Osteoderm morphology in recent and fossil euphractine xenarthrans

Abstract

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.

A new cingulate (Mammalia: Xenarthra),Pachyarmatherium brasiliensesp. nov., from the Late Pleistocene of Northeastern Brazil

“…Together with previous work (Hill 2006;Wolf 2007;Krmpotic et al 2008;Wolf et al 2011), our study shows that osteoderm microstructure may hold relevant information regarding the relationships of cingulates, and provide charac-ters diagnostic at the species level. Our results may support the exclusion of Pachyarmatherium from glyptodonts, based on the absence of histological features present in both basal (Propalaehoplophorus) and derived glyptodonts (extensive bone remodeling, fibers arranged in large bundles, and undeveloped layers of compact bone relative to the region of trabecular bone).…”

“…Similarly, the external morphology of the osteoderms of Pachyarmatherium closely resembles that of dasypodine armadillos, such as Dasypus and Propraopus (see Ameghino 1889;Hill 2006;Vickaryous and Hall 2006), although it is also almost identical to that of the basal glyptodont Neoglyptatelus (Carlini et al 1997). Like the armadillos Dasypus (Hill 2006) and Chaetophractus (Krmpotic et al 2008), but unlike glyptodonts and pampatheres, Pachyarmatherium brasiliense is characterized by very thick superficial and deep layers of compact bone (Fig. 3B).…”

“…With the exception of MCC 1089V, which represents a carapace fragment of P. jaguaribensis, they comprise uncatalogued, isolated, eroded osteoderms found in association with catalogued material (other osteoderms and, in some cases, postcrania) held at MCC. We decided to restrict our analysis to Brazilian glyptodontids and Pachyarmatherium because their histological features have not yet been described, while both Dasypodidae and Pampatheriidae were the subject of recent studies (Hill 2006;Krmpotic et al 2008;Wolf et al 2011) The histological sections were deposited at the fossil mammal collection of the Departamento de Geologia (UFRJ) as UFRJ-DG 491-M (Panochthus cf. greslebini), UFRJ-DG 492-M (Pachyarmatherium brasiliense), UFRJ-DG 493-M (Glyptotherium sp.…”

“…Osteoderms show a high degree of morphological and histological diversity (Hill 2006;Wolf 2007), and their external morphology has repeatedly been used in cingulate systematics (Ameghino 1889;Hoffstetter 1958;Paula Couto 1979;Carlini and Scillato-Yané 1996). By contrast, osteoderm microstructure had until recently received relatively little attention (but see Fernandez 1931), although the past five years have been marked by an increased interest in their histology (e.g., Hill 2006;Wolf 2007;Chavez-Aponte et al 2008;Krmpotic et al 2008;Wolf et al 2011), which has provided important insights into cingulate ontogeny and phylogeny (Chinsamy 1997;Krmpotic et al 2008).…”

A new species of Eutatus Gervais (Xenarthra, Dasypodidae) from the Late Pleistocene of the Northern Pampean Region, Argentina

“…From the morphological point of view, the presence of additional foramina near the anterior border (Figure 2.1, af), among the minor figures of fixed osteoderms, and away from the central figure, is a character that had not yet been observed in the genus Eutatus, although this feature is present in another member of the subfamily Euphractinae: Chaetophactus villosus (Krmpotic et al, 2009b;Francia and Ciancio, 2013).…”