Taxonomy and distribution of the sigmodontine rodents of genus Necromys incentral Argentina and Uruguay

The taxonomic status of the species of Necromys Ameghino, 1889 (= Bolomys T homas, part), inhabiting the pampean region of Argentina and southern Urugu ay is not clear. The two most recent systematic hypotheses both distinguish two species. Massoia and Fornes (1967) recognized Necromys obscurus (Water house, 1837) with allopatric populations in southern Uruguay and southeaste rn Buenos Aires Province (Argentina), and N. benefactus (Thomas, 1919) dist ributed in a strip across northwestern-southwestern Buenos Aires Province. Reig (1987) argued that the populations of Uruguay and northwestern Buenos Aires Province belong to N. obscurus (including N. benefactus as a subspeci es), while those of the southeast and southwest are referred to an unnamed taxon. To solve this problem, 152 specimens from Argentina and Uruguay were studied using morphometric data and qualitative characters. Craniodental v ariables were measured in 97 adult specimens of both sexes. Discriminant-fu nction analysis among preestablished geographic groups and cluster analysis using Mahalanobis distances revealed the presence of two groups with contr asting morphological characteristics. The first group, which corresponds to N. benefactus, includes the populations from northern La Pampa, southern S anta Fe, and northwestern, central west, and southwestern Buenos Aires Prov ince (Argentina). The second group, N. obscurus, includes the populations f rom Uruguay (N. obscurus obscurus) and from southeastern Buenos Aires Provi nce (a new subspecies).