Paleuphractus argentinus ( Moreno & Mercerat, 1891 )

Brandoni, Diego, Barasoain, Daniel & González Ruiz, Laureano R., 2023, Late Miocene Dasypodidae Gray, 1821 (Xenarthra, Cingulata) from the Toro Negro Formation (Central Andes, Argentina): diversity and chronological and biogeographical implications, Comptes Rendus Palevol 22 (1), pp. 1-16 : 8-10

Paleuphractus argentinus ( Moreno & Mercerat, 1891)

( Fig. 4; Table 1 )

Dasypus argentinus – Moreno & Mercerat, 1891: 227.

MATERIAL REFERRED. — CRILAR-Pv 122 , several associated elements, including 15 fixed osteoderms, nine mobile osteoderms, one nuchal osteoderm and seven osteoderms of the carapace borders, plus several broken postcranial elements.

GEOGRAPHIC AND STRATIGRAPHIC PROVENANCE. — Quebrada de Las Torrecillas (28°36’37”S, 68°14’14”W), La Rioja Province, Argentina ( Fig. 1). Upper levels of the lower member of the Toro Negro Formation (Messinian-Zanclean; Late Miocene-Early Pliocene).

D ESCRIPTION

Nuchal osteoderm. A single osteoderm ( Fig. 4A) of the nuchal bands was recovered. As in mobile osteoderms (see below), it is divided into an articular and an ornamented portion. However, it is smaller and has a very reduced articular portion in relation to osteoderms of the mobile bands. It has a rectangular outline. The ornamentation includes flat and poorly developed central and lateral figures, which are only partially delimited by shallow sulci. At the posterior margin there is a single row of 6 piliferous foramina but, contrary to the osteoderms of the mobile bands, there are 3 to 4 much larger foramina at the lateral margins.

Fixed osteoderms

These osteoderms ( Fig. 4 B-G) can be either rectangular or pentagonal in outline, and are slightly longer than wide ( Table 1 ). The entire dorsal surface is covered by very small foramina, very abundant in some osteoderms while practically absent in others. All osteoderms have a constant thickness from the anterior to posterior margin.

The ornamentation pattern includes a wide and sub-elliptical central figure surrounded laterally and anteriorly by a variable number of peripheral figures. It extends posteriorly to reach the posterior margin, and deviates slightly toward the external lateral margin of the osteoderm. Towards the posterior margin it widens progressively, occupying more than one third of the osteoderm width. It is delimited by a shallow main sulcus. Anteriorly, this sulcus becomes shallower and disappears, so that the central figure merges with the dorsal surface. In lateral view, the central figure progressively increases its elevation until reaching the posterior margin, where it is much more elevated than the peripheral figures. Peripheral figures vary from 5 to 8, being seven in most cases. These figures are delimited by such shallow sulci and their limits are often diffuse or mostly indistinguishable. Some osteoderms develop large dorsal foramina at all the boundaries between main and minor sulci, while in others they are only present at some boundary or absent.

Two of the fixed osteoderms have a particular morphology, including a deep cavity placed at the anterior limit of the central figure ( Fig. 4F, G). Such cavities are related to the presence of odoriferous glands, which are present in the pelvic shield of many euphractine armadillos ( Scillato-Yané 1982, Redford & Wetzel 1985). This structure has not been previously described for Pal. argentinus .

At the posterior margin, there are several small piliferous foramina, arranged in an irregular row. These foramina are variable in both number (5-10) and size, as some are twice the size of others, and are arranged in a zig-zag row. Although the lateral margins do not bear foramina, the row of piliferous foramina may extend slightly towards the more distal area of the external lateral margin.

Mobile osteoderms

These osteoderms ( Fig. 4 H-K) are rectangular, longer than wide ( Table 1 ). The articular portion represents less than one third of the total length. The transitional area is flat and unornamented. Some osteoderms develop a transverse ridge at the end of the transitional area, delimiting it from the ornamented portion.

The ornamentation pattern is composed by a central figure surrounded by 2 elongated and undivided lateral figures. The central figure is rounded to slightly keeled in section and sub-elliptical, and extends to the posterior margin. In some osteoderms it is straight, while in others it deviates slightly towards the external lateral margin. In contrast to the condition in fixed osteoderms, it gets much narrower towards the posterior margin. The central figure is delimited by a main sulcus, along which there are several dorsal foramina.Towards the anterior area of the ornamented portion, this sulcus becomes progressively shallower, so that the central figure merges with the dorsal surface. Lateral figures are parallel to the central figure. In some cases, some of these peripheral figures are subdivided by shallow sulci.

At the posterior margin there is a single row of 4 to 7 piliferous foramina, much smaller than those of fixed osteoderms. Also, in contrast to those of fixed osteoderms, these foramina are arranged into a straight line. In those osteoderms in which the central figure is slightly deviated, there are 2 to 3 piliferous foramina in the more ventral area of the external lateral margin.

Osteoderms of the marginal rows. These osteoderms ( Fig. 4 L-N) belong to the most lateral rows of the dorsal carapace. They are more elongated than regular osteoderms, and develop an irregular wedge shape. This is a representative morphology of both fossil and extant euphractine armadillos, which usually develop serrated lateral carapace borders (see Scillato-Yané 1982; Krmpotic et al. 2009).

Ornamentation is nearly or entirely absent, although some osteoderms have poorly developed central and peripheral figures. Some osteoderms of the lateral area develop more similar morphologies to those of other carapace areas, having a single row of piliferous foramina at the posterior margin which is absent in those belonging to the carapace border.

REMARKS

Paleuphractus is monotypic, with Pal. argentinus being the only recognized species. The material here analyzed can be assigned to Pal. argentinus based on a low central figure, mobile osteoderms with undivided lateral figures, and small piliferous foramina located on the posterior and external lateral margins (see Scillato-Yané 1982). It differs from Paraeuphractus Scillato-Yané, 1975 in developing dorsal foramina at the intersections between the main sulcus and the minor sulci of fixed osteoderms ( Rodríguez Brizuela & Tauber, 2006), and from Chorobates and Macrochorobates in being smaller, having a less elevated and deviated central figure in both fixed and mobile osteoderms, and developing undivided lateral figures in mobile osteoderms ( Scillato-Yané 1982). It differs from Proeuphractus in having much smaller piliferous foramina at both the posterior and lateral margins ( Perea & Scillato-Yané 1995).