Macrochorobates scalabrinii ( 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 : 7

Macrochorobates scalabrinii ( Moreno & Mercerat, 1891)

( Fig. 3M, N; Table 1 )

Proeuphractus scalabrinii – Moreno & Mercerat, 1891: 226.

MATERIAL REFERRED. — CRILAR-Pv 120 , an association of one fixed osteoderm and one complete, plus one broken mobile osteoderm.

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

Fixed osteoderm. This osteoderm ( Fig. 3M) is sub-rectangular in outline, longer than wide ( Table 1 ). Its entire dorsal surface is covered with small foramina. In lateral view, it maintains a constant width from the anterior to the posterior margin.

The ornamentation pattern of the dorsal surface is composed by a large central figure surrounded both laterally and anteriorly by a set of 7 minor peripheral figures. The central figure is keeled in section and sub-elliptical. It is very extended posteriorly, extending beyond the posterior margin of the osteoderm. The central figure is much more elevated than the peripheral figures, and its height progressively increases towards the posterior margin. The central figure is delimited by a main sulcus in which there are several large dorsal foramina. The peripheral figures have a convex surface and develop very variable irregular contours from slightly oval to pentagonal. Their size is variable, as some figures are double the size of others. At each lateral of the central figure there are 3 peripheral figures, while one is placed anteriorly, between the central figure and the anterior margin of the osteoderm. All peripheral figures are delimited by shallow sulci, in which there are no dorsal foramina as also occurs in the main sulcus.

At the posterior margin, there is a single row of 6 posteriorly oriented piliferous foramina of variable size. Additionally, there are several foramina along the entire length of the lateral margins. Among these, the 2 foramina placed in a posterior position are much larger than the others.

Mobile osteoderm. This osteoderm ( Fig. 3N) is broken posteriorly so that the posterior margin is absent. It is rectangular in outline, much longer than wider ( Table 1 ). The articular portion represents approximately one third of the osteoderm total length. The transitional area is short but develops a roughed surface.

The ornamented portion includes a wide and elongated central figure, keeled in section, which extends straightly from the transitional area to the posterior margin, while maintaining a constant width. At either side, there is an elongated and undivided figure, which extends parallel to the central figure. The central figure is more elevated, and separated from the lateral figures by a wide but shallow sulcus. Along this sulcus there are a few small dorsal foramina which are randomly distributed, some of them cluster together.

Along the entire length of the lateral margins there is a single row of several small foramina, which become larger towards the posterior margin. The posterior margin is not preserved.

REMARKS

Macrochorobates includes M. chapalmalensis ( Ameghino, 1908) and M. scalabrinii . The analyzed materials are assigned to M. scalabrinii for having piliferous foramina at the lateral margins of both fixed and mobile osteoderms, which are absent in M. chapalmalensis (see Contreras et al. 2013), and less convex peripheral figures of fixed osteoderms than M. chapalmalensis (see Scillato-Yané 1982).