The Metatheria from the Río Santa Cruz (Santa Cruz Formation, Early-Middle Miocene, Argentina): History and new records

Abstract

Here we summarize the species of Metatheria from the Early-Middle Miocene Santa Cruz Formation at the Río Santa Cruz (RSC; Argentina). We assign newly collected specimens from the RSC localities Barrancas Blancas (BB) and Segundas Barrancas Blancas (SBB) to the known metatherian species. The metatherians from RSC were first described by F. Ameghino in 1887. He did not always establish clearly the type specimens of the species he founded, and often later he chose new type specimens. This led to confusion by future authors when they assumed they were looking at the original types when in fact they were the substitutes. We evaluated the actual and supposed type specimens from the RSC. We have identified the holotype of the Paucituberculata Palaeothentes aratae Ameghino and its calcotype. Following the International Code of Zoological Nomenclature (Art. 75), we formally propose neotypes, for the species Sipalocyon gracilis Ameghino (Sparassodonta) and for Microbiotherium patagonicum Ameghino (Microbiotheria). The species Perathereutes pungens Ameghino (Sparassodonta), previously known only from coastal localities, is described for the first time for the RSC. In total, we recognized 16 metatherian species for the RSC: seven Paucituberculata, seven Sparassodonta, and two Microbiotheria. Ten of the 16 species were recorded from recent fieldtrips. All 10 are recorded from SBB, six come from BB, and none from a third RSC locality, Yaten Huageno.