Trinomys dimidiatus
Creators: name: Don E. Wilson
name: Thomas E. Lacher, Jr
name: Russell A. Mittermeier
Publisher: name: Lynx Edicions
Year: 2016
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Mammalia
Rodentia
Echimyidae
Trinomys
Trinomys dimidiatus

description: 21.
Rio de Janeiro Spiny-rat
Trinomys dimidiatus
French: Rat-épineux de Rio de Janeiro / German: Rio-de-Janeiroa-Atlantikstachelratte / Spanish: Rata espinosa atlantica
Other common names: Soft-spined Atlantic Spiny-rat, Atlantic Spiny-rat
Taxonomy. Echimys dimidiatus Gunther, 1877;
no type locality given. Identified by L. M. Pessoa and colleagues in 2015 as “Parque Nacional da Tijuca, Rio de Janeiro, Estado do Rio de Janeiro, Brasil.”
J. A. Allen transferred Gunther's dimidiatus to Proechimys in 1899, and J. Moojen placed it in the subgenus Trinomysin 1948; first use of current name combination stems from M. C. Lara and colleagues in 1996. Monotypic.
Distribution. SE Brazil, Rio de Janeiro State and N coastal border of Sao Paulo State.
Descriptive notes. Head-body 170-244 mm,tail 150-220 mm; weight 100-290 g. Dorsum of the Rio de Janeiro Spiny-rat is ocherous buff,finely lined with blackish brown, gradually becoming paler on sides and contrasting sharply with white venter. Bicolored tail is brownish above and white below, averaging 90% of head-body length;it lacks conspicuous pencil of elongated hairs at tip. Dorsal aristiforms are narrow and soft, imparting soft rather than spiny appearance to fur. Setiforms on mid-dorsum are whitish basally, gradually blackening toward tips but interrupted by an ocherous-full sub-distal zone; those on outer thighs are whitish on basal one-half and become gradually grayish in middle and light ocherous buff along distal one-third, often with blackish tips. Skull of the Rio de Janeiro Spiny-rat is elongated and slender, without conspicuous ridges, and averages 51-7 mm. Auditory bullae are small, smooth, elongated, and not inflated. The Rio de Janeiro Spiny-rat is uniquely distinguished from conspecifics by combination of lack of differentiated light-colored pelage on outerthighs, posteriorly wide incisive foramina with complete and columnar septum that is especially thick and wide across maxillary part, primarily squamosal contribution to post-orbital processes of zygoma, and karyotype with 2n = 60, FN = 116 that lacks dot-like supernumerary elements. Baculum is medium-sized, with average length of 7-6 mm, elongate and straight shaft with evenly rounded proximal and distal ends, and no distal wings.
Habitat. Atlantic Forest biome from sea level to elevations of ¢.1000 m. Typical habitat of the Rio de Janeiro Spiny-rat is the relatively open interior of climax evergreen forest characterized by sparse vegetation near the ground and marked middle layer comprised predominantly of species of Anonaceae, Melastomataceae, Myrsinaceae, and Rubiaceae under larger trees up to 30 m in height and covered with lianas and epiphytes. Individuals are commonly trapped in moist places and shelter or nest on the ground, usually under boulders, at bases of trees, or near fallen logs where litter accumulates, and typically close to water sources.
Food and Feeding. On Ilha Grande off the Rio de Janeiro, Rio de Janeiro Spiny-rats ate fruit and seeds of the invasive jackfruit tree, Artocarpus heterophyllus (Moraceae). Otherwise, they probably eat a variety of fruits, seeds, and insects.
Breeding. Breeding Rio de Janeiro Spiny-rats have been observed in March-May and September—-November. Litters have 1-5 young, most commonly two. Captive individuals survived for more than two years; one captive individual, already an adult when caught,lived for an additional 3-1 years.
Activity patterns. There is no specific information availablefor this species, but the Rio de Janeiro Spiny-rat is presumed to be primarily nocturnal.
Movements, Home range and Social organization. Adult pairs of males and females, sometimes with young, have been found in the same nest, suggesting monogamous mating system. Densities of Rio de Janeiro Spiny-rats on Ilha Grande coast were 1-19 ind/ha. Individuals exhibited territorial tendencies, and young and subadult individuals dispersed from natal areas.
Status and Conservation. Classified as Least Concern on The IUCN Red List. Population trends of Rio de Janeiro Spiny-rats are unknown, butit is regarded as locally common. A primary major threat would be continued deforestation, but Rio de Janeiro Spinyrats occur in several municipal, state, and federal reserves.
Bibliography. Allen (1899a), Davis (1945a, 1945b, 1947), Glinther (1877a), Lara et al. (1996), Mello et al. (2015), Moojen (1948), Pessoa, Tavares, de Oliveira & Patton (2015).
description: Published as part of Don E. Wilson, Thomas E. Lacher, Jr & Russell A. Mittermeier, 2016, Echimyidae, pp. 552-604 in Handbook of the Mammals of the World – Volume 6 Lagomorphs and Rodents I, Barcelona :Lynx Edicions on pages 563-564, DOI: 10.5281/zenodo.6623649