Comparative analysis of Galea (Rodentia, Caviidae) and expanded diagnosis of Galea ortodonta Ubilla and Rinderknecht, 2001 (Late Pleistocene, Uruguay)

Abstract

The family Caviidae is a diverse group of South American caviomorph rodents with many living and extinct taxa. Paleontological information about the caviid genus Galea is scant; only two extinct species have been described from fragmentary material so far. Recently, complete skulls and mandibles of the extinct Galea ortodonta have been found (Dolores Fm., Late Pleistocene; Santa Lucía river basin, southern Uruguay). Based on anatomical and quantitative analyses, we provide an expanded diagnosis and description of G. ortodonta, which thus becomes the best-known extinct species of the genus, accompanied by a critical assessment of skull, mandible and dental characters at the generic level. The wide intra-specific variability observed in several characters makes difficult to identify exclusive characters at the species level and to describe species based on fragmentary materials or on mandibles alone. G. ortodonta is characterized by the following associated features: large size; orthodont upper incisor; latero-external face of the incisors with extended enamel; small and laterally compressed auditory bullae; wide basioccipital; maxillary zygomatic process with apophysis; upper cheek teeth with external primary and secondary folds; palatine wide at the mesopterygoid fossa; and horizontal mandibular crest starting at p4. This character association differs from all other living and extinct species of the genus but resembles the G. musteloides species group to some extent. Biostratigraphic information and absolute ages support a Late Pleistocene age for the new material and a correlation with the late phases of Marine Isotope Stage MIS3. Galea occupied lowland areas in southern Uruguay during the Late Pleistocene and, like other associated mammals, suggests open or semi-open areas with an arid or semi-arid context, an environmental scenario arguably influenced by the late phases of MIS3.