Interatherium dentatum 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 : 202

Interatherium dentatum Ameghino, 1894a

Holotype. MACN-A 9863 ( Fig. 1 E ), anterior cranial fragment and an almost complete mandible in anatomical connection.

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

Original description ( Ameghino 1894a: 18). “ Par la taille se rapproche de 1’ I. supernum ; il s'en distingue pour posséder une prémolaire de plus à la mâchoire supérieure, c'est-à-dire cinq au lieu de quatre. Les deux premières prémolaires sont coniques, la première ou antérieure étant séparée de la deuxième. La série dentaire supérieure complète occupe un espace de 41 mm ”.

English translation. It is close to I. supernum by its size; it differs from it in having an additional premolar in the maxilla, which means five instead of four. The first two premolars are conical, the first (or anterior) being separated from the second. The complete upper dental series occupies a space of 41 mm.

Comments. Ameghino (1894a) did not add any illustration to the original description. No specimen is indicated as the type material of I. dentatum in Ameghino’s catalogue, and Mones (1986) wrote “MACN?”, which means doubts or lack of information regarding the type that could be housed at the MACN.

There are three specimens assigned to I. dentatum within the Ameghino Collection: the articulated skull and mandible MACN-A 9863, and two fragmented maxillae, MACN-A 9864 and MACN-A 9865, corresponding to two different individuals. These maxillae lack its anterior portion, so the region that should contain the extra premolar is not preserved in any of them; as the areas of breakage are not recent, both specimens are discarded as the type. Instead, MACN-A 9863 matches the original description ( Ameghino 1894a) as it presents an extra alveolus between C and dP1, which is separated from the latter by a distinct diastema. The length of left I1 –M3 series (41.3 mm) also matches the only measurement provided by Ameghino (1894a). Consequently, MACN-A 9863 is considered the holotype of I. dentatum .

Figures

FIGURE 1. Interatherium rodens, holotype MLP 12-2826, right maxilla with alveolus of dP1 and complete dP2 and P3–M3, in occlusal view (A); reproduction of figure 26 (B) from Ameghino (1889, plate 15). Interatherium anguliferum, holotype MACN-A 3444, right maxilla with C and P2–M1, in occlusal view (C). Interatherium interruptum, holotype MACN-A 3445, left maxilla with the alveolus of dP1 and complete dP2–3 and P4–M3, in occlusal view (D). Interatherium dentatum, holotype MACN-A 9863, skull and mandible articulated, left lateral view (E). Scale bar = 10 mm.