Advances on paleobiology of aetosaur Aetosauroides scagliai (Pseudosuchia: Archosauria) based on osteohistological analyses of its appendicular bones

PONCE, DENIS A.; DESOJO, JULIA B.; CERDA, IGNACIO A.

Santiago de Chile

Congreso; I Congreso Latinoamericano de Evolución; 2021

Sociedad Chilena de Evolución, Asociación Colombiana de Biología Evolutiva & Sociedad Argentina de Biología Evolutiva

Aetosaurs were a group of heavily armoured pseudosuchians, recorded in most of the Triassic continental deposits worldwide. Several osteohistological contributions of aetosaurs focused mostly in their osteoderms, but faintly in appendicular bones. Here we performed the first osteohistological study since appendicular bones on a South American aetosaur, Aetosauroides scagliai. The samples include humerus, femur and tibia of two specimens, PVL 2073 (holotype) and PVL 2052. Overall, these exhibit cortical bone mostly formed by highly vascularized fibrolamellar bone present in the inner portion of the cortex, mixed with scarce parallel-fibered bone. Also, show parallel-fibered bone in the outermost portion of the cortex. Evaluating the value as skeletochronological tools of appendicular bones vs. osteoderms, this results variable. The former are useful in first stages, while osteoderms are more reliable in late stages, due the particular growth of osteoderms. Through morphological (neurocentral sutures) and histological (absence of EFS and LAGs distribution) information, is inferred that sexual maturity in PVL 2073 precedes the neurocentral fusion of caudal vertebrae. A general growth pattern that includes a first rapid stage followed by a slowly stage is reported. Nevertheless, the growth rate and the presence of parallel-fibered bone embedded into fibrolamellar bone layers adds more variation within Aetosauria. Using a statistical model that combine microanatomical and morphological data, is inferred a terrestrial lifestyle for Aetosauroides, which fits with previous analyses.