DESOJO Julia Brenda
congresos y reuniones científicas
OSTEODERM MICROSTRUCTURE OF THE RAUISUCHIAN ARCHOSAURS FROM THE SANTA MARIA FORMATION (MIDDLE-LATE TRIASSIC) OF BRAZIL
CERDA, IGNACIO; DESOJO, J. B.; SCHEYER, TORSTEN; SCHULTZ, C.
Congreso; IV Congreso Latino-Americano de Paleontología de Vertebrados.; 2011
In this contribution we analyse and discuss the microanatomy and histology of postcranial osteoderms of rauisuchians from the Santa Maria Formation (Middle-Late Triassic) of Brazil. The studied sample includes osteoderms of Prestosuchus chiniquensis Huene 1938 (UFRGS-PV0156T and UFRGS-PV0629T) and two undetermined rauisuchians (UFRGSPV0152T and CPEZ-239). Whereas the osteoderms of UFRGS-PV0156T and CPEZ-239 have a rather compact structure, specimens UFRGS-PV0629T and UFRGSPV0152T show a diploe architecture, with a central cancellous core bordered by two compact cortices. Both external and basal cortices are composed of poorly vascularised, coarse parallel-fibred bone and networks of overcrossing mineralized fibre bundles. The internal region of the non-remodelled specimens consists of a highly fibrous bone whose coarse fibres show regionally different orientations. Growth marks are well recorded in both basal and external cortices. Differences in the bone microstructure (compact vs. diploe) appear to be related to the ontogenetic stage of specimens (osteoderms of the older specimens are more remodelled). Hence, age estimation based on the count of growth marks in rauisuchians osteoderms is only reliable in the first stages of the ontogeny. Bone histology reveals that osteoderms mainly originated through direct mineralization (metaplasia) of the dermis, although other mechanisms are probably also involved, as suggested by the presence of fibro-lamellar bone in core areas of other rauisuchian osteoderms (Scheyer and Desojo, in press).