16. Western Amazonian Mouse Opossum Marmosa macrotarsus French: Opossum macrotarse / German: Grof 3ful3-Zwergbeutelratte / Spanish: Marmosa amazonica Taxonomy. Didelphys macrotarsus Wagner, 1842, type locality not given. Restricted by J. A. Wagner in 1847 to Rio Madeira, Brazil. Formerly considered a subspecies of M. munrina. As treated here, this species now includes M. quichua as a synonym. Bolivian specimens (La Paz, Santa Cruz, Beni) formerly attributed to M. murina not examined, but are provisionally assigned to this species. Monotypic. Distribution. W of Amazonian Brazil (S of Amazon River and W of Tapajés River) to Amazonian Peru (S of Amazon and Maranon rivers), and probably Bolivia. Descriptive notes. Head—body 10.4-13.6 cm,tail 14.8-20.6 cm; weight 23-51 g. Dorsal fur of the Western Amazonian Mouse Opossum is grayish-brown, variably washed with orangish-brown and slightly paler on body sides. Head fur is paler than on dorsum and lacks any mid-rostral stripe; there are dark brown eye-rings surrounding black eyes, and rings do not reach base of ears. Tail length is c.145% of head-body length, and tail is furred on proximal 10% and is brown on naked part. Tail is usually paler on ventral side and sometimes unpigmented on distal one-third. Ventral fur has a median streak of yellowish or creamy-white hair, usually narrower on chest and abdominal and inguinal regions, which are flanked by bands of gray-based yellowish or bufty or orangish fur, usually on sides of chest, abdomen, and inguinal region, but also occurring on sides of throat and ventral portion of limbs. Throat gland is absent. Feet are whitish to orangish brown. Females lack a pouch and have eleven mammae, five on each side and an additional medial mamma. The Western Amazonian Mouse Opossum has a 2n = 14, FN = 24 karyotype, with all biarmed autosomes, and a biarmed X-chromosome and an acrocentric Y-chromosomes. Habitat. [Lowland or montane wet tropical forests at elevations of 25-1900 m. In western Brazilian Amazon, the Western Amazonian Mouse Opossum has been trapped in terra firma forest and between terra firma and igap6 (seasonally inundated black-water) forest. Food and Feeding. There is no information available for this species. Breeding. Females caught in October and May in the western Brazilian Amazon were not lactating and did not have any attached young. Activity patterns. There is no information available for this species. Movements, Home range and Social organization. In the western Brazilian Amazon, Western Amazonian Mouse Opossums were trapped only on the ground, but in the Peruvian Amazon, they seemed to spend equal amounts of time on and above the ground. Status and Conservation. The Western Amazonian Mouse Opossum has not yet been assessed as a distinct species on The IUCN Red List. At the time of the last assessment, it was considered a subspecies of Linnaeus’s Mouse Opossum (Marmosa murina). Conservation status of all opossumsis being reassessed by the IUCN New World Marsupial Specialists Group. Bibliography. Faria, de Oliveira & Bonvicino (2013), Gutiérrez et al. (2010), Patton et al. (2000), Reig et al. (1977), Rossi (2005), Voss et al. (2014), Wagner (1847), Woodman etal. (1995).

Published as part of Astúa, D., 2015, Didelphidae, pp. 129-186 in Handbook of the Mammals of the World – Volume 5 Monotremes and Marsupials, Barcelona :Lynx Edicions on page 140, DOI: 10.5281/zenodo.6685333