Krmpotic, C.M., Ciancio, M.R., Barbeito, C., Mario, R.C. and Carlini, A.A. (2009). Osteoderm morphology in recent and fossil euphractine xenarthrans. -Acta Zoologica (Stockholm) 90: 339-351The presence of osteoderms within the integument, forming a carapace, 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 palaeontological record. A detailed study of osteoderms from the cephalic shield and different regions of the dorsal armour 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 a member of Euphractinae) osteoderms is close to that of C. villosus, consistent with the notion that these taxa are phylogenetically closely related. In contrast, Dasypus shows marked differences. Dasypus shows hair follicles associated with 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, the presence of red bone marrow is rare in C. villosus, but widespread in Dasypus novemcinctus osteoderms. These results suggest an early split of both subfamilies and support the hypothesis that the Euphractinae are more derived than the Dasypodinae.

The aim of this study was to describe the histological structure of the skin of greater rhea (Rhea americana), a ratite bird native to South America. Skin samples were taken from three regions of the trunk (alar, dorsal and pelvic) in 14 specimens which ages ranged from 7 days to adulthood. Serial sections were obtained and subjected to different staining procedures (haematoxylin and eosin, orcein, Masson's trichrome and Gomori), and a morphometric analysis was carried out on stained slides. In general, both epidermis and dermis showed increased thickness of its layers with age. Some differences between regions can be detected both in epidermis and in dermis; for example in adults and 7‐day‐old birds, the stratum corneum of the alar region was thicker than of the dorsal region. In general, the skin of greater rhea was similar to that described in ratites and other birds (a thin epidermis compared to dermis, dermis with scarce elastic fibres, a slender and vascularized stratum superficiale, collagen fibres arranged in three directions). The scarcity of elastic fibres and the general cross‐weaved arrangement of the collagen fibres in the dermis of the adult greater rhea provide strength and flexibility to the dermis, two important features in leather industry.