Growth curve of Aetosauroides scagliai Casamiquela 1960 (Pseudosuchia: Aetosauria) inferred from osteoderm histology

Abstract

Recent paleohistological studies on paramedian osteoderms of aetosaurs revealed the presence of growth lines (lines of arrested growth or LAG’s) and a minimal or nonexistent secondary remodelling in the bone matrix of these elements. This feature allows estimating the age of individuals through growth line count. In the present contribution we study the growth curve of the South American aetosaur Aetosauroides scagliai. We estimated the age (obtained from LAG’s counting) and body size (body length and body mass were used as proxies) of different aetosaur specimens in order to reconstruct the growth curve of the South American species. The data obtained for Aetosauroides scagliai was compared with that of other aetosaurs, such as Neoaetosauroides engaeus, Aetosaurus ferratus, Aetobarbakinoides brasiliensis, Typothorax coccinarum, and Paratypothorax sp. Our results indicate that, if body length is considered as proxy, all studied aetosaur specimens have a similar or almost identical growth rate. However, important variations arose among aetosaur taxa if body mass is considered as proxy, which would be related with a body morphology ranging from slender (e.g. Aetobarbakinoides brasiliensis) to very wide (Typothorax coccinarum) morphotypes. In comparison with extant pseudosuchians, (i.e. crocodylians), Aetosauroides scagliai possesses a relatively lower growth rate.