長野県野尻湖層産「ヒメネズミ」切歯化石の分類の再検討

概要

論文の詳細を見る
Of eight forms of mammals recorded from the Nojiri-ko Formation, “Apodemus argenteus”is represented by only one fragmentary lower incisor. Its specific identification is quite questionable, because diagnostic characters of rodent incisors are almost unknown even in recent Japanese species including A. argenteus. Hence the taxonomic position of the incisor is re-examined by detailed observation and measurements, and by comparing with the incisors of four rodent species commonly found in the present Honshu and in the Late Pleistocene fossil localities of the same area (Phaulomys smithii, Microtus montebelli, Apodemus speciosus and A. argenteus). The re-examination reveals that the incisor is clearly distinguished from that of A. argenteus in having much larger dimensions (radius of curvature and mean width) and different characters in cross-section, and is most similar to that of M. montebelli among the four species compared. However, the taxonomic position of the present incisor is indeterminable at family, generic and specific levels, because the morphological characters of the lower incisors are nearly unknown in most living and fossil species of rodents. It can be stressed, at least, that the identification of the incisor as“A. argenteus”is a mistake, and that this specific name should be omitted from the faunal list of the Nojiri-ko Formation.
日本第四紀学会の論文