The Wilfredomys pictipes [Rodentia: Sigmodontinae] karyotype with comments on the karyosystematics of Brazilian Thomasomyini

Karyotypic analysis of two specimens of Wilfredornys pictipes (Osgood, 1933), collected in the Atlantic forest of Sao Paulo State, Brazil, showed 2n = 36 / FN = 34. Comparative karyologic analysis indicated that W. pictipes was very different from species belonging to the tribe Oryzomyini and to the genus Delomys but similar to Rhipidomys species. These findings indicated that the tribe Thomasomyini is not a karyotypically homogeneous taxon. The low diploid number of W. pictipes is likely to be a derived trait among sigmodontine rodents.