Zoological Studies

New Records of the Polynesian Rat Rattus exulans (Mammalia: Rodentia) from Taiwan and the Ryukyus

Masaharu Motokawa, Kau-Hung Lu, Masashi Harada and Liang-Kong Lin (2001) The Polynesian rat Rattus exulans (Mammalia: Rodentia: Muridae) is newly recorded from Taiwan and the Ryukyus on the basis of 3 specimens from the lowland area of Kuanghua, Hualien County, eastern Taiwan, and 2 from Miyakojima Island, the southern Ryukyus. This rat may have been introduced by ships sailing to Taiwan and the Ryukyus from other islands where the species occurs. The morphological identification of R. exulans from young R. rattus is established on the basis of cranial measurements. In R. exulans, two measure- ments (breadth across the 1st upper molar and coronal width of the 1st upper molar) are smaller than corre- sponding values in R. rattus.  The alveolar length of the maxillary toothrow is smaller in R. exulans from Taiwan and the Ryukyus than in available conspecific samples from Southeast Asia and other Pacific islands. Thus, this character may be useful in detecting the origin of the northernmost populations of R. exulans represented by the present specimens. The karyotype obtained from one of the Taiwanese specimens does not differ from that previously reported for R. exulans.