Icochilus senilis 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 : 209

Icochilus senilis Ameghino, 1894a

Holotype. MACN-A 3596 ( Fig. 4 C ), incomplete skull, MACN-A 3597 ( Fig. 4 D ), complete mandible, and MACN-A 3598 to MACN-A 3630 , postcranial elements, all of them from the same individual.

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

Original description ( Ameghino 1894a: 15). “ Cette espèce est de la taille de l’ I. extensus , mais un peu plus robuste; elle se distingue facilement par la deuxième prémolaire inférieure qui n'est pas bilobée, mais de contour elliptique et par conséquent sans sillon vertical, ni sur la face interne ni sur l'externe. La troisième et quatrième prémolaire inférieure ainsi que les vraies molaires, sont plus larges que dans les autres espèces. La deuxième prémolaire supérieure est aussi de contour elliptique et sans sillon. Il y a un diastème assez long entre la canine inférieure et la première prémolaire. Longueur des sept molaires inférieures, 32 mm ”.

English translation. This species is of the size of Ic. extensus , but it is a little more robust; it is easily distinguished by the second lower premolar that is not bilobated but elliptical and, subsequently, without internal and external vertical grooves. The third and fourth lower premolars, as well as the true molars, are wider than in the other species. The second upper premolar is also elliptical and without groove. There is a rather long diastema between the lower canine and the first premolar. Length of the seven lower molars, 32 mm.

Comments. Ameghino (1894a) did not illustrate any specimen of this species. According to Ameghino’s catalogue and Mones (1986), MACN-A 3596 to MACN-A 3630, an almost complete individual, constitute the type specimen of this species. The mandible MACN-A 3597 and the skull MACN-A 3596 present the respective p2 and P2 elliptical in cross section with very shallow lingual and labial grooves. In addition, the dimensions of MACN-A 3597 (length of the diastema c–dp1 = 2 mm; length of the lower tooth row = 32 mm) match those provided by Ameghino (1894a). Therefore, MACN-A 3596 to MACN-A 3630 are confirmed as the holotype of Ic. senilis .

Figures

FIGURE 4. Icochilus robustus, holotype MACN-A 3454, skull, in dorsal view (A); reproduction of figure 97 (B) from Ameghino (1891). Icochilus senilis, holotype MACN-A 3596, incomplete skull, in ventral view (C); holotype MACN-A 3597, incomplete mandible, in dorsal view (D). Scale bar = 10 mm.