Cranial anatomy of the Early Triassic trematosaurine Angusaurus (Temnospondyli: Stereospondyli): 3D endocranial insights and phylogenetic implications

Abstract

Background: Trematosaurines are a widespread group of early tetrapods (Temnospondyli, Stereospondyli) known from all continents except South America and Antarctica. They radiated rapidly during the Early Triassic just after the End Permian mass extinction and are of interest to understand the recovery of the ecosystems just after extinction. Trematosaurines disappeared during the Late Triassic. Objective: Herein, a re-description of the genus Angusaurus is presented based on a new specimen. This genus is known from the Early Olenekian (Early Triassic) of Russia and comprises four valid species, although the diagnostic characters that deine some of them are vague and controversial. Methods: The new specimen described, using MicroCT scanner and 3D digital modeling, sheds light on the anatomical details of the external and inner cranial structure, and provides new details of the neurocranium as well as the ontogeny of this genus. Results and Discussion: A cladistic analysis of trematosaurines (including most trematosauroids) confirms the problematic nature of some Angusaurus species and provides a basis for detailed discussion about the phylogeny of trematosaurines.