Mesotheriid (Mammalia, Notoungulata) remains from the Colhuehuapian beds (Early Miocene) of Chichinales Formation, Río Negro Province, Argentina

Abstract

The Mesotheriidae represent one of several clades of the endemic South American ungulate Order †Notoungulata. This clade has some rodent-like adaptations such as hypertrophied upper and lower incisors, highly hypsodont cheek teeth, reduced dental formula (in younger forms), simplified occlusal morphology, and specialized zygomasseteric structure, among other features (Patterson, 1934; Billet et al., 2008). Traditionally, the Mesotheriidae have been divided into two subfamilies: Trachytheriinae and Mesotheriinae (Simpson, 1945). Recent phylogenetic analyses supported the monophyly of Mesotheriinae, but indicated that Trachytheriinae is a paraphyletic assemblage of basal mesotheriids (Cerdeño and Montalvo, 2001; Croft et al., 2004; Reguero and Castro, 2004; Billet et al., 2008).