New Leontiniid Notoungulata (Mammalia) from Chile and Argentina: Comparative Anatomy, Character Analysis, and Phylogenetic Hypotheses

Abstract

Herein we describe and name two new species of leontiniid notoungulates, one being the first known from Chile, the other from the Deseadan South American Land Mammal Age (SALMA) of Patagonia, Argentina. Te Chilean leontiniid is from the lower horizons of the Cura-Mallín Formation (Tcm1) at Laguna del Laja in the Andean Main Range of central Chile. Tis new species, Colpodon antucoensis, is distinguishable from Patagonian species of Colpodon by way of its smaller I2; larger I3 and P1; sharper, V-shaped snout; and squarer upper premo- lars. Te holotype came from a horizon that is constrained below and above by 40Ar/39Ar ages of 19.53 ± 0.60 and 19.25 ± 1.22, respectively, suggesting an age of roughly 19.5 Ma, or a little older (~19.8 Ma) when corrected for a revised age of the Fish Canyon Tuff standard. Either age is slightly younger than ages reported for the Colhuehuapian SALMA fauna at the Gran Bar- ranca. Taxa from the locality of the holotype of C. antucoensis are few, but they (e.g., the mylo- dontid sloth, Nematherium, and a lagostomine chinchillid) also suggest a post-Colhuehuapian