Eoviscaccia frassinettii, Bertrand & Flynn & Croft & Wyss, 2012

Bertrand, Ornella C., Flynn, John J., Croft, Darin A. & Wyss, Andre R., 2012, Two New Taxa (Caviomorpha, Rodentia) from the Early Oligocene Tinguiririca Fauna (Chile), American Museum Novitates 2012 (3750), pp. 1-36 : 16

Eoviscaccia frassinettii , new species

Figure 5 ; table 3

HOLOTYPE: SGOPV 2935 , partial right mandible bearing p4–m3 and incisor.

REFERRED SPECIMENS: Known only from the holotype.

ETYMOLOGY: Species named in honor of our esteemed colleague and friend, Daniel Frassinetti, who recently passed away. Daniel, a collaborator on our earliest paleontological projects in the Chilean Andes , was responsible for greatly enhancing the MNHN-S fossil vertebrate collections while chief of the paleontology section, and was an unwavering supporter of international scientific collaborations.

DIAGNOSIS (modified from Vucetich, 1989): Eoviscaccia is characterized by bilobed hypsodont cheek teeth, with fossettes/ids persisting relatively late in wear; hypoflexus/id disappearing only after extreme wear; lobes triangular in occlusal outline in young and moderately worn individuals rather than rectangular as in the other pan-chinchillids; roots may incipiently close in older individuals.

We amend the diagnosis of Eoviscaccia with the following observations concerning the lower dentition: in advanced wear the mesial margin of the anterior lobe becomes concave; a narrow isthmus of dentine connects the lobe pairs lingually; and the anterior lobes are thicker mesiodistally than their posterior counterparts. Enamel covers all faces of the cheek teeth but is thin on the anterior faces of both lobes on the molars, on the anterior face of the posterior lobe on the premolar, and on the labial faces of the posterior lobes of all four cheek teeth. Cementum fills the hypoflexid. The hypoflexid hooks posteriorly at its medial terminus, failing to reach the lingual side of the tooth as in most other pan-chinchillids.

Diagnosis of E. frassinettii , n. sp. (figs. 5, 6; table 5): The largest lower cheek tooth in E. frassinettii is m1, whereas in E. boliviana it is m2 ( E. australis is known only from isolated teeth). The hypoconid region is more rectangular labially in E. frassinettii than in E. boliviana and E. australis . The m1–2 protoconid region is oblique in E. frassinettii and E. boliviana (slightly less so in the latter), but transverse in E. australis . The anterior face of p4 is sheathed in enamel in E. frassinettii whereas this region is bare (or the enamel is greatly reduced) in E. australis and E. boliviana . As in E. boliviana and E. australis , enamel occurs on the lingual faces of the anterior lobes of the lower molars in E. frassinettii (although this enamel thins in late wear at least in the former two taxa). Furthermore, in SGOPV 2935, whatever its precise stage of wear, the lophids are oblique rather than transverse (compared to E. boliviana and E. australis ), and the p4 anterofossettid appears to persist later in wear, filling with cement.

Figures

FIG. 5. Holotype of Eoviscaccia frassinettii (SGOPV 2935): (A) photograph and (B) line drawing of right p4–m3 in occlusal view; (C) photograph and (D) line drawing in labial view. Abbreviations: Al, anterior lobe; Atfd, anterofossettid, E, entoconid; H, hypoconid; Hfxd, hypoflexid; M, metaconid; P, protoconid; Pl, posterior lobe.