Abstract
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.
Highlights
The presence of osteoderms is widely spread among craniates (Sire et al 2009; Vickaryous and Sire 2009), and it is interpreted as a plesiomorphic character of tetrapods
The Euphractinae present more numerous and larger cavities filled with adipose tissue in the osteoderms, as well as more marginal follicles than the Dasypodinae
In the posterior portion of the osteoderm, the marginal follicles are observed in their respective cavities; these follicles may be associated with sweat and sebaceous glands, or only to sebaceous glands, and are always surrounded by loose connective tissue (Fig. 6a)
Summary
The presence of osteoderms is widely spread among craniates (Sire et al 2009; Vickaryous and Sire 2009), and it is interpreted as a plesiomorphic character of tetrapods. The dorsal shield is subdivided into a scapular buckler, a region of movable bands, and a pelvic buckler (e.g., Scillato-Yane 1982; Krmpotic et al 2009; Ciancio et al 2013) (Fig. 1) In addition to this dorsal covering, osteoderms may be scattered within the integument of the rostrum, the ventral part of the trunk, and the dorsum of the limbs, not forming continuous shields in those areas
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