Austropediomys marshalli?gen. et sp. nov., a new Pediomyoidea (Mammalia, Metatheria) from the Paleogene of Brazil: paleobiogeographic implications

摘要

The Pediomyiodea has been largely regarded as a Late Cretaceous North American metatherian lineage; however, some studies have suggested that a few South American taxa could be related to this family. Herein, Austropediomys marshalli gen. et sp. nov. from the Itaborai Basin, Brazil (lower Eocene — Itaboraian SALMA), is described. Austropediomys gen. nov. represents the first report of a pediomyoid metatherian in the Paleogene of South America backed by a phylogenetic analysis. Several derived features in the upper molars support its belonging to the Pediomyoidea: presence of accessory ‘conular-like’ structures (here named conuloids) lingual to the conules; supernumerary stylar cusps; asymmetric stylar shelf, with parastylar shelf reduced to a narrow rim in M1; straight centrocrista; short and obliquely oriented prepacrista, which contacts StA in M2-3. The presence of ‘conular-like’ structures lingual to the paraconule and metaconule is identified in Austropediomys gen. nov. and in Late Cretaceous pediomyoids as well, and results in the phylogenetic analysis as a synapomorphy of the Pediomyoidea. Austropediomys gen. nov. is autapomorphyc in the presence of enlarged conuloids on protocristae. The record of a pediomyoid in the Paleogene of South America increases the temporal and biogeographical range of this lineage. Also, our results support the hypothesis that several non-related metatherian lineages dispersed from North to South America via the Caribbean Plate, most probably during the latest Cretaceous, in an island-hopping or sweepstakes model.