Prolagostomus amplus Ameghino is a Junior Synonym of the Patagonian Rodent Pliolagostomus notatus Ameghino (Chinchillidae; Early Miocene, Santa Cruz Formation)

Abstract

Chinchillidae is a group of caviomorph rodents that includes the extant Chinchilla, Lagidium and Lagostomus. The latter genus, with a single living species (Lagostomus maximus), is grouped in the subfamily Lagostominae together with the extinct Eoviscaccia (Early Oligocene-Early Miocene), Prolagostomus (Early-Middle Miocene) and Pliolagostomus (Early-Middle Miocene). The Lagostominae are represented in the Santa Cruz Formation (late Early Miocene of Santa Cruz Province, Argentina) by Pliolagostomus notatus and eight species of Prolagostomus. One of these species of Prolagostomus, “Prolagostomus amplus”, was originally characterized by having all lower cheek teeth of the same size. The holotype and referred material of “Prolagostomus amplus” do not show some of the characters commonly used to distinguish Prolagostomus from other lagostomines (e.g. molars with sinuous hypoflexus/hypoflexid, anterior and lingual face of the lower molars not forming a marked angle, laminar third lobe of the M3 posteriorly or posterolingually oriented), instead, they share with Pliolagostomus notatus the presence of straight hipoflexus/hipoflexid in all cheek teeth, anterior and lingual face of the lower molars forming a marked angle, third lobe of the M3 subtriangular and lingually oriented, mental foramen dorsolaterally located. Therefore, we consider that “Prolagostomus amplus” is a synonym of Pliolagostomus notatus.