Icochilus undulatus Ameghino, 1889

Fernández, Mercedes, Fernicola, Juan Carlos & Cerdeño, Esperanza, 2019, On the type materials of the genera Interatherium Ameghino, 1887 and Icochilus Ameghino, 1889 (Interatheriidae, Notoungulata, Mammalia) from early Miocene of the Santa Cruz Province, Argentina, Zootaxa 4543 (2), pp. 195-220 : 206-208

Icochilus undulatus Ameghino, 1889

Holotype. MACN-A 373 ( Fig. 3 L ), an incomplete left maxilla with P3–M3.

Age and provenance of the type material. Santacrucian SALMA, early Miocene , Santa Cruz Province ( Argentina).

Original description ( Ameghino 1889: 473). “ Esta especie era de talla intermediaria entre las dos precedentes [ Icochilus extensus and Icochilus excavatus ], de las que se distingue por los molares y premolares superiores de una conformación bastante distinta, particularmente sobre la cara externa. Los premolares superiores tienen las dos aristas perpendiculares de la parte anterior de la cara externa un poco mas anchas, pero mas bajas, sin levantarse sobre el plano de la cara externa como sucede con las dos especies precedentes, separadas por una ranura poco profunda, y la segunda arista seguida hacia atrás de una ranura idéntica á la precedente, de donde resulta que la cara externa de estos dientes presentan tres elevaciones perpendiculares poco elevadas, separadas por dos surcos poco profundos, que dan á la superficie externa de la muela un aspecto ligeramente ondulado, muy diferente del que caracteriza los mismos dientes del I. extensus y el I. excavatus . Los verdaderos molares difieren todavía mas que los premolares, pues las dos aristas externas anteriores están completamente confundidas en una sola columna convexa bastante ancha; cada muela superior presenta así sobre el lado externo dos columnas ó lóbulos perpendiculares poco salientes que corresponden á los dos lóbulos internos, estando separados por una pequeña depresión perpendicular poco profunda, opuesta al pliegue y profundo surco perpendicular del lado interno. Las últimas muelas superiores, y sobre todo el último verdadero molar, se distingue por una corona muy comprimida. La serie dentaria era casi recta ”.

English translation. Intermediate in size between the two previous species ( Icochilus extensus and Icochilus excavatus ), from which it is distinguished by presenting upper premolars and molars with a quite different conformation, particularly on the external face. Upper premolars have the two antero-external perpendicular edges separated by a shallow groove, which are a little wider, but lower, without rising above the plane of the external face, as it happens in the two preceding species; behind the second edge there is an identical depression to that of the preceding one, leading to the external face of these teeth have three slightly elevated perpendicular elevations, separated by two shallow sulci; as a result, the external surface of the premolars is slightly undulated, what markedly differs from Ic. extensus and Ic. excavatus . True molars differ even more than the premolars as the two antero-external edges are completely confused in a single, very wide and convex column; thus, each upper molar has two perpendicular columns or lobes on the external side, which are not very prominent and correspond to the two internal lobes, being separated from each other by a small and shallow perpendicular depression, opposite to the fold and the deep perpendicular groove of the inner side. The last upper molars, particularly M3, are distinguished by a very compressed crown. The dental series was almost straight.

Comments. Ameghino (1889: 473) founded this species based on a maxillary fragment illustrated in his Atlas ( Ameghino 1889, plate 15: fig. 14). According to Ameghino’s catalogue and Mones (1986), the incomplete maxilla MACN-A 373 is the type specimen of the species. This material matches the original diagnosis and illustration provided by Ameghino (1889, plate 15: fig. 14), herein reproduced ( Fig. 3 M ), and it is confirmed as the holotype of Ic. undulatus .

Figures

FIGURE 3. Icochilus excavatus, syntype MACN-A 9681, right maxilla with alveoli of C and dP1 and complete P2–M3, in occlusal view (A); syntype MACN-A 177, broken symphysis, in labial (B) and lingual (C) views; syntype MACN-A 178, fragmented mandible with c–m1, in labial (D) and occlusal (E) views; syntype MACN-A 179, fragmented right maxilla with two molariforms, in occlusal view (F); reproductions of figures 11 (G), 12 (H), 12a (I), 13 (J) and 13a (K) from Ameghino (1889, plate 15). Icochilus undulatus, holotype MACN-A 373, left maxilla with P3–M3, in occlusal view (L); reproduction of figure 14 (M) from Ameghino (1889, plate 15). Icochilus rotundatus, holotype MACN-A 371, incomplete left maxilla with P3–M3, in occlusal view (N); holotype MACN-A 372, left mandibular fragment with p3–m1, in occlusal view (O); reproductions of figures 15 (P) and 16 (Q) from Ameghino (1889, plate 15). Scale bar = 10 mm.