History
Most of the Brazilian members of the genus ''Necromys'' were Species description, first described in the second half of the nineteenth century, and the species from the Andes followed in the first decades of the twentieth century. Small rodents in South America were studied by the British zoologist Oldfield Thomas, curator at the Natural History Museum, London who erected the genus ''Bolomys'' in 1916.Characteristics
Members of the genus ''Necromys'' are spread out over a wide area of Central and South America. Morphologically, members of the genus are difficult to distinguish from two other genera found in the same region, the grass mice ''Akodon'' and the cane mice ''Zygodontomys''. In 1987, the Argentine zoologist Osvaldo Reig listed the characteristics that distinguished the genus ''Bolomys'' from ''Akodon'' as; the braincase is broad and deep; the occipital region is short; the rostrum is fairly short; the rostrum tapers forwards when viewed from the side; the occiput is short and truncated; the zygomatic plate is broad, with the front edge straight or slightly concave; the upper incisors are orthodont or proodont; the molars are mesodont, broad and robust; the upper molars have transverse loops; and the lower molars have the lingual cusps slightly in front of the labial cusps. There is very little variation in the karyotype of ''Necromys'', where 2n=34 is the rule, with ''N. lactens'' and ''N. lasiurus'' having diploid numbers of 2n=36. This is in great contrast to the explosively radiating ''Akodon'' which has ploidy, diploid numbers ranging from 2n=14 to 2n=52.Species
Species listed in ''Necromys'' include: * ''Pleasant bolo mouse, N. amoenus'' Pleasant bolo mouse * ''Argentine bolo mouse, N. benefactus'' Argentine bolo mouse * ''Rufous-bellied bolo mouse, N. lactens'' Rufous-bellied bolo mouse * ''Hairy-tailed bolo mouse, N. lasiurus'' Hairy-tailed bolo mouse * ''Paraguayan bolo mouse, N. lenguarum'' Paraguayan bolo mouse * ''Necromys lilloi, N. lilloi'' * ''Dark bolo mouse, N. obscurus'' Dark bolo mouse * ''Spotted bolo mouse, N. punctulatus'' Spotted bolo mouse * ''Temchuk's bolo mouse, N. temchuki'' Temchuk's bolo mouse * ''Northern grass mouse, N. urichi'' Northern grass mouse * †''Necromys bonapartei, N. bonapartei'', Monte Hermoso Formation (Montehermosan)References
{{portalbar, Mammals, Animals, Biology Necromys, Rodent genera