Dermal armour histology of Aetosauroides Casamiquela, 1960 (Archosauria: Aetosauria) from the Upper Triassic of Argentina and Brazil


One of the most striking features of the aetosaurs is the possession of an extensive bony armour composed by dorsal, ventral, and appendicular osteoderms. In this contribution we present our results of the bone microstructure analysed of these elements in the South American aetosaur Aetosauroides. In general, osteoderms are compact structures characterized by the presence three tissue types: a basal cortex of poorly vascularized parallel-fibred bone tissue; a core of highly vascularized fibro-lamellar bone; and an external cortex of rather avascular lamellar bone tissue. Sharpey fibres are located in the internal core, toward the lateral margins and aligned parallel to the major axis of the plate. No evidence of metaplastic origin was reported in the osteoderms. The bone tissue distribution reveals that the development of the osteoderm begins in a position located medial to the dermal plate midpoint, and the main sites of active osteogenesis occur towards the lateral and medial edges of the osteoderm. The ornamentation in Aetosauroides plates is originated and maintained by a process of resorption and redeposition of the external cortex, which also includes preferential bone deposition in some particular sites. Given that no secondary reconstruction occurs in the osteoderms, growth marks are well preserved and they provide very important information with regard to the relative age and growth pattern in Aetosauroides.

Fuente: XXV Jornadas Argentinas de Paleontología de Vertebrados, San Luis 2010.
Foto: solo a modo ilustrativo.