Parastegosimpsonia, Ciancio, Carlini, Campbell, and Scillato-Yane, 2013

Ciancio, Martín R., Herrera, Claudia, Aramayo, Alejandro, Payrola, Patricio & Babot, Judith, 2016, Diversity of cingulate xenarthrans in the middle-late Eocene of Northwestern Argentina, Acta Palaeontologica Polonica 61 (3), pp. 575-590 : 580-581

Parastegosimpsonia cf. P. peruana Ciancio, Carlini, Campbell, and Scillato-Yané, 2013

Fig. 4D–F .

Material.—PVL 6569 and MLP 88-V-10-19A, fixed osteoderms; PVL 6409, movable osteoderm; from Antofagasta de la Sierra, Catamarca Province, Argentina; middle member of the Geste Formation (sensu Alonso 1992); middle–late Eocene.

Description.—Small osteoderms similar in size to the extant Dasypus hybridus . The osteoderms are relatively thick, like Stegosimpsonia and Parastegosimpsonia peruana , but thicker than in other Astegotheriini ( Ciancio et al. 2013a) . The fixed osteoderm is subrectangular. The lateral surfaces are straight and smooth, with few isolated pits. The external surface is smoother than in Parastegosimpsonia peruana and exhibits a principal figure, and two anterior and two anterolateral ones. The principal figure is lageniform and flat (without keel) with a short neck, similar to that observed in Parastegosimpsonia peruana . It is limited from the peripheral figures by an almost imperceptible sulcus housing four large foramina symmetrically arranged on each side of the neck of the principal figure, as in Parastegosimpsonia . The anterolateral figures are less evident; they are bounded by superficial grooves. The lateral margins lack foramina, unlike Stegosimpsonia and Parastegosimpsonia . In PVL 6569 no piliferous foramina are observed, but in MLP 88-V-10- 19A, there are three in the posterior margin. The movable osteoderm has a main lageniform figure with a short neck and a medial keel occupying the whole length of the osteoderm. As the fixed osteoderm, it has four foramina in the anterior portion of the sulcus that defines the main figure, and two foramina on the posterolateral surfaces, similar to those present in fixed osteoderms of Parastegosimpsonia peruana . The peripheral figures are represented by two anterolateral figures. The transition area separating the overlapping portion of the osteoderm from the exposed portion is poorly developed and smooth, but exhibits some striations. The piliferous system is poorly developed; it includes two small foramina on the posterior margin.

Measurements.—Fixed osteoderm (PVL 6569): 9.7 mm long, 6.2 mm wide, and 2.4 mm thick, approximately 20% larger than those Parastegosimpsonia peruana . Movable osteoderm: 10.3 mm long, 5.0 mm wide, and 1.5 mm thick.

Remarks. — Ciancio et al. (2013a) described Parastegosimpsonia peruana , based on a fixed osteoderm from Santa Rosa, Peru. The age of the fossiliferous deposits of the Santa Rosa locality is still controversial, but the cingulates suggest an age between the late Eocene–early Oligocene. We consider the Antofagasta remains as similar to this species but there are some differences in the fixed osteoderm (larger size, absence of a keel on the main figure, absence of foramina on the lateral margin). The scarcity of remains of this species (only one fixed osteoderm constitutes the holotype) difficults to test the morphological variation of the osteoderms, hence we cannot confirm the formal assignation of these osteoderms to the Peruvian Astegotheriini . Additionally, we assign a movable osteoderm to P. peruana , based on the following features: the main figure is lageniform with a short neck and a medial keel occupying the whole length of the osteoderm, and the presence of a pair of large foramina on the lateral margin. New and more complete materials would help us to confirm this preliminary assignation.

Figures

Fig. 4. Dasypodines from the middle member of the Geste Formation, middle–late Eocene, Northwestern Argentina.A. cf. Astegotherium sp., fixed osteoderm, MHAS 067; Quebrada El Paso, near the Pozuelos salt flat, Los Andes Department, Salta Province. B, C.?Prostegotherium sp., movable osteoderms, MHAS 024 (B) and PVL 6567 (C); Antofagasta de la Sierra, Catamarca Province. D−F. Parastegosimpsonia cf. P. peruana, fixed osteoderms, PVL 6569 (D) and MLP 88-V-10-19A (E, broken); movable osteoderm, PVL 6409 (F); Antofagasta de la Sierra, Catamarca Province. G. Dasypodinae indet., movable osteoderm, MLP 88-V-10-19; Antofagasta de la Sierra, Catamarca Province. H−J. Movable osteoderms of Stegosimpsonia (H), Dasypodinae indet. (I) and Anadasypus (J). Photographs (A1−G1), line drawings (A2−G2, H−J). H–J, not to scale.