Comparative histology and ontogenetic change in the carapace of armadillos (Mammalia: Dasypodidae)

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.

Hiding in a Cool Climatic Niche in the Tropics? An Assessment of the Ecological Biogeography of Hairy Long-Nosed Armadillos (Dasypus pilosus)

“…Krmpotic et al (2015) found less adipose tissue in the osteoderms of Dasypodinae than in those of Euphractinae, which may contribute to the high thermal conductance of Dasypodinae and therefore limited cold tolerance. In contrast, McNab (1980) explained the necessity of high thermal conductance to prevent overheating of armadillos in burrows.…”

Osteoderm microstructure of Riostegotherium yanei, the oldest Xenarthra

“…No growth marks were observed in both specimens in longitudinal or transverse sections, with optic microscopic, but thick and rather loose bundles of Sharpey fibers, crossing each other at various acute angles, were seen in transversal sections (Figure. the combining micro-Ct analysis and histological sections, to study the internal anatomy of buckler osteoderms of the extant armadillos Chaetophractus villosus (Desmarest, 1804) and Dasypus hybridus (Desmarest, 1804) (Krmpotic et al 2015, Ciancio et al 2017, provide the data for the association proposed here between the internal cavities and some of the aforementioned internal structures. however, hill (2006) argued that osteoderms of modern armadillos are physically associated with a variety of soft tissues, and in some cases, two or more different tissue types may cause similar osteological features.…”

“…to observe the internal microstructure and 3D volumetric reconstruction of the osteoderms, we used three different software: Ct vox® (version 2.5.0), Dataviewer® (version 1.4.4), and Avizo® Fire (version 7). the key information provided by the micro-Ct analyses is essentially related to the size, distribution, and orientation of the internal cavities (pilosal, glandular, adiposal, neurovascular, and havers and Volkmann channels), as well as secondary remodeling areas of the osteoderm (Cooper et al 2003, Krmpotic et al 2015. the cavities were gray scale filtering and rendered after segmentation of the osteoderms by density, with CtAn.…”

“…the cavities are larger transversally than dorsoventrally, and slightly displaced to the superficial surface of the osteoderm. In the extant Dasypus, these cavities are filled with both yellow and red marrow (hill 2006), or yellow marrow only, since seasonal variation can suppress the development of red marrow (Krmpotic et al 2015).…”

Proximate causes of variation in dermal armour: insights from armadillo lizards

“…This is further complicated by accumulating bodies of evidence supporting the idea that defensive morphologies are not exclusively the outcome of predatorprey interactions, but instead have a multifunctional nature shaped by functional tradeoffs (Rivera and Stayton 2011, Magwene and Socha 2013, Broeckhoven et al 2017a. For example, body armour might play an important role during thermoregulation (Endo et al 2009, Krmpotic et al 2015, Broeckhoven et al 2017a, Ciancio et al 2017, Clarac et al 2017). In addition, besides being a product of natural selection, intrasexual aggression might contribute significantly to variation in the expression of defensive traits (Broeckhoven et al 2017b, English 2018.…”