Mus Linnaeus, 1758

Nishioka, Yuichiro, Nakagawa, Ryohei, Nunami, Shin & Hirasawa, Satoshi, 2016, Small Mammalian Remains from the Late Holocene Deposits on Ishigaki and Yonaguni Islands, Southwestern Japan, Zoological Studies 55 (5), pp. 1-21 : 18-19

Genus Mus Linnaeus, 1758

Material examined: A left maxilla with M 1 and M 2 (MPM-Fo 2935).

Locality: Indeterminate layer, Umabana-zaki Fissure, Yonaguni Island.

Measurement: See Tables 4 and 5.

Description: The maxilla (MPM-Fo 2935) preserves M 1 and M 2. The teeth are strongly worn. The size is very small, like of a mouse. The posterior end of the incisive foramen reaches as far as the center of M 1 in the occlusal view. There is a small masseteric knob under the zygomatic plate. Enamel structures of the teeth almost disappear due to wearing. The anterostyle on the anterior lamina of M 1 shifts posteriorly, and approaches the enterostyle on the middle lamina. The posterostyle or posterior cingulum is absent on M 1. M 1 has three roots, and M 2 has at least two roots.

Remarks: Mus musculus is a small-sized murid, with three roots on M 1, and this character distinguishes the species from other extant Ryukyu murids all representing distinctly larger-bodied genera, such as Rattus , Tokudaia , and Diplothrix . Apodemus and Micromys are common in mainland Japan (Honshu, Shikoku, and Kyushu), but they are different from MPM-Fo 2935 in having well-developed posterostyle on M 1. Another species of Mus , M. caroli , is known in the Ryukyu area ( Motokawa 2000), but this species usually lacks the masseteric knob that is occurred in living M. musculus and MPM-Fo 2935.

Distribution: Cosmopolitan ( Iwasa 2009a).