Osteoderm morphology in recent and fossil euphractine xenarthrans.

KRMPOTIC, C. M.; CIANCIO, M. R.; BARBEITO, C.; MARIO, R. C.; CARLINI, A. A.

ACTA ZOOLOGICA

Published on behalf of The Royal Swedish Academy of Sciences and The Royal Danish Academy of Sciences and Letters

Lugar: Estocolmo; Año: 2009 vol. 90 p. 339 - 351

0001-7272

Osteoderm morphology in recent and fossil euphractine xenarthransC.M. Krmpotic,*M.R. Ciancio,* C. Barbeito, R.C. Mario and A.A. Carlini*Authors 1 and 2 contributed equally.ABSTRACTThe presence of  osteoderms within the integument, forming a caparace, is one of the most distinctive features of armadillos with the external morphology of these elements forming the basis of most systematic schemes. This is especially true for fossil taxa, where these elements are most frequent in the paleontological record. A detailed study of osteoderms from the cephalic shield and different regions of the dorsal armor of Chaetophractus villosus (Euphractinae, Xenarthra) was made and compared to those of the extant genus Dasypus (Dasypodinae, Xenarthra), and the extinct genus †Eutatus. Three distinct histological zones were recognized: outer and inner zones are thin, formed by regular compact bone, the middle zone is thicker, with large cavities that contain mainly adipose tissue, hair follicles, and sweat and sebaceous glands. The internal structure of †Eutatus (also member of Euphractinae) osteoderms is close to that of C. villosus, consistent with the notion that these taxa are phylogenetically close related. In contrast, Dasypus shows marked differences. Dasypus shows hair follicles associated to both gland types (sweat and sebaceous) and connected to foramina on the external surface. Although not observed in adult C. villosus, it has been documented during embryonic development, only to atrophy later in ontogeny. Furthermore, presence of red bone marrow is rare in C. villosus, but widespread in D. novemcinctus osteoderms. These results suggest an early split of both subfamilies and support the hypothesis that the Euphractinae are more derived than the Dasypodinae.