Thylamys pusillus (Desmarest, 1804)

Russell A. Mittermeier & Don E. Wilson, 2015, Didelphidae, Handbook of the Mammals of the World – Volume 5 Monotremes and Marsupials, Barcelona: Lynx Edicions, pp. 129-186 : 178

84.

Chacoan Fat-tailed Opossum

Thylamys pusillus

French: Petit Opossum / German: Chaco-Fettschwanzbeutelratte / Spanish: Marmosa coligruesa del Chaco

Other common names: Austral Mouse Opossum, Chaco Fat-tailed Opossum, Chacoan Thylamys, Common Fat-tailed Mouse Opossum, Common Mouse Opossum, Small Fat-tailed Mouse Opossum, Small Fat-tailed Opossum

Taxonomy. Didelphis pusilla Desmarest, 1804 ,

type locality not given. Identified by Tate in 1933 as “ S. Ignacio , Misiones, Paraguay.”

This species is monotypic.

Distribution. SE Bolivia (Santa Cruz), W Paraguay (Alto Paraguay, Boqueron, Presidente Hayes, Nueva Asuncion), and N Argentina (Formosa).

Descriptive notes. Head-body 7-12 cm, tail 8.5-13.4 cm; weight 11-32 g. Dorsal fur of the Chacoan Fat-tailed Opossum is dark grayish or brownish gray mid-dorsally, with typical tricolored pattern of species of Thylamys , and markedly paler on bodysides. Head is colored as dorsum orslightly darker, but facial fur is paler, with distinct dark mid-rostral stripe. Narrow, dark eye-rings surround black eyes; paler shade extends forward toward nose without reaching it. Tail length is c¢.115% of head-body length, tail is markedly bicolored (dark dorsally and whitish ventrally), and it can become distinctly incrassated (enlarged with stored fat). Ventral fur is white or creamy from chin and cheeks to anus. Fur is short in mid-dorsum (7-9 mm long). Forefeet and hindfeet are small and whitish. Ears are large, naked, and reddish-brown. Females lack a pouch, and 15 mammae are present, seven on each side and a medial mamma. The Chacoan Fat-tailed Opossum has a 2n = 14, FN = 20 karyotype, with four pairs of biarmed and two pairs of acrocentric autosomes, and with a small biarmed X-chromosome. The Ychromosome is absent in somatic cells.

Habitat. Dry or seasonal thorn scrub or thickets of the Dry Chaco at elevations above 1000 m. Typical habitat of the Chacoan Fat-tailed Opossum has been described as xerophytic woodlands, with dominance of low, thorny, deciduous trees, including “quebracho” ( Schinopsis sp. and/or Aspidosperma quebracho-blanco, Apocynaceae ), “palo santo” ( Bulnesia sarmientoi, Zygophyllaceae ), “palo borracho” ( Ceiba insignis , Malvaceae ), and “labon” ( Tabebuia nodosa, Bignoniaceae ), and typical understory with “algarrobo” ( Prosopis , Fabaceae ), Maytenus (Celastraceae) , Mimosa (Fabaceae) , Ephedra (Ephedraceae) , cacti, and spiny bromeliads. The neotype was collected in a location described as “dense, thorny vegetation that included quebracho, palo santo, palo borracho, and several species of cacti; however, a small, apparently natural grassy opening was also adjacent to the trap site.”

Food and Feeding. Arthropods are the most common item in the diet of the Chacoan Fat-tailed Opossum, but fruits, seeds, and leaves are also consumed.

Breeding. There is no information available for this species.

Activity patterns. There is no information available for this species.

Movements, Home range and Social organization. The neotype of the Chacoan Fattailed Opossum was caught on the ground, but other specimens were captured on the ground and in traps set at a height of up to 1 m in trees and shrubs.

Status and Conservation. Classified as Least Concern on The IUCN Red List. The Chacoan Fat-tailed Opossum has a wide distribution and presumably a large overall population, but deforestation in the Chaco region of Paraguay might lead to decreases in its population sizes.

Bibliography. Abdala et al. (2006), Braun, Mares & Stafira (2004), Braun, Van Den Bussche et al. (2005), Campos et al. (2001), Carmignotto & Monfort (2006), Creighton & Gardner (2007c¢), Flores et al. (2000), Giarla et al. (2010), Palma & Yates (1996), Palma, Boric-Bargetto et al. (2014), Palma, Rivera-Milla et al. (2002), Smith (2009d), Solari (2003), Tate (1933), Teta, D'Elia et al. (2009), Voss, Myers et al. (2009).

Figures

76. Patagonian Opossum (Lestodelphys halli), 77. Karimi’s Fat-tailed Opossum (Thylamys karimii), 78. Dwarf Fat-tailed Opossum (Thylamys velutinus), 79. Elegant Fat-tailed Opossum (Thylamys elegans), 80. Pallid Fat-tailed Opossum (Thylamys pallidior), 81. Tate's Fat-tailed Opossum (Thylamys tatei), 82. Mesopotamian Fat-tailed Opossum (Thylamys citellus), 83. Dry Chaco Fat-tailed Opossum (Thylamys pulchellus), 84. Chacoan Fat-tailed Opossum (Thylamys pusillus), 85. Paraguayan Fat-tailed Opossum (Thylamys macrurus), 86. Argentine Fat-tailed Opossum (Thylamys sponsorius), 87. Buff-bellied Fat-tailed Opossum (Thylamys venustus), 88. Bishop's Slender Opossum (Marmosops bishop), 89. Junin Slender Opossum (Marmosops juninensis), 90. Delicate Slender Opossum (Marmosops parvidens), 91. Pantepui Slender Opossum (Marmosops pakaraimae), 92. Pinheiro’s Slender Opossum (Marmosops pinheiroi), 93. Handley’s Slender Opossum (Marmosops handleyi), 94. Gray Slender Opossum (Marmosops incanus), 95. Brazilian Slender Opossum (Marmosops paulensis), 96. Neblina Slender Opossum (Marmosops neblina), 97. Tschudi’s Slender Opossum (Marmosops impavidus), 98. Spectacled Slender Opossum (Marmosops ocellatus), 99. Creighton’s Slender Opossum (Marmosops creightoni), 100. White-bellied Slender Opossum (Marmosops noctivagus), 101. Narrow-headed Slender Opossum (Marmosops cracens), 102. Dusky Slender Opossum (Marmosops fuscatus), 103. Panama Slender Opossum (Marmosops invictus)

Distribution. SE Bolivia (Santa Cruz), W Paraguay (Alto Paraguay, Boqueron, Presidente Hayes, Nueva Asuncion), and N Argentina (Formosa).