Oecomys superans Thomas 1911

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 : 130-131

Oecomys superans Thomas 1911

TYPE LOCALITY: ‘‘Canelos, Rio Bobonaza Orient of Ecuador. Alt. 2100',’’ Provincia de Pastaza, Ecuador.

DESCRIPTION: This is the largest among the five species of Oecomys present in the Rio

Juruá basin (TOL 316 mm; table 29 and fig. 83). It has a long tail, uniformly dark brown in color above and below; tail scales are visible to eye, with 16 scale rows per cm; caudal hairs are short (<2 scale rows in length); and there is no apparent terminal pencil of hairs. The hind feet are distinctly broad and clothed in orangish hair above. The dorsal coloration is dark orangish brown, paling laterally with a weakly developed, but visible orange lateral line; ventral fur color is uniformly gray­based tipped with buff. The dorsal fur is thick and woolly in appearance. Distinct pale orange postauricular patches are present, uniquely so among the species encountered along the Rio Jurua´. The skull (fig. 85) is large (CIL nearly 34 mm) and robust in appearance, with a short, broad rostrum, well­developed, distinctly diverging supraorbital ledges, and moderately shallow zygomatic notches. The upper incisors are more orthodont than in the other species. An alisphenoid strut is present in one, but not the other of the two available specimens; the tegmen tympani is in contact, but does not overlap, with the squamosal; the subsquamosal foramen is small, but open, in both specimens. The incisive foramen is short and slightly oval in shape, not distinctly teardrop in shape as in both O. bicolor and O. roberti ; the maxillary toothrow is long (MTRL, 5.6 mm), more so than in other species in the Juruá basin; the posterior palatal pits are simple, but larger than in all other species; the mesopterygoid fossa is broad with a rounded anterior margin; the parapterygoid fossae are deeply excised; and the bullae are small and uninflated.

SELECTED MEASUREMENTS: See table 29.

DISTRIBUTION AND HABITAT: The capture of only two specimen within the Rio Juruá precludes any conclusions about the true distribution of O. superans within the basin. Both specimens came from right bank localities in the Upper and Lower Central Regions (fig. 81). Both were also taken on the ground in second growth and highly disturbed habitats, such as old garden plots (Altamira, locality 9) and river­edge shrubs (Penedo, locality 7). Our records from the Rio Juruá apparently extend the range of this species eastward from the ‘‘Lower Andean slopes and foothills of E Colombia, Ecuador, and Peru’’ (Musser and Carleton, 1993) into the lowlands of western Amazonia.

REPRODUCTION: The single female was pregnant, with two embryos; the single male was scrotal.

KARYOTYPE: 2n = 80; FN = 108. We have chromosome data for the one specimen from Penedo (locality 7). The karyotype of this individual is identical to that described by Gardner and Patton (1976) for specimens from eastern Perú (Balta, Río Curanja, Departamento de Ucayali) originally allocated to O. concolor , following the nomenclature of Hershkovitz (1960). G. G. Musser (personal commun.), however, has correctly identified these specimens as O. superans . The chromosome complement is also extremely similar to that described above for O. roberti , but with 12 pairs of small metacentric and submetacentric and 24 pairs of acrocentric autosomes, a large submetacentric X­chromosome, and a small acrocentric Y­chromosome.

SPECIMENS EXAMINED (n = 2): (7) 1m — JLP 15517; (9) 1f — MNFS 846.