Thrichomys

Rocha, Rita G., Ferreira, Eduardo, Costa, Barbara M. A., Martins, Iracy C. M., Leite, Yuri L. R., Costa, Leonora P. & Fonseca, Carlos, 2011, Small mammals of the mid-Araguaia River in central Brazil, with the description of a new species of climbing rat, Zootaxa 2789, pp. 1-34 : 29-30

Thrichomys sp.

Identification. Thrichomys sp. was recently recognized as distinct from the described species of the genus based on karyotypic and phylogenetic analyses ( Bonvicino et al. 2002, Braggio & Bonvicino 2004). Our phylogenetic analyses allow us to assign the specimens collected from mid-Araguaia River basin to Thrichomys sp. of Braggio and Bonvicino (2004) ( Fig. 18 ). Specimens of Thrichomys sp. from the states of Tocantins (UFES 1407 and RGR 353) and Goiás (MN 66132 and MN 50177, Braggio & Bonvicino 2004) form a monophyletic group (BPP = 0.99), with an average divergence of 2% among them. The clades of T. apereoides , T. pachyurus and T. inermis correspond to those of Braggio and Bonvicino (2004), but well-supported interspecific relationships are not recovered by our phylogenetic analyses.

Bezerra et al. (2009) provide brief comments on the external morphology of Thrichomys sp., but no craniodental characters have been published for this species. Externally, it has brown dorsal pelage streaked with black hairs and soft fur; body sides are lighter than the dorsum and there is no lateral line limiting the whitish gray ventral pelage. Forehead is lighter than the dorsum and there are two white spots, one below and one above the eye. Ears are covered by white thin hairs and have a white spot at the base. The hairy tail is shorter than head and body and covered by dark hairs dorsally and white hairs ventrally. Fore and hind feet are whitish gray above and have dorsal dark marks on the metatarsi. Claws are covered by long ungual hairs.

The skull of Thrichomys sp. is small and strongly built ( Fig. 19 ). The rostrum is relatively short; the interorbital region converges anteriorly and has well developed supraorbital crests. The floor of the infraorbital foramen has a well developed lateral flange. The incisive foramen is broad and oval shaped; the palate is grooved and the mesopterygoid fossa is V-shaped extending to anterior edge of M3. Premolar and M3 are smaller than M2 and M3. Upper molariforms have two labial and one lingual counterfolds; lower molars have the reverse pattern of the upper molars, and the lower premolar has one labial and three lingual counterfolds.

Measurements (n = 5): HB = 174–210, T = 121–145, HF = 40–44, E = 23–24, W = 223–263.

Distribution. This species occurs throughout the Tocantins River basin, extending to the Paraná River basin in central Brazil ( Braggio & Bonvicino 2004).

Natural history. Five adult specimens (two males and three females) were captured on the ground in Tomahawk and Sherman traps. These captures occurred in a dry and open area of Cerrado with dense grasses (campo sujo) and several termite mounds. One female collected in May 2008 had two embryos. Two additional skulls of Thrichomys sp. were found inside a water reservoir.

Vouchers (n = 6: 2ɗ 2Ψ 2 skulls): UFES 1406–1411.

Figures

FIGURE 18. Bayesian tree of cyt-b haplotypes from specimens of Thrichomys, rooted using Trinomys and Makalata. Bayesian posterior probabilities are in bold and percentages are average Kimura two-parameter distances.

FIGURE 19. Dorsal, ventral and lateral views of skull and mandible of Thrichomys sp. (male, UFES 1407).