Suncus Ehrenberg, 1832

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 : 7-8

Genus Suncus Ehrenberg, 1832

Material examined: A right mandible with I 1, M 1, M 2, and M 3 (MPM-Fo 2802); a left M 2 (MPM-Fo 2803).

Locality: Sabichi Fissure, Ishigaki Island.

Measurements: M 1 (MPM-Fo 2802): L, 2.17 mm; Wa, 1.35 mm; Wp, 1.64 mm. M 2 (MPM-Fo 2802): L, 2.01 mm; Wa, 1.39 mm; Wp, 1.50 mm. M 2 (MPM-Fo 2803): L, 1.97 mm; Wa, 1.32 mm; Wp, 1.60 mm. M 3 (MPM-Fo 2802): L, 1.47 mm; Wa, 0.85 mm.

Description: The mandible, MPM-Fo 2802, is an anterior part without posterior processes, and preserves I 1, M 1, M 2, and M 3. The buccal surface of the mandible is dissolved, exposing incisor and molar roots. The mandibular body is slender but robust dorso-ventrally. The alveolus has root sockets for I 1, lower C, P 4, M 1, M 2, and M 3. The crowns of lower C and P 4 are absent. I 1 has two distinct roots.

Molars show a typical tribosphenic pattern (W-shaped pattern) that is composed of the trigonid and talonid basins. The paraconid is prominent, and is smaller than the protoconid and the metaconid. The main cusps on the molars are connected to each other by sharp crests (e.g., paracristid and protocristid), and surround the isosceles triangle occlusal outline of the trigonid or talonid. The hypoconid connects to the postero-buccal wall of the trigonid by an oblique crest. The postcristid, extending from the hypoconid, joins with a cingulum (or the entocingulid) at the base of the entoconid. The postcristid runs in parallel with the protocristid in occlusal view. The cingulums surround both lingual and buccal bases of the crown. The hypoconulid is absent. Each molar has two roots.

M 2 is same basically as M 1 in terms of occlusal pattern. M 2 is smaller than M 1, but the anterior width of the former is slightly larger than that of the latter. The M 3 talonid is much reduced, and lacks the basal cingulum on the posterior side.

Remarks: Suncus murinus is characterized by lower dental formula, 1.1.1.3, non-reddish tooth, large-size, and much reduced talonid of M 3, and is distinguished from any other species of the Soricidae and Talpidae by these features ( Abe 2000). Suncus murinus is similar in basic dental morphology with two Taiwanese soricids, Soriculus caudatus and Anourosorex squamipes ( Hanamura et al. 1979, 1980). According to them, the dental size of Suncus murinus is intermediate between that of Soriculus caudatus (with smaller teeth) and Anourosorex squamipes (with larger teeth). M 3 of Suncus murinus is more reduced than that of Soriculus caudatus , but larger than that of Anourosorex squamipes . The M 1 cingulum of Anourosorex squamipes extends on the anterior base, whereas that of Suncus murinus surrounds the base from the anterior to the posterior. Suncus murinus from Sabichi Fissure is included in a size variation of extant species ( Suncus murinus riukiuanus from Okinawa Island; Hanamura et al. 1979) and of those collected from Yonaguni Island in this study.

Distribution (natural): South Asia, Southeast Asia, South China, Taiwan, and Ryukyu Islands ( Motokawa 2009).