Panochthus cf. greslebini Castellanos, 1941

Pereira, Paulo Victor Luiz Gomes Da Costa, Victer, Gustavo Duarte, Porpino, Kleberson De Oliveira & Bergqvist, Lílian Paglarelli, 2014, Osteoderm histology of Late Pleistocene cingulates from the intertropical region of Brazil, Acta Palaeontologica Polonica 59 (3), pp. 543-552 : 546-547

Panochthus cf. greslebini Castellanos, 1941

Fig. 4 .

Material.—Uncatalogued isolated osteoderm (section UFRJ-DG 491-M) forming part of the carapace (MCC collection) from Lagoa do Santo, Currais Novos municipality, Rio Grande do Norte, Late Pleistocene.

Description.—In external view, the osteoderm is pentagonal, with a rugose surface ornamented with about 40 hexagonal figures separated from one another by shallow sulci ( Fig. 4A 1 ). By contrast, the internal surface is smooth, gently concave, and perforated by a vascular foramen near the center, as well as several small pits ( Fig. 4A 2 ).

In cross section, the osteoderm is predominantly composed of trabecular bone enclosed by thin superficial and deep layers of compact bone ( Fig. 4B ). The figures ornamenting the external surface give an irregular appearance to the superficial layer of compact bone. Primary bone is hardly identifiable owing to remodeling caused by osteoclasts, but some primary osteons are present. Near the external surface, there are mineralized collagen fiber bundles predominantly oriented parallel to the osteoderm surface ( Fig.4B 2 ), although some are oriented obliquely. Further towards the center of the osteoderm, the collagen fibers show less organization and the bone exhibits signs of extensive remodeling, such as vascular channels enclosed by concentric bone lamellae, indicating bone resorption and subsequent re-deposition.

Between the superficial layer of compact bone and the central trabecular bone there is an intermediate region which cannot be characterized as either compact or trabecular, and includes primary osteons and some small areas of resorption ( Fig. 4B 1 ). Below the latter, the trabecular bone is thick and shows large cavities, with primary osteons occurring in the trabeculae. Finally, the thin deep layer of compact bone contains narrow collagen fibers running parallel to the osteoderm surface ( Fig. 4B 3 ), as well as a few primary osteons.

Stratigraphic and geographic range.—Late Pleistocene of northeastern Brazil.

Figures

Fig. 4. Uncatalogued isolated osteoderm of the carapace of Panochthus cf. greslebini Castellanos, 1941 from the Late Pleistocene of Lagoa do Santo, Currais Novos municipality, Rio Grade do Norte State, Brazil. A. Osteoderm in external (A1), lateral (A2), and deep (A3) views. B. UFRJ-DG 491-M; internal structure of the osteoderm (B1). Paleohistological sections viewed under a petrographic microscope, superficial compact bone (B2); thin deep layer of compact bone and trabecular bone with some resorption areas (B3). Some possible mineralized fiber bundles also occur. Scale bars: A, 10 mm; B1, 5 mm; B2, B3, 1 mm.

Fig. 1. Simplified cladogram showing the phylogenetic relationships of cingulates, modified from Gaudin and Wible (2006) and Porpino et al. 2009). Note that dasypodids, a group traditionally recognized in the systematics of the xenarthrans, actually represent a paraphyletic assemblage.

Fig. 2. Distribution of the studied species within Brazil. Based on Porpino 2009), Porpino and Bergqvist (2002), and Oliveira et al. (2010).

Fig.3. Uncatalogued isolated osteoderm of the carapace of Pachyarmatherium brasiliense Porpino, Fernicola, and Bergqvist, 2009 from the Late Pleistocene of Lajedo da Escada site, Baraúna municipality, Rio Grande do Norte State, Brazil. A. Osteoderm in external view showing the superficial ornamentation (A 1),lateral (A 2)and internal (A 3)views.B. UFRJ-DG 492-M, internal structure ofthe osteoderm (B 1). Paleohistologicalsections viewed under a petrographic microscope, superficial layer of osteoderm (B 2), note the darker region near the top of the section and the uniform distribution of primary osteons marked by pointers; deep layer of compact bone with dark areas (B 3). Scale bars:A, 10 mm; B 1, 3 mm; B 2, B 3, 1 mm.Abbreviations:da, dark areas (see text for details); po, primary osteon; ra, resorption area; so, secondary osteon.