Thomas's rice rat

Oryzomys dimidiatus is a medium-sized rice rat, smaller than O. couesi, with thick, lustrous fur and velvety underfur. The hairs on the back are about 6 mm in length. The upperparts are gray-brown with some dark hairs, appearing darker overall than in O. couesi; the color becomes more yellowish towards the sides. According to Thomas, a faint buff line extends from the sides to the inner sides of the hindlegs. The underparts are grayish, contrasting with the buffy underparts of O. couesi. The snout is short and the well-haired ears are partly hidden by the fur. The hands and feet are off-white or brownish above, not white as in O. couesi. The hindfeet show small interdigital webs, but they lack long tufts of hair on the digits and some of the pads are reduced or absent. The tail is about as long as the head and body and contains about 15 rings per centimeter. It is slightly darker (grayish) above than below (whitish), but the difference in color is much less pronounced than in O. couesi. Compared to that of Nectomys, the skull is lightly built and has narrow nasals and a broad, round braincase without conspicuous ridges on it. The zygomatic plate is broad. The incisive foramina (perforations of the front part of the palate) extend between the first molars and are broadest in their back halves. …

Oryzomys dimidiatus is known from three specimens collected in the lowlands of the South Caribbean Coast Autonomous Region in southeastern Nicaragua. The first, an old male, was collected on November 5, 1904, in a banana plantation with very moist red clay on the Río Escondido near El Rama. The second, a young adult male, was caught on July 26, 1966, in dense cane on the south bank of the Río Mico at El Recreo, 15 km (9 mi) west from the location of the first specimen, along with three other rice rats (O. couesi, Melanomys caliginosus, and Oligoryzomys fulvescens), the cotton rat Sigmodon hirsutus, and the cottontail rabbit Sylvilagus brasiliensis. The third was caught at a stream near Bluefields. Reid suggested that the species is semiaquatic, spending some time in the water, like other Oryzomys. The 2019 IUCN Red List assessed the conservation status of Oryzomys dimidiatus as "Data Deficient", noting that very little is currently known about the species.