Homalostylops sp.

Fernández, Mercedes, Zimicz, Ana N., Bond, Mariano, Chornogubsky, Laura, Arnal, Michelle, Cárdenas, Magalí & Fernicola, Juan C., 2021, New Eocene South American native ungulates from the Quebrada de los Colorados Formation at Los Cardones National Park, Argentina, Acta Palaeontologica Polonica 66 (1), pp. 85-97 : 88-89

Homalostylops sp.

Fig. 1C .

Material.—IBIGEO-P 57b, right m2?, Quebrada Grande, Los Cardones National Park, Casamayoran SALMA, Eocene.

Description.—IBIGEO-P 57b is a low-crowned tooth, more brachydont than in species of Boreastylops , and subrectangular in outline, being more mesio-distally expanded (i.e., longer) than labio-lingually expanded (i.e., wide); the trigonid is simple, high and subrectangular in contour, being wider than long; the protolophid is slightly mesio-labially directed, and its labial wall is straight; the paralophid is conspicuous and directs lingually; a lower mesio-lingual cingulid can be identified, which will eventually merge with the paralophid with wear; the metalophid is simple, well developed, and disto-lingually directed, but much less disto-lingually directed and narrower than in species of Boreastylops , and it is higher than the paralophid; there is no trace of a paraconid or any accessory cuspid in the mesial wall of the metalophid; the cristid obliqua is connected to the labial half of the metalophid, more labially than in species of Boreastylops ; the labial sulcus is both transversally and longitudinally deep; the talonid is well developed, subquadrangular in outline, being longer than wide, and labially convex; it is longer, lower, and slightly narrower than the trigonid; the talonid basin is deep and wide; the lophoid entoconid is transversally expanded and connected to the hypoconid region, and its distal face is located mesial to the hypoconulid; the latter is well separated from the entoconid region by a deep valley; the hypolophid is well developed and lingually curved; and a low disto-lingual cingulid connected to the hypoconulid can be recognized.

Remarks.—Due to the combination of features described above, IBIGEO-P 57b can be discarded as a specimen assignable to Boreastylops , which was, up to this contribution, the only Notostylopidae genus recorded in Northwestern Argentina ( Vucetich 1980). Nevertheless, characteristics such as the presence of a lower crown and a narrower talonid are similar to those observed in Paleogene forms from Patagonia such as Notostylops and Homalostylops . Both of these genera exhibit an important morphological resemblance (see Simpson 1948); as a result, and primarily due to the size of IBIGEO-P 57b (see Table 1 ) that falls within the range of Homalostylops (see Simpson 1948 for comparative measurements of Notostylops and Homalostylops ), we identify the specimen as Homalostylops sp. This undoubtedly represents the first record in Northwestern Argentina of this genus, previously known only from Patagonia.

Figures

Fig. 1. New fossil materials of Litopterna,Astrapotheria, and Notostylopidae from the Quebrada de Los Colorados Formation exposed at Quebrada Grande locality, Los Cardones National Park (Salta Province), Casamayoran SALMA, Eocene. A. cf. Ernestokokenia sp. (IBIGEO-P 65), fragmented left upper cheek tooth in occlusal view.B.Astrapotheria indet.(IBIGEO-P 66), left maxillary fragment with three broken molariforms in lingual (B1) and occlusal (B3) views, and detail showing Hunter-Schreger bands (B4); dashed area in B2 indicates broken or missing dental areas. C. Homalostylops sp. (IBIGEO-P 57b), right m2? in occlusal (C1), lingual (C3), and labial (C4) views. D.?Homalostylops sp. (IBIGEO-P 57a), left m1? in occlusal view. Photographs (A1, B1, B3, B4, C1, C3, C4, D1), explanatory drawings (A2, B2, C2, D2).