Olkasuchus walasto , a new taxon of Aetosauria (Archosauria; Pseudosuchia) from the Los Colorados Formation (Upper Triassic), Argentina

Abstract

The Los Colorados Formation (Upper Triassic, Norian) is characterised by its extensive tetrapod fossil record, especially of archosaurs. As part of this record, Aetosauria (Late Triassic pseudosuchians characterised by the presence of dorsal, ventral and appendicular osteoderms) is represented only by Neoaetosauroides engaeus. In this contribution, we propose a new taxon: Olkasuchus walasto gen. et sp. nov. (PULR-V 246) that consists of an incomplete axial skeleton, partial pectoral and pelvic girdles, partial forelimb and hindlimb, and both articulated and isolated osteoderms. Olkasuchus walasto was incorporated in a phylogenetic dataset based on the latest matrix of Reyes et al. (2024); adding six characters (three from Ezcurra [2016]; three new ones). Olkasuchus walasto was found nested within Desmatosuchinae, being the sister taxon of Neoaetosauroides engaeus. The clade formed by the two species from the Los Colorados Formation is supported by features associated with the anatomy of the ilium. Olkasuchus walasto is diagnosed by two autapomorphies: presence of a ’lateral boss’ on the lateral surface of the postacetabular process and the presence of a posteromedial fold in the greater trochanter. Olkasuchus walasto is the second aetosaur from the Late Triassic Los Colorados Formation.