Prozaedyus sp.

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

Prozaedyus sp.

( Fig. 3 O-R; Table 1 )

Prozaedyus Ameghino, 1891: 295 .

MATERIAL REFERRED. — CRILAR-Pv 121 , two complete plus one broken fixed osteoderms and one complete plus two 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).

DESCRIPTION

Fixed osteoderms. These osteoderms ( Fig. 3O, P) are sub-rectangular in outline, longer than wide ( Table 1 ). The dorsal surface is smooth and small foramina are scarce to absent. Osteoderms maintain a constant thickness from the anterior to the posterior margin.

The ornamentation pattern includes a narrow and elongated central figure which extends to the posterior margin being rounded in section. It can be straight or slightly deviated toward the external lateral margin, and is a bit more elevated towards its posterior margin. It is laterally and anteriorly surrounded by 7-8 peripheral figures which vary from polygonal to elliptical. These figures have similar sizes, except for the one placed anteriorly to the central figure, which is much smaller than the others. The central figure is delimited by a shallow main sulcus, while even shallower minor sulci delimite peripheral figures. Noticeable dorsal foramina are placed at the boundary between minor sulci and main sulcus.

At the posterior margin there is a single row of four small piliferous foramina. All are similar in size and posteriorly oriented. At the distal area of the external lateral margin there are 2-3 small foramina.

Mobile osteoderms. These osteoderms ( Fig. 3Q, R) are rectangular in outline, much longer than wide (see Table 1 ). The length of the ornamented portion is twice that of the articular portion. The articular portion is more elevated than the ornamented portion, and both are separated by a flat and extremely short transitional area.

The ornamentation pattern includes a straight, elongated, and nearly flat central figure surrounded on each side by 4-5 peripheral figures. Its length extends across the entire ornamented portion, from the transitional area to the posterior margin. Along the surface of the central figure there are several small foramina, always placed next to the lateral boundary of the figure. These foramina are absent in the rest of the dorsal surface of the osteoderm. Peripheral figures are sub-rectangular and have similar sizes, except for those placed closer to the posterior margin, which are the largest. The main sulcus, which delimites the central figure, is deeper than in fixed osteoderms. Contrarily, the minor sulci that delimitate peripheral figures are shallow, as in fixed osteoderms. Several prominent dorsal foramina are observable at the junction between main and minor sulci.

Only one osteoderm preserves its posterior margin, where there is a single row of five posteriorly oriented piliferous foramina, larger than those of fixed osteoderms. At the posterior area of the external lateral margin there are 2 small foramina.

REMARKS

Prozaedyus includes Pr. proximus ( Ameghino, 1887) , Pr. exilis ( Ameghino, 1887) , Pr. impressus Ameghino, 1897 (synonym of Pr. planus, sensu Loomis, 1914 ), Pr.Tenuissimus Ameghino, 1897 , Pr. humilis Ameghino, 1902 , and Pr. scillatoyanei Barasoain, Contreras, Tomassini & Zurita, 2020 . The recovered osteoderms are assigned to Prozaedyus sp. for being smaller than other Euphractinae , having a narrow central figure and a single row of piliferous foramina at the osteoderms posterior margin plus small foramina at the distal half of the external lateral margin (see Croft et al. 2009; Barasoain et al. 2020b). Since main diagnostic characters among Prozaedyus species are given by cranial features (see Barasoain et al. 2020b), the preserved specimens preclude a determination at the species level. Prozaedyus differs from Chasicotatus and other Eutatini armadillos in having much smaller piliferous foramina ( Scillato-Yané 1982; Scillato-Yané et al. 2010). It differs from Proeuphractus Ameghino, 1886 in being smaller and not having large foramina along both lateral margins ( Perea & Scillato-Yané 1995). It differs from Chorobates Reig, 1958 in not having an elevated and keeled central figure ( Carlini & Scillato-Yané 1996).