''Necromys'' is a genus of South American sigmodontine

rodent Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are roden ...

s allied to ''

Akodon ''Akodon'' is a genus consisting of South American grass mice. They mostly occur south of the Amazon Basin and along the Andes north to Venezuela, but are absent from much of the basin itself, the far south of the continent, and the lowlands west ...

''. This genus has also been known as ''Cabreramys'' or more recently ''Bolomys'', and the northern grass mouse (''N. urichi'') has recently been transferred from ''Akodon''.

History

Most of the Brazilian members of the genus ''Necromys'' were 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 The Natural History Museum in London is a museum that exhibits a vast range of specimens from various segments of natural history. It is one of three major museums on Exhibition Road in South Kensington, the others being the Science Museum ...

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 ''

'' and the cane mice ''

Zygodontomys ''Zygodontomys'' is a genus of rodent in the tribe Oryzomyini of the family Cricetidae. Its closest relative may be ''Scolomys''. It ranges from Central America east to the Guianas. It contains two species: ''Zygodontomys brunneus'' and ''Zyg ...

''. 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 A karyotype is the general appearance of the complete set of metaphase chromosomes in the cells of a species or in an individual organism, mainly including their sizes, numbers, and shapes. Karyotyping is the process by which a karyotype is disce ...

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 diploid numbers ranging from 2n=14 to 2n=52.

Species

Species listed in ''Necromys'' include: * '' N. amoenus'' Pleasant bolo mouse * '' N. benefactus'' Argentine bolo mouse * '' N. lactens'' Rufous-bellied bolo mouse * '' N. lasiurus'' Hairy-tailed bolo mouse * '' N. lenguarum'' Paraguayan bolo mouse * '' N. lilloi'' * '' N. obscurus'' Dark bolo mouse * '' N. punctulatus'' Spotted bolo mouse * '' N. temchuki'' Temchuk's bolo mouse * '' N. urichi'' Northern grass mouse * †'' N. bonapartei'', Monte Hermoso Formation (

Montehermosan The Montehermosan age is a period of geologic time (6.8–4.0 Ma) within the Miocene and Pliocene epochs of the Neogene used more specifically with South American Land Mammal Ages. It follows the Huayquerian and precedes the Chapadmalalan The C ...

)Farola Monte Hermoso FI Facies
at

Fossilworks Fossilworks is a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database, a large relational database assembled by hundreds of paleontologists from around the world. History Fossilworks was cre ...

.org

References

{{Taxonbar, from=Q139082 Rodent genera