Homunculus patagonicus Ameghino, 1891

Novo, Nelson M., Tejedor, Marcelo F. & González Ruiz, Laureano R., 2018, Previously unknown fossil platyrrhines (Primates) of Patagonia from the Tournouër collection at the Muséum national d’Histoire naturelle, Paris, Geodiversitas 40 (22), pp. 529-535 : 531

Homunculus patagonicus Ameghino, 1891

NEOTYPE. — MACN-A 5757; partial mandible preserving a complete and worn dentition lacking crowns of the left canine and the incisors. This is a replacement (see Tejedor & Rosenberger 2008) for the lost holotype specimen, MACN-A 634.

GEOGRAPHIC AND STRATIGRAPHIC PROVENANCE. — The neotype MACN-A 5757 comes from Corriguen Aike (= Puesto Estancia La Costa), on the Atlantic coast of Santa Cruz Province between the rivers Coyle and Gallegos, Argentina. Santa Cruz Formation, late-early Miocene (Burdigalian Age), c. 17.5 to 16.7 Ma ( Tauber 1997; Fleagle et al. 2012).

NEW REFERRED MATERIAL. — MNHN.F.SCZ215 (Fig. 2A-C), partial mandible preserving the left ramus with alveoli for left i1-2, c, p2, broken alveoli of p3-4, and complete m1; alveoli for right i1-2, and broken c.

GEOGRAPHIC AND STRATIGRAPHIC PROVENANCE. —MNHN.F.SCZ215 is labeled as “ Homunculus // Coyle 1902-6” (Fig. 2E). Thus, the provenance is certainly nearby the Coyle river on the Atlantic coast of Santa Cruz Province, Argentina. Santa Cruz Formation, late-early Miocene (Burdigalian Age) (see Marshall 1976; Tauber 1997; Buffetaut 2014), approximately 16.1-16.5 Ma ( Fleagle et al. 2012) ( Fig. 1 ).

DESCRIPTION

Based on comparisons, the mandible MNHN.F.SCZ215 is indistinguishable from the cast of the lost MACN-A 634, the type of Homunculus patagonicus . MACN-A 634 is strongly worn but shows several morphological similarities at the alveolar level as well as the crown outline and size of m1. The size and orientation of the alveoli indicate that the specimen had small roots and procumbent, staggered incisors, producing a V-shaped mandible. The small alveolus for the left canine, similar in size to the alveolus of p2, indicates that the canine was small, as seen in the neotype of Homunculus patagonicus (MACN-A 5757) ( Tejedor & Rosenberger 2008).

Compared to MACN-A 635, this specimen has slightly larger alveoli for the canines and a somewhat more robust mandible. Remarkably, the m1 of this new specimen is one of the best preserved lower molars attributed to Homunculus . Its morphology resembles MACN-A 5969b. It has two roots and the trigonid is higher than the talonid, with moderately high and sharp crests. The preprotocristid extends forward closing the trigonid mesially; the paraconid is absent, and there is an oblique cristid connecting the preparacristid. The metaconid is the highest cusp, and is situated relative to the protoconid in a more distal position. The hypoflexid appears relatively deep. It shows a tiny cuspule as seen in the m1 of MACN-A 5969b. The molar has a long cristid obliqua reaching the trigonid wall lingual to the protoconid, while the hypoconid is displaced labially. The entoconid is lower than the hypoconid, with a long entocristid. The talonid basin is relatively wide and deep, showing an incipient and centrally placed hypoconulid (Fig. 2).

Figures

FIG. 1. — MNHN.F.SCZ215, partial mandible of Homunculus patagonicus Ameghino, 1891 with left m1 in lateral left (A), lateral right (B) and dorsal (C) views; D, m2 of MNHN.F.SCZ215; E, MNHN.F.SCZ215 identification label from MNHN.Abbreviations:alv i1, first incisor alveolus;alv i2, second incisor alveolus; alv c, canine alveolus; alv pm2, second premolar alveolus; Man Sym, Mandibular symphysis; Hypd, Hypoconid; Prd, Protoconid; Trid, Trigonid basin; Med, Metaconid; Entd, Entoconido; Tald, Talonid basin. Orientation abbreviations: D, Distal; La, Labial; M, Mesial; Li, Lingual. Scale bar: 1 mm.