Holochilus sciureus Wagner 1842

PATTON, JAMES L., DA SILVA, MARIA NAZARETH F. & MALCOLM, JAY R., 2000, Mammals Of The Rio Juruá And The Evolutionary And Ecological Diversification Of Amazonia, Bulletin of the American Museum of Natural History 2000 (244), pp. 1-306 : 90-92

Holochilus sciureus Wagner 1842

TYPE LOCALITY: ‘‘Eastern Brazil, Rio San [= São] Francisco,’’ Estado de Minas Gerais (see Hershkovitz, 1955).

DESCRIPTION: This is a moderately largebodied murid rodent with close, soft hair slightly webbed hind feet, and a tail about equal to head and body length. The dorsal color is olivaceous or tawny brown, slightly darker on the midline and becoming paler on the sides. The lateral color grades evenly to that of the venter, with no sharp lateral line or demarcation between dorsal and ventral colors. The ventral color itself is gray washed with orange or buff. The fur is relatively short, rather silky to the touch, and glistening to the eye. The ears are short and round, hairy to the tips inside and out. The tail is never longer than head and body sparsely haired so that the annular scales are readily apparent, and with only a very minimal pencil at the tip. The hind feet are wedge­shaped with a narrow heel but broad plantar surface, with webbing between the toes, and a fringe of down­turned stiff and

silvery hairs along both sides. The sole of the foot lacks prominent granular scales. Females from the Rio Juruá have four pair of mammae, consistent with populations from elsewhere in the states of Amazonas and Goiás in Brazil and Loreto in Perú (see Voss and Carleton, 1993).

The skull (fig. 61) is long and narrow, with strong, diverging zygomatic arches. A narrow, hourglass­shaped interorbital region with a raised edge extends over the temporal region as a distinct ridge. The zygomatic notches are deeply indented, forming an anteriorly projecting spine from the zygomatic plate when viewed from above. The rostrum is relatively short and broad. The palate is narrow and deeply grooved, with a long and oval incisive foramen that nearly extends to the anterior margins of the first molars, and the posterior palatal pits are deep. The parapterygoid fossae are deeply excised and the mesopterygoid fossa extends to the posterior edge of the last molar. A well­developed alisphenoid strut separates the buccinator­masticatory foramen from the foramen ovale acessorius. The otic capsules are globose and moderately inflated. The stapedial foramen is tiny to absent, and both a squamosal­alisphenoid groove and sphenofrontal foramen are lacking. These three characters are indicative of cephalic arterial pattern 3 of Voss (1988; see also Carleton and Musser, 1989). The cheekteeth are moderately high­crowned, with cusps and connecting lophs on a single occlusal plane; the principal cusps are arranged in an alternating pattern. Voss and Carleton (1993) provide a more complete description of H. sciureus and contrast its features with H. brasiliensis . Selected external and cranial measurements of 10 adult specimens of both sexes are given in table 21.

DISTRIBUTION AND HABITAT: As currently understood (Musser and Carleton, 1993), H. sciureus is broadly distributed in the Orinoco and Amazon river basins, through eastern and southern Venezuela, the Guianas, northern and central Brazil, and Amazonian Colombia, Ecuador, Peru´, and Bolivia. Specimens of this species are known only from the middle sections of the Rio Jurua´, up­ and downriver from the town of Eirunepe´. All specimens collected by us were taken in inundated grass patches along the river mar­ Amazonian populations allocated to H. sciureus characterized by a diploid number of 55 to 56.

COMMENTS: Boundaries of extant species within the genus Holochilus are undefined pending a generic­level revision. Massoia (1981) presented evidence for the separation of H. sciureus from H. brasiliensis , a position provisionally followed by Voss and Carleton (1993) and by us here. Other authors (e.g., Reig, 1986; Aguilera and Pérez­ Zapata, 1989; Aguilera et al., 1993) have suggested that H. sciureus itself is composite with Reig noting that amazonicus, guianae and venezuelae are probably valid species As is true for so many South American mammals, the genus Holochilus requires critical revision.

SPECIMENS EXAMINED (n = 6): (i) 1m — MNFS 319; (j) 2f — JLP 15199, MNFS 316 (7) 1m, 1f — JLP 15470, 15479; (9) 1m — JLP 15924. Specimens from Royal Natural History Museum, Stockholm (see Patterson 1992): Rio Eiru´ , Santo Antonio (2m, 1f — 2489, 2490, 2491) ; João Pessoa [= Eirunepe´ (4f — 2376, 2388, 2462, 2476); Igarapé do Gordão (1m, 2f — 2300, 2311, 2408).