New record of Pampahippus secundus (Mammalia, Notoungulata) from the Upper Lumbrera Formation, Eocene of northwestern Argentina

Abstract

The Paleogene record of notoungulates in northwestern Argentina (NWA) is relatively abundant, including 20 species distributed in 16 genera (Powell et al., 2011; Babot et al., 2017). Fourteen of those 16 genera are recorded only in NWA (Powell et al., 2011; Woodburne et al., 2014b), the exceptions being Colbertia, also present in Itaboraí, Brazil, and Pseudhyrax, a typotherian found in the Argentinean Patagonia and central Chile (Paula Couto, 1952; Croft et al., 2003; Bergqvist et al., 2007). This fauna is not only restricted geographically but also temporally, given that only a few of these taxa have been recorded in more than one of the stratigraphic units cropping out in NWA (viz., Jujuy, Salta, Tucumán, and Catamarca provinces). Thus, most records correspond to single occurrences for each unit, preventing stratigraphic correlations, general comparisons for some fossil-bearing units, and the discovery of biogeographic patterns. Northwestern Argentinean genera are usually monotypic except Simpsonotus (two species; Pascual et al., 1978), Pampatemnus (two species; Vucetich and Bond, 1982), and Pampahippus (three species; Bond and López, 1993; Deraco and GarcíaLópez, 2016; García-López et al., 2017). The latter is remarkable because it is recorded in at least two formations, Lower Lumbrera and Quebrada de los Colorados, plus a dubious mention referred to cf. Pampahippus from the Geste Formation (López, 1997). Until now, the aforementioned stratigraphic units have no species in common, reinforcing the temporal and regional disjunct distribution of congeneric species (P. arenalesi and P. secundus for Lower Lumbrera, and P. powelli for Quebrada de los Colorados). Only sebecid crocodiles provide evidence of a temporally continuous lineage in these formations (Pol and Powell, 2011; Powell et al., 2011). During the last two years, new collecting efforts in MWA recovered a significant and varied amount of fossil vertebrates. We here present a new specimen referable to the ‘notohippid’ Pampahippus secundus from the Upper Lumbrera Formation at the locality of El Simbolar, Salta Province. This record provides new anatomical information for this taxon and expands its biochron from Lower Lumbrera to Upper Lumbrera, thereby being the first mammal common to both formations. We establish the sedimentological setting of this and previous fossils, describe the new specimen, and discuss its stratigraphic and biogeographic implications.