NEW INFORMATION ABOUT THE OSTEODERM HISTOLOGY OF AETOSAUROIDES CASAMIQUELA (ARCHOSAURIA: AETOSAURIA)

IGNACIO A. CERDA; JULIA B. DESOJO

Plaza Huincul

Jornada; Reunion Anual de Comunicaciones de la Asociación PAleontológica Argentina; 2014

One of the most striking features of the aetosaurs, is the possession of an extensive bony armour composed by dorsal, ventral, and appendicular osteoderms. Recent studies, mostly focused on dorsal armour, have provided information about the origin and development of these structures. With the purpose of establish the main histological changes during the ontogeny and the degree of histological variation between osteoderms of different regions within the armour, we analyze the bone histology of dorsal (paramedian and lateral), ventral and appendicular osteoderms of Aetosauroides scagliai Casamiquela. Eight osteoderms from a small (PVL-2073) and a large (PVL-2052) bodied individuals of A. scagliai were analyzed (one paramedial, one lateral, one ventral and one appendicular for each individual). All the osteoderms analyzed are compact structures characterized by: a basal cortex of parallel-fibred bone tissue (PFB); a core fibro-lamellar bone (FLB); and an external cortex of lamellar bone tissue (LB). Also, interwoven structural fibres (ISF) are well formed in the basal cortex of the appendicular osteoderm of PVL PVL-2073. Lines of arrested growth (LAGs) are developed mostly in the basal and marginal areas of each element. The spatial distribution of the LAGs indicates that the osteoderms mostly develop toward the lateral/medial margins and basal surface. Presence of FLB in the internal core indicates high growth rates in the osteoderms. Both FLB and PFB are congruent with an intramembraneous ossification. Nevertheless, the presence of SFB in appendicular osteoderms indicates that metaplastic ossification occurs at least during the last stages of development in some elements.