Geographic Variation in Cranial Features of the Polynesian Rat Rattus Exulans (peale, 1848) (mammalia: Rodentia: Muridae)

– Geographic variation in skulls of the Polynesian rat, Rattus exulans (Peale, 1848) (Mammalia: Rodentia: Muridae) was examined based on 18 morphometric characters of 374 specimens collected from the Southeast and East Asia including the continent north of the Isthmus of Kra, the Malay Peninsula, Borneo, Sumatera, Jawa, Philippines, Sulawesi, Flores, Maluku, Taiwan, Ryukyus, New Guinea, and the Pacific Islands. The geographic variations among rats from the Southeast Asian islands were small and samples were similar to each other. The rats from New Guinea were similar to those from the Southeast Asian islands. The rats from the continent and the Malay Peninsula slightly differed from those from the Southeast Asian islands. The rats from the Pacific Islands were different from the rest. The rats from East Asia resembled those from the continent and the Malay Peninsula, but were characterised by the smaller molar size. The origin of the species was suggested to be on the continent north of the Isthmus of Kra. The dispersal may have occurred in association with prehistoric human activity, particularly the populations in New Guinea and the Pacific Islands. No subspecies were recognised regardless of the existence of the geographic differentiation, because R. exulans could be regarded a semi-domesticated animal.