New remains of the dryolestoid mammal Leonardus cuspidatus from the Los Alamitos Formation (Late Cretaceous, Argentina)

Abstract

The great diversity of mammals from the Los Alamitos Formation (Campanian–Maastrichtian) in Rio Negro Province, Argentina has provided significant information about the evolution of South American dryolestoids. Among these mammals the alleged dryolestid Leonardus cuspidatus Bonaparte was described based on a fragment of maxilla with four molariforms. A right mandibular fragment with two molariforms from the same site as the maxilla is here assigned to L. cuspidatus. The lower molariforms are compatible in the expected morphology with those from the holotype. Even though referred to Dryolestidae, Leonardus shows unique features: (1) the presence of a huge and dome-like stylocone, disconnected and more centrally placed from the other cusps than in other dryolestoids such as Groebertherium, but contacting the preparacrista in the first preserved molar; (2) the absence of cingulae in both upper and lower molars, the latter being similar in shape to the former; (3) the presence of three roots in at least one of the lower molars, which has only been documented in the mesungulatid Coloniatherium for the m1. These characters confirm the diversity and uniqueness of the South American Mesozoic mammals.