Oxyodontherium zeballosi Ameghino, 1883 (Panperissodactyla, Litopterna, Macraucheniidae) from the Neogene of Uruguay

Macraucheniidae comprises middle to large-sized herbivores characterized by an elongated skull, neck, and limbs. Diagnostic features of the family include a mesaxonic foot with three functional digits, a vertebral artery canal passing through the neural arch of most cervical vertebrae, and a third trochanter on the femur. This contribution provides a full comparative description of a macraucheniid mandible from an adult specimen recovered from Neogene strata in Kiyú, San José Department, Uruguay. The specimen exhibits several features consistent with an assignment to Oxyodontherium zeballosi, as follows: the m1 and m2 with fairly acute labial edges of mesial and distal lobes; talonid wider than trigonid, with thin entoconid linked to the hypolophid by an entolophid; hypolophid long and oblique; m3 with shorter trigonid, wide ectoflexid, and no entoconid non entolophid; low mandibular ramus of uniform high from anterior to posterior end. For further comparisons, an analysis of the holotype of Oxyodontherium zeballosi was performed using CT scans. This new specimen is significant because it represents the most complete mandible of the species reported to date, substantially improving our morphological knowledge. Additionally, it constitutes the first reliable record of O. zeballosi in Uruguay, extending the species geographic distribution to its most southeastern boundary. This species, previously reported only from Entre Ríos and San Luis provinces in Argentina, increases the known macraucheniid diversity in the Neogene of Uruguay, which is currently under investigation.