were designed to capture and tear apart prey.

The most distinctive crocodiles in La Buitrera were the uruguaysuchids, including Araripesuchus buitreraensis and A. manzanensis. These animals roamed the desert, feeding on insects, seeds, roots, and other available resources. The presence of a specialized predator such as Antusuchus indicates a greater ecological complexity than was previously thought, expanding the range of ecological niches occupied by vertebrates in the region.

A team of scientists from CONICET (National Council for Scientific and Technical Research, Argentina’s main public research institution), led by Dr. María Lucila Fernández Dumont (Azara-UMai), Dr. Sebastián Apesteguía (Azara-UMai), Dr. Diego Pol (MACN), Dr. Paula Bona (MLP), Lic. Joaquín Pérez Mayoral (CIG) and Dr. Nahuel Vega (CNEA-CAC) analyzed two specimens found near La Piedra Sola, a fossiliferous site belonging to the La Buitrera Paleontological Area. The first specimen preserved a partial skull associated with an exceptionally well-preserved jaw approximately 17 cm in length. The second skull, although incomplete, preserves several associated vertebrae.

Antusuchus rionegrinus is the oldest known species in the Peirosauridae family, which comprises carnivorous, terrestrial crocodiles that lived in the Upper Cretaceous period in South America and Africa. Its phylogenetic position close to the group’s origin offers an opportunity to explore how these crocodiles emerged and what their earliest members were like before the development of the larger forms characteristic of the end of the Cretaceous period.

References:

Fernández-Dumont, M. L. 2025. Juvenile notosuchian crocodiles from the La Buitrera Paleontological area with comments on qualitative ontogenetic characters. Historical Biology 37:7, pages 1715-1728.

Fernández Dumont, M. L., Pol, D., Bona, P., & Apesteguía, S. (2024). A new species of Araripesuchus with durophagous dentition increases the ecological disparity among
uruguaysuchid crocodyliforms. Journal of Systematic Palaeontology, 22(1), 1–27. https://doi.org/10.1080/14772019.2024.2373987

Fernández Dumont, M. L., P. Bona, D. Pol, and S. Apesteguía. 2020. New anatomical information on Araripesuchus buitreraensis with implications for the systematics of
Uruguaysuchidae (Crocodyliforms, Notosuchia). Cretaceous Research 113:104494. https://doi.org/10.1016/j.cretres.2020.104494