Lower california rice rat
Oryzomys peninsulae, also known as the Lower California rice rat, is a species of rodent from western Mexico. Restricted to the southern tip of the Baja California peninsula, it is a member of the genus Oryzomys of family Cricetidae. Only about twenty individuals, collected around 1900, are known, and subsequent destruction of its riverine habitat may have driven the species to extinction.
Medium in size for its genus, it was first described as a separate species, but later lumped into other, widespread species until it was reinstated as separate in 2009. It is distinctive in fur color—grayish brown on the forequarters and reddish brown on the hindquarters—and in some dimensions of its skull, with a high braincase, robust zygomatic arches (cheekbones), and long incisive foramina (perforations of the palate between the incisors and the molars).
Oryzomys peninsulae is a medium-sized member of the genus, smaller than O. albiventer but larger than O. couesi mexicanus. Its fur is grayish-brown on the forequarters, but reddish-brown on the hindquarters; this coloration pattern is unique among western Mexican Oryzomys. The underparts are a dirty white, the feet white above, and the tail dark or brownish above and dirty white below.
In the skull, the braincase is high, the zygomatic arches (cheekbones) are broad and squared, and the incisive foramina, which perforate the palate between the incisors and the molars, are long and broad. The upper incisors are orthodont, with their cutting edge nearly vertical. Morphometrically, the skull of O. peninsulae is sharply distinct from other western Mexican Oryzomys.
In fourteen specimens measured by Carleton and Arroyo-Cabrales, total length was 227 to 305 mm (8.9 to 12.0 in), averaging 265.6 mm (10.46 in); head and body length was 113 to 152 mm (4.4 to 6.0 in), averaging 128.9 mm (5.07 in); tail length was 114 to 156 mm (4.5 to 6.1 in), averaging 136.8 mm (5.39 in); hindfoot length was 29 to 34 mm (1.1 to 1.3 in), averaging 32.0 mm (1.26 in); and occipitonasal length (a measure of total skull length) was 27.8 to 34.3 mm (1.09 to 1.35 in), averaging 31.5 mm (1.24 in).
