The osteoderm microstructure in doswelliids and proterochampsids and its implications for palaeobiology of stem archosaurs

CERDA, IGNACIO; DESOJO, JULIA; DESOJO, JULIA; NESBITT, STERLING; NESBITT, STERLING; PONCE, DENIS; PONCE, DENIS; CERDA, IGNACIO

ACTA PALAEONTOLOGICA POLONICA

INST PALEOBIOLOGII PAN

Año: 2017 vol. 62 p. 819 - 831

0567-7920

Osteoderms are common in most archosauriform lineages, including basal forms, such as doswelliids and proterochampsids.In this survey, osteoderms of the doswelliids Doswellia kaltenbachi and Vancleavea campi, and proterochampsidChanaresuchus bonapartei are examined to infer their palaeobiology, such as histogenesis, age estimation at death,development of external sculpturing, and palaeoecology. Doswelliid osteoderms have a trilaminar structure: two corticesof compact bone (external and basal) that enclose an internal core of cancellous bone. In contrast, Chanaresuchusbonapartei osteoderms are composed of entirely compact bone. The external ornamentation of Doswellia kaltenbachi isprimarily formed and maintained by preferential bone growth. Conversely, a complex pattern of resorption and redepositionprocess is inferred in Archeopelta arborensis and Tarjadia ruthae. Vancleavea campi exhibits the highest degreeof variation among doswelliids in its histogenesis (metaplasia), density and arrangement of vascularization and lack ofsculpturing. The relatively high degree of compactness in the osteoderms of all the examined taxa is congruent withan aquatic or semi-aquatic lifestyle. In general, the osteoderm histology of doswelliids more closely resembles that ofphytosaurs and pseudosuchians than that of proterochampsids