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.

Among extant mammals, the presence of osteoderms is limited to armadillos (Xenarthra, Dasypodidae), being one of its distinctive features. The osteoderms are articulated to form a carapace that covers their body dorsally. In this paper we study the integumentary structures of the armadillos Chaetophractus vellerosus, Chaetophractus villosus, Euphractus sexcinctus, and Zaedyus pichiy (Euphractinae), Dasypus hybridus, and Dasypus novemcinctus (Dasypodinae) within a comparative framework, aiming to identify patterns common to the family and to the subfamilies Dasypodinae and Euphractinae, as well as peculiarities of each species. Differences between the two subfamilies were observed in the dorsal integument, related to the production of blood cells and the mobility of the carapace. The Euphractinae present more numerous and larger cavities filled with adipose tissue in the osteoderms, as well as more marginal follicles than the Dasypodinae. These provide thermal insulation that could be related to their distribution in cooler climates. The sebaceous glands associated with surface follicles are also more developed in the Euphractinae and could be related to preventing the desiccation of the cornified scales in arid climates.

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a b s t r a c tThe integument of extant armadillos (Xenarthra, Cingulata) is a unique organ in which complex glandular systems are associated with pilose follicles, dermal ossifications, and cornified scales. Up to date, papers have focused on neither comparative morphology of the skin (dorsal and ventral) nor chronology of the development of interspecific homolog structures. In order to clarify the way in which events occur during development of the integument structures, maturity of other tissues (e.g. skeletal tissues) should be considered. Therefore, we will be able to identify events that have been pre-or post-displaced during ontogenetic development. The aim of this paper is to describe in a developmental and comparative framework the integumentary system of neonates of Dasypus hybridus and Chaetophractus vellerosus. In order to understand the morphology of the different integumentary structures serial histological sections were prepared. Staining techniques included H-E, Masson Trichrome, PAS, orcein and reticulin. To study ossification of postcranial elements, the specimens were cleared and double-stained with alcian blue and alizarin red. Determinations of ossification centers and their progress were recorded through the early uptake of alizarin. The dorsal dermis of neonates from D. hybridus is clearly differentiated into a superficial and deep layer, as in fetuses of Dasypus novemcinctus. In C. vellerosus, however, these layers could not be identified. This suggests a less connective tissue differentiation in the latter species at this stage. Osteoderms in D. hybridus are well differentiated unlike C. vellerosus where no condensations of osteoprogenitory cells are observed. Conversely, pilose follicles and glandular tissues are less developed in D. hybridus. Regarding postcranial elements, ossification centers are less advanced in C. vellerosus than D. hybridus, this is particularly notorious for the vertebral column, sternal, and pelvic girdle elements. Asynchronies between neonates of both species observed on integumentary and postcranial skeletal tissues could match with specific adaptive strategies related to distribution in different environments, and/or different postnatal care.

A new species of Peltephilidae (Mammalia, Xenarthra, Cingulata) (early Eocene–late Miocene) is described here. Thenew taxon is based on three specimens collected from the margins of Arroyo Chasicó, Buenos Aires Province, (Argenti-na), which correspond to the Arroyo Chasicó Formation (late Miocene, Chasicoan SALMA). The new species is charac-terized by osteoderms with a very rough exposed surface showing high longitudinal and well developed crests (two lateraland one central) with deep and ample valleys among them. The new taxon is the only “relictual” xenarthran cingulate ofthe Santacrucian Age (late early Miocene) to be registered for the last time in the Chasicoan SALMA (late Miocene), and represents the youngest record of the family Peltephilidae.

The most complete and continuous fossil record of armadillos is composed mostly by isolated osteoderms, frequently found in paleontological and archaeological sites that bear continental South American mammals. Their external morphology has been used to define several species. In the last decade, many authors have focused on the internal structure of vertebrate osteoderms using histological and paleohistological studies. These studies allowed identification of useful features in systematic and phylogenetic contexts. In armadillos, osteoderms are constituted by compact bone tissue (primary and secondary osteons, and concentric layers or lamellae) that delimits cavities, which could contain different soft tissues (adipose tissue, hair follicles, bone marrow, and sweat and sebaceous glands). Traditional paleohistological techniques have allowed the recognition of homologous cavities to those found in osteoderms of current species and from comparison deduce which kind of tissue could had occupied them. We have recently utilized 3D reconstructions in osteoderms of extant species of armadillos to analyze the micromorphology, disposition, and the relationship of different cavities and understand them in depth. Here, we present the results of the application of paleohistology and microtomography in osteoderms of representatives of diferent taxa of extinct Dasypodidae (Astegotheriini, Stegotheriini, BUtaetini,^Euphractini, Eutatini), which allowed us to compare homologous structures based on their three-dimensional reconstruction. The results, added to the previous external morphology studies, have allowed us to define morphological patterns (consistent within each linage). The variation of the volume and extension of cavities associated with different tissues could be strongly associated with changes in the climate and environmental conditions of the species distribution areas.

Osteoderms are present in a variety of extinct and extant vertebrates, but among mammals, the presence of osteoderms is essentially restricted to armadillos (Cingulata, Dasypodidae). Osteoderms have been proposed to exhibit a variety of functionalities in Dasypodidae, mainly protection and thermoregulation, and they have been considered as one of the synapomorphies of this group. In this study, we use high‐resolution microcomputed tomography to describe the osteoderm micromorphology of several extant species of Dasypodidae in a comparative context. This study allowed the identification, 3D‐reconstruction and volume quantification of different internal structures of osteoderms as well as their interrelations. This detailed characterization of the internal osteoderm morphology was compared in a phylogenetic context to assess the evolutionary trends of the species involved. This enables the identification of distinctive patterns for the most widely recognized clades, the Dasypodinae and Euphractinae with a morphological homogeneity in the microstructure of their osteoderms, in comparison with Tolypeutinae where it has not been possible to establish a common morphological pattern. The most important features for linage differentiation is the degree of compaction of the osteoderms, the number of cavities and the development of hairs. It is likely that the differential development of the various structures occurred as adaptive response to climate changes.