Icochilus trilineatus Ameghino, 1894a

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 : 211

Icochilus trilineatus Ameghino, 1894a

Syntypes. MACN-A 3633 ( Fig. 5 B ), fragmented left maxilla with M2; and MACN-A 3651 to MACN-A 3657 ( Figs. 5 C–H), isolated cheek teeth .

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

Original description ( Ameghino 1894a: 16). “ Cette espèce est de la même taille que l’ I. extensus , dont elle se distingue facilement aussi bien que des autres espèces, par la forme de ses molaires et prémolaires supérieures. Chacune de ces dents porte sur sa face externe un sillon large et profond qui la divise en deux lobules, et sur chaque lobule il y a un sillon étroit et profond qui le divise en deux colonnettes verticales; on voit ainsi sur la face externe de chaque dent, quatre colonnettes séparées par trois sillons, dont celui du milieu beaucoup plus large et les autres deux très étroits ”.

English translation. This species has the same size as Ic. extensus , from which it is easily distinguished, as well as from the other species, by the morphology of its upper molars and premolars. Each tooth presents a broad and deep groove on its external face, which divides it into two lobules, and on each lobule there is a narrow and deep groove that divides it into two vertical columns; as a result, the external face of each tooth exhibits four columns separated by three grooves, the second being the widest whereas the other two are very narrow.

Comments. Ameghino (1894a) did not illustrate this species. According to Ameghino’s catalogue and Mones (1986), MACN-A 3633, a small maxillary fragment with M2, is the type specimen of the species. The ectoloph of this M2 exhibits three perpendicular grooves, one in the middle and one at each lateral lobe, resulting in an ectoloph with four columns as indicated by Ameghino (1894a). Nonetheless, when describing the species, Ameghino (1894a: 16) alluded to the form of its upper molars and premolars, which implies that he had more than one tooth at hand, and therefore MACN-A 3633 cannot be the only type specimen. In this context, in the Ameghino Collection, the lot MACN-A 3651 to MACN-A 3657 contains six isolated teeth (instead of seven as corresponding inventory numbers), five of which (two M3, and three upper molariforms, probably P4 and/or M1/2) show the characteristics mentioned by Ameghino (1894a); thus, we consider them as part of the type series. As the specimens in the lot lack individual labels, it is not possible to identify which is the missing seventh tooth. Therefore, MACN-A 3633 and MACN-A 3651 to MACN-A 3657 (one currently missing) are considered the syntypes of Ic. trilineatus .

Figures

FIGURE 5. Icochilus lamellosus, holotype MACN-A 3631, incomplete skull, in ventral view (A). Icochilus trilineatus, MACN-A 3633, left M2, in occlusal view (B); MACN-A 3651 to MACN-A 3657 in occlusal view (C–H): left P4 or M1/2 (C), left P4 or M1/2 (D), left M3 (E), right P4 or M1/2 (F), right M3 (G), right m3 (H). Icochilus anomalus, detail of photograph of the holotype MACN-A 3634 from Scott’s catalogue (I). Icochilus truncus, holotype MACN-A 3635, right fragmented mandible with alveoli of i1–dp1 and complete p2–m1, in occlusal (J) and lateral (K) views. Icochilus crassiramis, holotype MACN-A 3636, right mandibular fragment with i2–m3, in occlusal (L) and lateral (M) views. Scale bar = 10 mm.