Oligoryzomys pachecoi, Hurtado & D’Elía, 2018

Hurtado, Natalí & D’Elía, Guillermo, 2018, A new species of long-tailed mouse, genus Oligoryzomys Bangs, 1900 (Rodentia: Cricetidae), from the Bolivian Yungas, Zootaxa 4500 (3), pp. 341-362 : 352-353

Oligoryzomys pachecoi n. sp.

Pacheco’s long-tailed mouse

Figures 7 and 8

Holotype: MSB 67304, adult female; collected by Jorge Salazar-Bravo, May 30 1991. Partial cytochrome-b gene sequence (976 pb) of this specimen is available on Genbank with accession number EU192171 ; this sequence is here considered as a hologenetype (sensu Chakrabarty 2008).

Type locality: Bolivia, Cochabamba, Tinkusiri , 17 km E of Totora (17º 45' S, 65º 02' W). This locality is numbered 25 in Fig. 2 .

Paratypes: An adult female ( USNM 271590 ) collected at Bolivia, Department of Chuquisaca, Province of Tomina , 40 km from Tola Orko (19º 27' S, 64º 07' W, locality 22 in Fig. 2 ); and an adult male ( AMNH 264144 ) collected at Bolivia, Department of Tarija, 5 kilometers north northwest of Entre Rios , Oconnor (21º 17' S, 64º 07' W, locality 27 in Fig. 2 )

Geographic distribution: Cloud mountain forests, Yungas, along the eastern slope of the Andes from central to southern Bolivia between 1280 and 1960 m ( Fig. 2 ).

Diagnosis: Medium body size long-tailed mouse (HBL average: 96.09 mm), which differs from its congeners by the following combination of characters: lighter brown dorsal fur without orange appearance; skull with trapezoidal anterior border of nasal bones, wide zygomatic plates, mesopterygoid fossa with anterior border anteriorly always squared, flattened and short bullae with short and wide Eustachian tube, and longer condylar process.

Description: Fur presents moderate dorsal and ventral coloration contrast; dorsally is brown and ventrally is grayish. The orbicular ring is absent. Tail is markedly bicolored. Genal vibrissae surpass the pinna. Carpal vibrissae pass the base of dV. The dV is smaller than dII. Forefeet and hindfeet are dorsally covered with dense, short, and white hairs; do not present carpal or tarsal patches, respectively.

Skull is delicate with a narrow interorbital constriction. Rostrum length is one fourth of skull length. Rostrum breadth at maximum wide of nasals is narrower or subequal than breadth between premaxillary. Anterior borders of nasal bones are trapezoidal. Posterior borders of nasal bones are rounded. Zygomatic notch is deep. Lacrimal bones are squared and small. Zygomatic bridge is narrow Maxillary-frontal-lacrimal joint is generally at the same level of the posterior end of the premaxillary-maxillary-frontal joint. Interorbital region presents straight borders and flat supraorbital margins of the frontal. Zygomatic breadth is slightly broader than the braincase breadth. Posterior border of incisive foramina reaches the anterior border of M1. Zygomatic plate is wide, M1 plus M2 and middle M3 length. Posterolateral palatal pits are posteriorly divergent. Anterior border of mesopterygoid fossa is anteriorly squared. Presphenoid occupies a third of the mesopterygoid fossa. Basisphenoid breadth is narrower than the incisive foramina breadth. Border of palate plate is straight. Auditory bullae are flattened and comparatively small. Eustachian tube is short and wide. Tegmen timpani are in contact with the squamosal. Posterior opening of alisphenoid canal is narrow. Carotid canal is falcate and large. Basioccipital breadth at carotid canal is narrower than breadth between M2. Occipital condyles are rounded. Hamular process is short. Subsquamosal fenestras are short and narrow. Postglenoid foramina are short. Capsular process of the jaw reaches above the sigmoid notch border. Coronoid process is short and wide. Condylar process is longer than the angular. Angular process is broad.

Upper molar rows are parallel. Upper incisors are ungrooved and opistodont, with orange enamel in its anterior surface. Procingulum of the M1 is asymmetrically divided by the anteriomedian flexus. Posteroloph of the M1 reaches the labial surface; posterior border is rounded and broad. Mesoloph of the M1 well developed, and protruded reaching the labial surface. Protoflexus of the M2 is squared. Anteroloph of the M2 reaches the labial surface, is rounded and broad. Mesoloph of the M2 well developed. Anteroloph of the M3 is narrow and reaches labial surface. Mesoloph of the M1 well developed, protruded and clove shaped. Hypocone of M3 is small. Hypoflexids of m1, m2, and m3 are squared. Mesolophids of m1, m2, and m3 well developed. Anterolabial cingulum of the m2 and m3 is broad and rounded (see Fig. S3 ).

Comparisons: Differences with Oligoryzomys brendae , O. destructor , O. f. occidentalis and the form chaparensis are detailed in the qualitative comparisons results.

Measurements of the Holotype in mm: TL=226, BHL=96, T=130, F=23, E=16.5, W= 26g, GLS= 24.79, CIL= 22.42, NL= 9.15, RL= 7.89, RB=4.40, ZB=12.50, BB=11.26, LIB=3.45, LD=6.11, LM=3.64, LBP=4.24, LIF=4.81, BZP=2.73.

Etymology: In honor to Dr. Víctor Raúl Pacheco Torres, a Peruvian mammalogist who has mentoring dozens of students (including the first author of this work) on the systematics and ecology of South American mammals. Likewise, Víctor is the author of a large and important series of papers on distinct issues of Neotropical mammals, including the description of several species of Sigmodontinae (e.g., Pacheco 1991; Pacheco & Patton 1995; Luna & Pacheco 2002; Pacheco et al. 2004, 2014; Rengifo & Pacheco 2015; Jimenez & Pacheco 2016; Uturunco & Pacheco 2016; Hurtado & Pacheco 2017).

Natural History: Anderson (1997) reported (as Oligoryzomys destructor ) three pregnant females in May and April with three, four, and five embryos each, and one lactating female in May. Oligoryzomys pachecoi n. sp. (as Oligoryzomys destructor ) was captured together with other sigmodontines as Akodon fumeus , Oxymycterus paramensis , Neacomys vargasllosai , Oryzomys yunganus , and Rhagomys longilingua in open forests with trees between 30 and 40 m ( Villalpando et al. 2006). Accordingly with Louise Emmons (comm. pers.), in live captures this species has a distinctive odor.

Figures

FIGURE 2. Map showing the collection localities of the specimens of Oligoryzomys brendae (blue) and Oligoryzomys pachecoi n. sp. (pink) revised in this study. Locality numbers correspond to those in the Appendix. Circles indicate localities with specimens only included in the molecular phylogenetic analysis; squares indicate localities with specimens that were only morphologically assessed; triangles indicate that specimens from those localities included in both the phylogenetic and morphological analyses; yellow diamonds indicate type localities. Polygon with black continued line represented the distribution of O. destructor (sensu Hurtado & D’Elía 2018); polygon with black dashed line represent the distribution of O. f. occidentalis (sensu Rivera et al. 2018); and the green polygon represents the Bolivian Yungas (sensu Olson et al. 2001— WWF).

FIGURE 3. Comparisons (from left to right) among Oligoryzomys brendae (MACN 26304), O. destructor (FMNH 24611), O. f. occidentalis (MSB 55318), and Oligoryzomys pachecoi n. sp. (MSB 67304). First row: partial view of the rostrum; second row: partial view of the palatal region and mesopterygoid zone; third row: partial view of the left side of the skull; fourth row: partial view of the jaw. Abbreviations, ab: auditory bullae; ap: angular process; cc: carotid canal; cdp: condylar process; crp: coronoid process; et: Eustachian tube; if: incisive foramina; hp: hamular process; occ: occipital condyle; palc: posterior opening of alisphenoid canal; pgf: postglenoid foramen; ssf: subsquamosal fenestra; zn: zygomatic notch; zp: zygomatic plate.

FIGURE 7. Dorsal, ventral, and lateral views of the skull, and lateral view of the mandible of Oligoryzomys pachecoi n. sp. (Holotype, MSB 67304). Scale bar 10 mm.

FIGURE 8. Dorsal and ventral, views of the skin of Oligoryzomys pachecoi n. sp. (Holotype, MSB 67304). Scale bar 5 cm.