Chasicotatus peiranoi Esteban & Nasif, 1996

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 : 6-7

Chasicotatus peiranoi Esteban & Nasif, 1996

( Fig. 3 G-L; Table 1)

Chasicotatus peiranoi Esteban & Nasif, 1996: 330 .

MATERIAL REFERRED. — CRILAR-Pv 119, an association of six fixed osteoderms and three complete plus three broken mobile osteoderms.

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 osteoderms. Osteoderms ( Fig. 3 G-I) are sub-rectangular in outline, slightly longer than wide (see Table 1). In lateral view, the thickness progressively increases towards the posterior margin. The dorsal surface of the osteoderms is mostly smooth and foramina are scarce.

The ornamentation pattern of the dorsal surface includes a well-developed central figure and a set of 6-7 peripheral figures. The central figure is rounded in section and elongated. It occupies more than two thirds of the anteroposterior total length of the osteoderms, extending to the posterior margin, where it becomes narrower. It is delimited by a main sulcus in which many small foramina are placed. Though in some osteoderms the central figure deviates slightly towards the lateral margin, in most cases it is straight. Peripheral figures are slightly convex in section, and develop very variable contours, ranging from hexagonal and pentagonal to rectangular. In all osteoderms, there are 2 peripheral figures at either side of the central figure. Instead, anteriorly to the central figure there are 2 to 3 peripheral figures, depending on the osteoderm. All peripheral figures are delimitated by sulci, which are shallower than the main sulcus. Along these sulci there are small foramina, though they are more scarce than in the main sulcus. Additionally, large dorsal foramina are placed at the boundary between main and minor sulci.

At the posterior margin, there is a double row of piliferous foramina. The lower row includes the largest foramina, varying from 4 to 7 in number. These foramina have a great anteroposterior development and are dorsally oriented. In turn, the upper row includes much smaller foramina intercalated between the large foramina of the first row, placed in the upper half of the septum that separates them. There are no foramina at the anterior and lateral margins.

Mobile osteoderms. Osteoderms ( Fig. 3 J-L) are rectangular in outline, much longer than wider (see Table 1). The articular portion represents approximately one third of the total length, and is separated from the ornamented portion by a great transitional area with a flat and unornamented surface. In turn, the ornamented portion includes a central figure and a set of peripheral figures.

The central figure is rounded in section and elongated. It extends straightly from the transitional area to the posterior margin of the osteoderms, extending the entire length of the ornamented portion, while maintaining an approximately constant width. At either side of the central figure there are 3-4 peripheral figures. All figures are delimited by sulci. The main sulcus, which delimits the central figure, is deeper and wider than the sulci that delimit the peripheral figures. As in fixed osteoderms, there are large foramina placed at the boundary between the main and minor sulci.

At the posterior margin, there is a double row of piliferous foramina. The lower and largest row includes 5 to 7 foramina, less dorsally oriented than those of fixed osteoderms. In turn, the upper row is composed by much smaller intercalated foramina, which are more scarce than in fixed osteoderms. Some osteoderms also develop small piliferous foramina in the distal area of the lateral margins.

REMARKS

Chasicotatus includes C. ameghinoi , C. powelli Scillato-Yané, Krmpotic & Esteban, 2010 , C. spinozai Scillato-Yané, Krmpotic & Esteban, 2010 and C. peiranoi . The analyzed

Fixed osteoderms Mobile osteoderms

Taxa Length Width Length Width Vetelia ghandii Esteban & Nasif, 1996 (adult) 22.81-26.67 16.66-24.23 – – V. ghandii (juvenile) 14.72 10.55-12.51 – – Chasicotatus peiranoi Esteban & Nasif, 1996 11.36-14.31 9.13-9.41 20.15-27.85 8.71-9.73 Macrochorobates scalabrinii ( Moreno & Mercerat, 1891) 16.38 11.43 41.81 12.57 Prozaedyus sp. 8.87-9.16 6.11-6.85 15.21 6.23 Paleuphractus argentinus ( Moreno & Mercerat, 1891) 10.57-14.28 9.51-10.23 16.36-24.28 7.27-8.96

material is assigned to C. peiranoi as it bears a double row of piliferous foramina at the posterior margin of the osteoderms (see Esteban & Nasif 1996; Scillato-Yané et al. 2010). It differs from C. spinozai as the latter develops much smaller piliferous foramina, while C. powelli develops more conspicuous foramina at the dorsal surface of the osteoderms (see Scillato-Yané et al. 2010). In turn, C. ameghinoi develops just one row of piliferous foramina at the posterior margin of the osteoderms (see Esteban & Nasif 1996; Scillato-Yané et al. 2010).