Pachyarmatherium brasiliense Porpino, Fernicola, and Bergqvist, 2009

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 : 545-546

Pachyarmatherium brasiliense Porpino, Fernicola, and Bergqvist, 2009

Fig. 3 .

Material.—Uncatalogued isolated osteoderm (section UFRJ-DG 492-M) forming part of the carapace (MCC collection) from Lajedo da Escada, Baraúna municipality, Rio Grande do Norte, Late Pleistocene.

Description.—The osteoderm is hexagonal in external view. While the external surface, though eroded, bears a main figure surrounded by peripheral figures located in the corners and separated from one another by sulci ( Fig. 3A 1 ), the internal surface of the osteoderm is smooth and shows no perforations ( Fig. 3A 3 ). In cross section, the osteoderm resembles turtle shells (e.g., Zangerl 1969) in being composed of well-developed superficial and deep layers of compact bone (the inner and outer tables) enclosing a central region of trabecular bone, as previously observed by Hill (2006).

The superficial layer of compact bone contributes about 25% of the total thickness of the osteoderm ( Fig. 3B 1 ), conmineralized fiber bundles tains numerous aligned primary osteons ( Fig. 3B 2 ), and itself consist of two distinct zones: (i) a dark superficial layer for which internal details are difficult to observe owing to its color; (ii) a lighter deep layer, including some resorption areas and secondary osteons. No fibre bundles were observed in the superficial layer. The central region of the osteoderm is relatively thin and consists of spongy, trabecular bone showing some resorption areas (“erosion rooms” sensu Main et al. 2005). Although this region has undergone some remodeling by secondary osteons, primary osteons also occur. Like the superficial layer, the deep layer of compact bone also displays a dark zone, but, unlike in the former, the dark areas occur as isolated spots ( Fig. 3B 3 ). As a whole, the deep layer of compact bone is thicker than the superficial one, and contains fiber bundles oriented horizontally and obliquely relative to the surface. There is only one secondary osteon, and primary osteons are completely absent. Marginal fibers are present, but very narrow.

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

Family Panochthidae Castellanos, 1927

Genus Panochthus Castellanos, 1941

Type species: Glyptodon tuberculatus Owen, 1945 ; Pleistocene , Buenos Aires, Argentina .

Figures

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.

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).