543.

Blackish Grass Mouse

Thaptomys nigrita

French: Akodon noiratre / German: Schwarze Grasmaus / Spanish: Raton de hierba negruzco

Other common names: Ebony Akodont

Taxonomy. Mus nigrita Lichtenstein, 1829, vicinity of Rio de Janeiro, Rio de Janeiro, Brazil.

Hesperomys subterraneus named by R. Hensel in 1873 (= Mus nigrita Lichtenstein, 1829) is the type species of the genus Thaptomys named by O. Thomas in 1916. Extensive morphological, karyologycal and molecular variation was found in this genus. Possibility that 7. nigrita might be composite of two or more species thus remains an open question. Monotypic.

Distribution. E, SE & S Brazil, SE Paraguay, and NE Argentina (Misiones Province).

Descriptive notes. Head-body 83-99 mm, tail 30-50 mm, ear 10-12 mm, hindfoot 16-20 mm; weight 18-27 g. The Blackish Grass Mouse is small akodont-like sigmodontine. Fur is velvety and short; eyes are very small; ears are short; and tail is short, usually equal to or less than 50% of head-body length, and very thinly haired short stiff hairs brown above, whitish below, not concealing scales. Dorsum is dark brown or glistening olive-brown to reddish brown, finely grizzled with ocherous brown and intermixed with some longer blackish brown hairs. Underparts are ocherous to dull brownish gray washed with buff, and hairs are dark slaty at their bases. Manual claws are long and fine; pedal claws are shorter. Palms and soles are naked, with prominent pads. Females have 3—4 pairs of mammae.

Habitat. Primary and second growth forest and grasslands near forests in the Atlantic Forest ecoregion. Blackish Grass Mice typically inhabit logs and tree roots but also woodpiles and cleared cultivated fields in forested regions. They selected sites with a greater amount of small woody debris in cool-dry season, but in warm-wet season, they mainly were found in area with high arthropod biomass.

Food and Feeding. Stomach contents of Blackish Grass Mice suggest a diet of plant matter and arthropods.

Breeding. Female Blackish Grass Mice with open vaginas were caught in April-May and September—October; males with descended testes were caught in May and October. Breeding in April-May is consistent with trapping ofjuveniles in May—August. Litters have 3-5 young.

Activity patterns. The Blackish Grass Mouse is mostly diurnal.

Movements, Home range and Social organization. The Blackish Grass Mouse is adapted for semi-fossorial life. It makes tunnels in leaf litter or in soft earth. Several specimens were collected with a single trap in a small area on consecutive days, suggesting some degree of sociality or gregariousness, or at least that a single burrow system is used by more than one individual. The Blackish Grass Mouse vanished almost always underneath foliage immediately after release; more than 40% of all movements did not exceed 20 m.

Status and Conservation. Classified as Least Concern on The IUCN Red List.

Bibliography. Caceres (2004), Davis (1947), Hensel (1873), Hershkovitz (1998), de Lima et al. (2010), Massoia (1963a), Moreira & Oliveira (2011), Myers & Wetzel (1979), Naxara et al. (2009), Patton et al. (2008), Pinotti et al. (2011), Puttker et al. (2006), Reig (1987), Silva (2008), Teta, Pardinas & D'Elia (2015¢c), Thomas (1916d), Ventura, Silva, Fagundes et al. (2004), Ventura, Silva & Yonenaga-Yasuda (2010).