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Oryzomys peninsulae

Oryzomys peninsulae
Skull, seen from above, on a black background, with the number "8" next to it. On the braincase, the number 146618 and the female symbol are written.
Skull of Oryzomys peninsulae, seen from above
"Critically endangered, if not extinct"
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Cricetidae
Genus: Oryzomys
Species: O. peninsulae
Binomial name
Oryzomys peninsulae
Thomas, 1897
Map of western Mexico with a green mark on the southern tip of the Baja California peninsula, an orange mark off the coast of Nayarit, a pink area inland in the southwest, and a red area along the Pacific coast north to Sonora.
Distribution of Oryzomys peninsulae (in dark green) and other western Mexican Oryzomys
Synonyms
  • Oryzomys peninsulæ Thomas, 1897
  • Oryzomys palustris peninsulae: Hershkovitz, 1970
  • Oryzomys couesi peninsularis: Alvarez-Castañeda, 1994
  • Oryzomys couesi peninsulae: Alvarez-Castañeda and Cortés-Calva, 1999

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 was first collected in 1896 and Oldfield Thomas described it in 1897 as a full species of Oryzomys. It was retained as a distinct species related to O. couesi and O. palustris until 1971, when Philip Hershkovitz swept it, and other outlying populations of the same species group, as subspecies under an expanded concept of O. palustris.Raymond Hall concurred in the second edition (1981) of Mammals of North America, arguing that O. peninsulae differed less from mainland Oryzomys populations (currently classified as O. couesi mexicanus) than some other forms he included in O. palustris differed from each other. After studies of the contact zone between North American O. palustris and Central American O. couesi in southern Texas and northeastern Tamaulipas (by Benson and Gehlbach in 1979 and Schmidt and Engstrom in 1994) made clear that the two are distinct from each other, O. peninsulae remained as a subspecies of O. couesi. In 2009, Michael Carleton and Joaquín Arroyo-Cabrales reviewed the classification of western Mexican Oryzomys and used morphological and morphometrical data to characterize four distinct Oryzomys species in the region. O. peninsulae and another isolated population, O. nelsoni from the Islas Marías, were both retained as separate species, as was O. albiventer from montane mainland Mexico. They kept the population in the coastal lowlands as a subspecies, O. couesi mexicanus, of Oryzomys couesi.


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