New information on the anatomy and histology of Gracilisuchus stipanicicorum (Archosauria: Pseudosuchia) from the Chañares Formation (early Carnian), Argentina

Abstract

Gracilisuchus stipanicicorum Romer, 1972 is a basal suchian from the Late Triassic Chañares Formation (Argentina), nested in the recently erected Gracilisuchidae, along with Turfanosuchus dabanensis Young, 1973 and Yonghesuchus sangbiensis Wu et al., 2001 from China. The six known specimens of Gracilisuchus Romer, 1972 preserve most of the skeleton, lacking only most of the shoulder girdle and forelimb. Our latest fieldwork has recovered two specimens that preserve previously unknown elements, including the humerus, radius, and ulna, as well as the femur, presacral vertebrae, and paramedian osteoderms. The femur and osteoderms were histologically sectioned, which has never been done for Gracilisuchidae. The anatomical analysis revealed characters in the new elements that improve our understanding of the anatomy of Gracilisuchus. Bone histology revealed that the specimen CRILAR PV 490 died before reaching somatic maturity and that growth was relatively slow compared to other pseudosuchians. This study increases the knowledge of the anatomy of Gracilisuchus and represents a new step towards a broader understanding of Gracilisuchidae and basal suchian clades.

A new early‐diverging probainognathian cynodont and a revision of the occurrence of cf. Aleodon from the Chañares Formation, northwestern Argentina: New clues on the faunistic composition of the latest Middle–?earliest Late Triassic Tarjadia Assemblage Zone

“…The quality and quantity of specimens from this unit reveled an extraordinary faunal association, including “rauisuchians,” proterochampsids, gracilisuchids, dinosauromorphs, pterosauromorphs, dicynodonts, and cynodonts (see summaries in Ezcurra et al, 2017; Mancuso et al, 2014; Marsicano et al, 2015; Rogers et al, 2001). After the original discoveries by the Romer's team, our understanding of the paleontology and geology of the Chañares Formation has been improved as a consequence of several new fossils, taxonomic, phylogenetic, and paleoecological improvements, radiometric datings, and stratigraphic and faunal correlations (Abdala & Giannini, 2000, 2002; Agnolin & Ezcurra, 2019; Agnolin et al, 2022; Bonaparte, 1975, 1997; Desojo & Arcucci, 2009; Escobar et al, 2021, 2023; Ezcurra et al, 2017; Ezcurra, Fiorelli, et al, 2021; Ezcurra, Nesbitt, Bronzati, et al, 2020; Ezcurra, Nesbitt, Fiorelli, et al, 2020; Ezcurra et al, 2019; Ezcurra et al, 2014; Fiorelli et al, 2013, 2018; Gouiric‐Cavalli et al, 2017; Lecuona et al, 2020; Mancuso et al, 2014; Marsicano et al, 2015; Martinelli et al, 2016; Nesbitt & Desojo, 2017; Ponce et al, 2021; Rogers et al, 2001).…”