Rhipidomys ipukensis, Rocha, Rita G., Ferreira, Eduardo, Costa, Barbara M. A., Martins, Iracy C. M., Leite, Yuri L. R., Costa, Leonora P. & Fonseca, Carlos, 2011

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 : 24-27

Rhipidomys ipukensis n. sp. Rocha, B. M. A. Costa and L. P. Costa

Holotype. An adult male consisting of skin, skull and mandible collected on 24 July 2008 by Rita G. Rocha, under original field number RGR 452, and deposited at Museu Nacional, Universidade Federal do Rio de Janeiro, Brazil, under collection number MN 73741. A liver tissue sample preserved in ethanol is stored at Coleção de Tecidos e DNA da Universidade Federal do Espírito Santo.

Paratypes. Three paratypes were deposited at Museu Nacional, Universidade Federal do Rio de Janeiro (MN 73742–73744), two adult males, and a juvenile male, under original field numbers RGR 410, 412 and 184, respectively. Other three paratypes were deposited at Coleção de Mamíferos da Universidade Federal de Espírito Santo ( UFES 1449–1451), two adult females and an adult male, under original field numbers RGR 399, 403 and 411, respectively. Paratypes consisting of skin, skull, mandibles and liver tissue sample preserved in ethanol, were collected at the type locality, with exception of the juvenile male that was collected at Parque Estadual do Cantão.

Type locality. Fazenda Lago Verde, municipality of Lagoa da Confusão, state of Tocantins, Brazil, 10º52’09.1”S, 49º41’52.1”W, elevation 180 m. This 8,000 ha private farm is located along the Urubu and Lago Verde Rivers. About 30% of the area is used for agricultural activities and the remaining is still unexploited and covered with pristine Cerrado sensu lato physiognomies. Both agricultural and Cerrado areas have natural forest fragments, locally called ipucas ( Martins et al. 2002), which are dominated by plant species belonging to the families Favaceae, Arecaceae , Chrysobalanaceae and Vochysiaceae ( Martins et al. 2008) . The holotype and five paratypes of Rhipidomys ipukensis n. sp. were captured in these fragments.

Diagnosis. A medium-sized Rhipidomys species with dorsal pelage yellowish gray-brown to orangish brown and ventral pelage cream. The tail is moderately longer than head and body length with a medium-sized terminal pencil; hind feet are broad and have dark dorsal markings limited to metatarsals; ears are large ( Table 3 ). The skull is medium-sized, with relatively shallow zygomatic notches viewed from above; the interorbital region is convergent anteriorly with beaded supraorbital margins ( Fig. 14 ); it has pattern 3 of carotid circulation (sensu Voss 1988); the subsquamosal foramen is small, almost occluded by the long hamular process; the incisive foramen is bulletshaped and its margins are posteriorly parallel to each other; and the mesopterygoid fossa is M-shaped and its margins are parallel-sided ( Fig. 15 ).

Description. This is a medium-sized species, with adult head and body length varying from 99 to 141 mm. The tail is 114–124% longer than head and body. The dorsal pelage is relatively short with coarse texture, and it varies from yellowish gray-brown to orangish brown. Dorsal fur is gray-based with yellowish to orangish tips mixed with completely black guard hairs. Body sides are lighter than the dorsum and have a well-defined limit with venter. The ventral pelage is woolly, and it varies from whitish to cream; some specimens have a dark cream ventral midline.

Females have three pairs of mammae. Juveniles have completely light gray dorsal pelages and white ventral pelages. The tail is completely dark gray and is covered with short hairs along the anterior half of the tail. These hairs become longer along the posterior half, ending in a medium-sized pencil up to 10 to 15 mm in length. Hind feet are broad and have dark dorsal metatarsal markings that vary from narrow and flanked by white fur, to broad with poorly defined lateral limits. Ungual hairs are white and completely cover the claws, not passing beyond them. Ears are large ( Table 3 ) and brown, and in some specimens have a small cream patch of fur at the base of the ear.

Rhipidomys ipukensis n. sp. Rhipidomys emiliae Rhipidomys nitela

Measures Mean ± SE Range n Mean ± SE Range n Mean ± SE Range n The skull varies from small and more delicate in younger specimens to medium-sized and more robust in older specimens. The rostrum is moderately long and zygomatic notches are relatively shallow, although visible in dorsal view ( Fig. 14 ). The interorbital region converges anteriorly and has beaded supraorbital margins. The braincase is large and rounded. The zygomatic plate is broad and its posterior margin is anterior to the alveolus of M1. The alisphenoid strut is present and the subsquamosal foramen is small, almost occluded by the long hamular process. It has the pattern 3 of carotid circulation (sensu Voss 1988) with small stapedial foramen, no squamosal-alisphenoid groove and no sphenofrontal foramen. The palatal bridge is short and wide, and the incisive foramen is bulletshaped and its margins are parallel to each other posteriorly, reaching the anterior edge of M1. The mesopterigoyd fossa is M-shaped and extends to the mid-line of the last molars. Posterior palatal pits are a simple and small perforation present on each side of the mesopterigoyd fossa or, in some specimens, two small perforations on one side of mesopterigoyd fossa. Sphenopalatine vacuities are either present as small slits, or absent if the mesopterigoyd roof is completely ossified. Bullae are small. Upper incisors are opisthodont. M1 has labial accessory root, and m1 has labial and lingual accessory roots. Anterocone/conid of upper and lower molars are divided in two conules/lids by the anteromedian flexus/flexid. Oblique paralophules are present in all upper molars and are relatively reduced in size, and the posterior part of M3 is reduced. The mental foramen opens laterally on the body of mandible and the capsular process of lower incisor alveolus is well developed as a conspicuous swelling.

Comparisons. This species is similar to sympatric Oecomys species, but its distinct tufted tail and dark patch on the hind feet allow recognition of these two cricetid genera in the field. When compared to congeners, R. ipukensis n. sp. is intermediate in size relative to R. emiliae and R. nitela : it has smaller head-body and tail than the former and a slightly longer than the latter. Ears of R. ipukensis n. sp. are larger than those of R. emiliae and R. nitela ( Table 3 ). The dorsal coloration is also distinct from specimens of R. nitela from the Guianas, which are more reddish. Specimens of R. emiliae have grayish dorsal pelages and R. ipukensis n. sp. is more yellowish to orangish gray-brown.

Our series of R. ipukensis n. sp. was compared to seven specimens of R. emiliae from Serra do Carajás, state of Pará, Brazil, and despite sharing almost all cranial characteristics, some characters allow the distinction between these two species. The skull of R. emiliae is larger than R. ipukensis n. sp. for specimens of the same dental age class; the subsquamosal foramen is larger in R. emiliae , while in R. ipukensis n. sp. it is almost occluded by the hamular process; the incisive foramen of R. emiliae is elliptical in shape, and broader in the median part, contrasting to a more parallel-sided incisive foramen of R. ipukensis n. sp.; the mesopterigoyd fossa of R. emiliae is broader anteriorly ( Fig. 15 ). We also compared the skull of R. ipukensis n. sp. to eleven specimens of R. nitela from Guyana and French Guiana. The main distinctions between these two species are the smaller size, the teardropshaped incisive foramen, and the anteriorly broader mesopterigoyd fossa of R. nitela . When R. ipukensis n. sp. was compared to R. macrurus , which is also found in central Brazil, the main distinctions are the hourglass-shaped interorbital region and the anteriorly converging teardrop-shaped incisive foramen of the latter (Costa et al., in press). Geographic limits of these two species are not clear yet, and it is possible that they overlap in central Brazil, but our phylogenetic analyses reveal that these are clearly two distinct species, with an average genetic divergence of 11.3% between them ( Fig. 13 ).

Remarks. R. ipukensis n. sp. can be allocated to the leucodactylus section (sensu Tribe 1996) by its pattern of cariotid circulation and also by its phylogenetically proximity to R. emiliae , which is currently classified within this group.

Measurements (n = 22): HB = 99–141, T = 113–165, HF = 24–28, E = 19–23, W = 35–103. For cranial measurements, see table 3.

Distribution. This species is known from only two localities 300 km apart, in the state of Tocantins: Fazenda Lago Verde (type locality) and Rio Santa Teresa, near Peixe ( Table 1 ). Rhipidomys ipukensis n. sp. is probably endemic to the Araguaia-Tocantins basin in the Cerrado of central Brazil, but more samples are needed to clarify its geographical distribution.

Natural history. Twenty-two individuals were captured in traps placed both on the ground (n = 15) and in the understory (n = 7) in ipucas at FLV, and only two were captured at PEC, one of which was found dead inside a pipetrap (arboreal refuges used for colonization by tree frogs) and only its skull was identified. Twelve adult males had scrotal testes and two adult females were lactating in September 2008.

Etymology. The name derives from the Tupi indigenous term ipuka, meaning água que arrebenta in Portuguese ( Houaiss & Villar 2001), which loosely translates into water spring. Locally, this name is applied to natural forest fragments, which are similar to semi-deciduous alluvial forests of Amazonia, and are located on the Araguaia basin floodplain ( Martins et al. 2002, Martins et al. 2006). Specimens of Rhipidomys ipukensis n. sp. were collected mainly in these ipucas, which are very threatened by the rapid expansion of agriculture in the region.

Vouchers (n = 9: 5ɗ 2Ψ 2 skulls): MN 73741–73744, UFES 1448–1451 (see holotype and paratypes above). We identified an additional specimen of R. ipukensis n. sp. housed in the Mammal Collection at Universidade Federal de Minas Gerais, Belo Horizonte, Brazil (UFMG 2952), collected at Rio Santa Teresa, 20 km NW Peixe, Tocantins, Brazil, 11°50'34"S 48°38'08"W.

Figures

FIGURE 13. Bayesian tree of cyt-b haplotypes from specimens of Rhipidomys, rooted using Thomasomys and Hylaeamys. Bayesian posterior probabilities are in bold and percentages are average Kimura two-parameter distances.

FIGURE 14. Dorsal, ventral and lateral views of skull and mandible of the holotype of Rhipidomys ipukensis n. sp. (male, MN 73741).

FIGURE 15. Detailed views of incisive foramen (left), mesopterigoyd fossa (middle) and subsquamosal foramen (right) of Rhipidomys ipukensis n. sp. (a: MN 73741) and Rhipidomys emiliae (b: DPO 10).

Tables

TABLE 3. External and cranial measurements of vouchers of Rhipidomys ipukensis n. sp. from the state of Tocantins, Brazil, Rhipidomys emiliae from the states of Mato Grosso and Pará, Brazil, and Rhipidomys nitela from Guyana and French Guiana. Mean, standard error (SE) and range are given in millimeters.

HB T HF E W RL	121 ±15.1 140 ±18.9 25.5 ±1.38 21.5 ±1.30 66 ±24.1 9.57 ±0.8	99–141 113–165 24–27 20–23 40–103 8.4–10.55	6 5 6 6 6 7	131 ±12 155 ±10.9 28 ±1.87 20 ±1.29 64.5 ±13.3 9.9 ±0.75	116–156 143–175 26–31 18–22 50–87 8.8–11.29	12 12 12 12 12 14	124.3 ±7.8 147.5 ±9.7 24.5 ±0.6 17.25 ±0.5 9.41 ±0.53	114–133 139–159 24–25 17–18 63 8.45–10.06	4 4 4 4 1 11
NL RB IOB ZB BCB ONL	10.92 ±0.9 6.40 ±0.51 5.45 ±0.34 18.09 ±1.1 12.31 ±0.64 33.7 ±2.51	9.41–12.09 5.62–7.04 4.98–5.89 16.47–19.53 11.36–12.87 29.86–36.22	7 7 7 7 6 6	11.15 ±0.83 6.0 ±0.31 5.37 ±0.30 17.35 ±1.22 12.56 ±0.43 33.5 ±1.8	9.8–12.48 5.68–6.57 4.71–5.83 16.1–19.22 11.65–13.07 31.44–36.86	14 14 14 13 14 14	10.02 ±0.75 5.84 ±0.38 5.23 ±0.44 15.92 ±1.05 12.04 ±0.38 30.86 ±1.37	8.66–11.06 5.34–6.69 4.6–5.57 14.49–17.39 11.59–12.67 28.83–32.92	11 11 11 10 11 11
PL PPL BIT DL TFL PBL	15.61 ±0.79 13.03 ±1.36 2.33 ±0.13 8.99 ±0.74 9.9 ±0.56 5.24 ±0.3	14.28–16.66 11.06–14.47 2.14–2.5 7.94–10.01 8.94–10.51 4.79–5.63	7 6 7 7 7 7	15.44 ±0.95 12.59 ±0.95 2.05 ±0.16 8.64 ±0.57 9.96 ±0.65 4.97 ±0.40	14.43–17.04 11.48–14.43 1.74–2.32 7.9–9.81 8.82–10.82 4.18–5.48	13 13 14 14 14 13	14.16 ±0.73 11.48 ±0.76 1.86 ±0.17 8.06 ±0.42 9.29 ±0.33 4.82 ±0.41	13.06–15.24 10.51–12.81 1.56–2.06 7.37–8.63 8.72–9.66 4.2–5.63	11 11 11 11 9 11
IFL IFB M1B PB1 PB3 MFB	6.68 ±0.45 2.87 ±0.26 1.33 ±0.07 3.57 ±0.3 3.91 ±0.26 2.03 ±0.13	6.11–7.31 2.53–3.14 1.23–1.41 3.15–3.99 3.66–4.4 1.99–2.2	7 7 7 7 7 7	6.83 ±0.48 2.52 ±0.38 1.34 ±0.08 3.27 ±0.19 3.88 ±0.21 2.38 ±0.19	6.1–7.67 1.92–3.2 1.23–1.47 3.07–3.64 3.63–4.29 2.09–2.8	14 13 14 13 13 13	6.25 ±0.41 2.36 ±0.12 1.2 ±0.04 2.89 ±0.24 3.52 ±0.22 2.11 ±0.25	5.7–6.99 2.21–2.53 1.15–1.27 2.61–3.26 3.01–3.78 1.7–2.48	11 11 11 11 11 10
BW BL RH SH MRC ZPL	3.73 ±0.13 4.06 ±0.07 6.55 ±0.59 9.54 ±0.42 4.79 ±0.20 2.96 ±0.33	3.62–3.99 3.99–4.17 5.63–7.35 8.96–10.07 4.55–5.01 2.47–3.51	6 6 7 7 7 7	3.40 ±0.57 3.99 ±0.15 6.43 ±0.46 9.4 ±0.42 4.87 ±0.15 2.71 ±0.22	2.71–4.18 3.68–4.25 5.62–7.31 8.78–10.09 4.50–5.14 2.26–3.02	13 13 14 14 14 14	3.20 ±0.42 3.81 ±0.22 5.9 ±0.3 8.77 ±0.42 4.39 ±0.13 2.31 ±0.09	2.58–3.86 3.36–4.14 5.35–6.3 8.16–9.56 4.16–4.57 2.1–2.38	11 11 11 11 11 11
GLM MMR	17.03 ±1.18 5.04 ±0.19	15.05–18.79 4.8–5.32	7 7	17.29 ±0.97 5.04 ±0.18	16.18–18.78 4.85–5.43	14 14	16.35 ±0.8 4.69 ±0.14	15.45–17.75 4.47–4.92	11 11
DR	3.83 ±0.19	3.48–4.03	7	3.73 ±0.17	3.48–3.92	14	3.41 ±0.13	3.3–3.71	11