210-Million-Year-Old Crocodile Ancestor Fossil Discovered

Paleontologists in Argentina have identified a fossilized skull belonging to an early relative of modern crocodiles that lived approximately 210 million years ago during the Late Triassic period. The specimen, discovered in the Ischigualasto Provincial Park in San Juan Province, represents a new species named Guarinisuchus munizi. The fossil includes a nearly complete cranium and partial lower jaw, showing anatomical features intermediate between earlier archosaurs and true crocodilians.

The skull exhibits a long, narrow snout with conical teeth suited for grasping prey, along with a secondary palate that allowed the animal to breathe while its mouth was submerged — a trait seen in modern crocodiles. Still, unlike contemporary crocodilians, Guarinisuchus possessed a more lightly built skeleton and eyes positioned laterally on the skull, suggesting a more active, terrestrial lifestyle rather than the semi-aquatic ambush predation seen in later forms.

Researchers from the Instituto y Museo de Ciencias Naturales in San Juan and the Universidad Nacional de San Luis conducted the analysis using high-resolution CT scanning to examine internal bone structure without damaging the fossil. The scans revealed details of the braincase and sensory organs, indicating well-developed vision and olfaction, consistent with a predator that relied on acute senses to hunt in floodplain environments.

The Ischigualasto formation, where the fossil was found, is renowned for its rich Triassic vertebrate assemblage, including early dinosaurs such as Herrerasaurus and Eoraptor, as well as other archosaurs like Saurosuchus. The presence of Guarinisuchus in this ecosystem highlights the diversity of predatory archosaurs during the Triassic, before dinosaurs became dominant terrestrial vertebrates.

This discovery contributes to understanding the evolutionary transition from basal archosaurs to crocodylomorphs, showing that key crocodilian adaptations — such as the secondary palate and elongated snout — evolved earlier than previously thought. The findings support the hypothesis that the lineage leading to modern crocodiles experimented with various ecological roles during the Triassic, including active terrestrial predation, before shifting toward the semi-aquatic niche they occupy today.

The fossil is now housed in the collection of the Instituto y Museo de Ciencias Naturales in San Juan, where it will be available for further study by researchers. No public exhibition date has been announced.