Oryzomys balneator Thomas 1900

Oryzomys balneator Thomas 1900, Ann. Mag. Nat. Hist., ser. 7, 5: 273.

Type Locality: Ecuador, Tungurahua Prov., upper Río Pastaza, 20 mi (32 km) E Baños, Mirador, 1500 m.

Vernacular Names: Ecuadoran Oryzomys.

Synonyms: Oryzomys hesperus Anthony 1924.

Distribution: E and S Ecuador, N Perú; range extent uncertain.

Conservation: IUCN – Lower Risk (lc).

Discussion: Not a member of Oryzomys sensu stricto, but relationships obscure. In many features, balneator resembles species of Microryzomys: all are small, soft-furred oryzomyines with a long, scantily-haired tail; delicate cranium with rounded, featureless braincase and small ectotympanic bullae; narrow zygomatic plate with a shallow dorsal notch; complete carotid circulatory pattern (stapedial foramen and squamosal-alisphenoid groove present) and alisphenoid strut absent; brachyodont, pentalophodont molars with bifurcated anterocone, uppers with three roots and lowers two; and conspicuous capsular process on the mandible. Although cognizant of such similarities when composing the Microryzomys revision (Carleton and Musser, 1989), equally numerous differences persuaded us not to include balneator within the genus. The cranium of balneator is larger and differently proportioned than both M. altissimus and M. minutus; its interorbit is much broader and bears a slight post-orbital shelf; the zygoma are convergent anteriorly, not squared; incisive foramina are exceptionally short, terminating well anterior to the M1s; anteroconid is a single cone, not bifurcated as in Microryzomys; the hind feet are comparatively big, more elongate over the metatarsal section, digit V short, and the plantar pad conformation correspondingly shifted. Phylogenetic studies that include representatives of such genera as Microryzomys, Oligoryzomys, and Neacomys should profitably illuminate the relationships of balneator and its generic assignment.