Sexual dimorphism in living and fossil plains viscachas (Rodentia, Caviomorpha, Chinchillidae) of Argentina: a qualitative approach.

RASIA, CANDELA Y FLORES

Congreso; IV Congreso Latinoamericano de Paleontología de Vertebrados; 2011

Despite being one of the most sexually dimorphic living rodents, there have been few morphological studies of sexual dimorphism of the plains viscacha, Lagostomus maximus (Desmarest, 1817). We compared the skull morphology of adult males and females of this species in order to recognize anatomical characters that allow discriminating adults of each sex. Preliminary results indicate differentiation between adult males and females in several skull features such as: 1- development and length of temporal and sagittal crests, 2- length of the parietals in relation to their width, 3- size of the area of origin of the temporal muscles. The morphology observed in adult males of the living species was also identified in fossil specimens of Lagostomus maximus (Holocene of Buenos Aires Province), Lagostomus cavifrons Ameghino, 1889 (Pleistocene of Buenos Aires and Santa Fe Provinces) and Lagostomus (Lagostomopsis) incisus (Ameghino, 1888) (Pliocene of Buenos Aires Province). The possible presence of sexual dimorphism in a Pliocene species of Lagostomus Brookes, 1828 suggests that social behaviors such as polygyny (males mating with multiple females) and male-male competition, both related to male-biased sexual size dimorphism and observed in the living L. maximus, were already established in the genus by that time. This evidence is also important for interpreting the systematics of Neogene chinchillids.