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.

Two new fossil mammal localities from the Paleogene of central-western Patagonia are preliminarily described as the basis for a new possible biochronological unit for the early Eocene of Patagonia, correlated as being between two conventional SALMAs, the Riochican (older) and the Vacan subage of the Casamayoran SALMA. The mammal-bearing strata belong to the Middle Chubut River Volcanic-Pyroclastic Complex (northwestern Chubut Province, Argentina), of

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The hairy long-nosed armadillo, currently referred as Dasypus (Cryptophractus) pilosus, is an enigmatic species endemic to montane cloud forests and subparamo of Peruvian Andes. Its strikingly different external features, which include the carapace concealed by abundant hair, the presence of more movable bands, and a slender skull, have raised questions regarding its taxonomic status as subgenus or as genus. This paper assesses this issue based on a cladistic study and provides a detailed comparative description of the species, including the first account on the distinctive ornamentation of its osteoderms. Based on several unique characters in the carapace, skull, mandible, and teeth, as well as on the external phylogenetic position relative to other Dasypus, we favor the assignment of the hairy long-nosed armadillo to other genus. As result, we revalidate the original generic epithet, so that the valid name of the species is Cryptophractus pilosus Fitzinger, 1856.

Late eruption of the permanent dentition was recently proposed as a shared anatomical feature of endemic African mammals (Afrotheria), with anecdotal reports indicating that it is also present in dasypodids (armadillos). In order to clarify this question, and address the possiblity that late eruption is shared by afrotherians and dasypodids, we quantified the eruption of permanent teeth in Dasypus, focusing on growth series of D. hybridus and D. novemcinctus. This genus is the only known xenarthran that retains two functional generations of teeth. Its adult dentition typically consists of eight upper and eight lower ever-growing (or euhypsodont) molariforms, with no premaxillary teeth. All but the posterior-most tooth are replaced, consistent with the identification of a single molar locus in each series. Comparison of dental replacement and skull metrics reveals that most specimens reach adult size with none or few erupted permanent teeth. This pattern of growth occurring prior to the full eruption of the dentition is similar to that observed in most afrotherians. The condition observed in Dasypus and many afrotherians differs from that of most other mammals, in which the permanent dentition erupts during (not after) growth, and is complete at or near the attainment of sexual maturity and adult body size. The suture closure sequence of basicranial and postcranial epiphyses does not correlate well with dental eruption. The basal phylogenetic position of the taxon within dasypodids suggests that diphyodonty and late dental replacement represent the condition of early xenarthrans. Additionally, the inferred reduction in the number of molars to a single locus and the multiplication of premolars represent rare features for any living mammal, but may represent apomorphic characters for Dasypus.

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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