要　旨　1993年，長鼻類の臼歯化石が千葉県富津市千種新田の海岸において転右として発見された．この臼歯化石は臼歯化石の形態から，ムカシマンモスMammuthus protomammonteus (Matsumoto)と同定された．歯種は咬板数や歯冠幅，歯冠長，歯冠全体の形状などから上顎第4乳臼歯と判別された．本標本は周辺地域の長浜層から洗い出されたものと考えられる．本標本は咬板数が9で，ほぼ完全な標本である．ムカシマンモスの産出は近年千葉県からは報告が少なく，本標本は貴重な追加例となる．さらにムカシマンモスの乳臼歯はこれまで数少なく，はぼ完全な乳臼歯としては，初めての記載例である．ムカシマンモスの臼歯の発生段階あるいは個体発生を知る上で価値のあるものである．

キーワード：ムカシマンモス，Mammuthus protomammonteus，乳臼歯，長浜層

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図版I　千葉県富津市産臼歯化石　Mammuthus protomammonteus (SMNH VeF-63)

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New Material of Mammuthus protomammonteus Molar Tooth from Futtsu-shi, Chiba Prefecture

Hiroyuki Mishima
Department of Anatomy, Nihon University School of Dentistry at Matsudo. Matsudo-shi, Chiba 271-8587
and
Nobuo Mazima
Omiya-chuo High School. Omiya-shi, Saitama 331-0051

Abstract
　　A molar fossil of proboscidea was discovered among boulders on the beach, Chikusashinden district, Futtsu-shi, Chiba prefecture in 1993. The material was identified as Mammuthus protomammonteus (Matsumoto) from its high lamellar frequency, the narrow crown width, and the thin enamel thickness. The molar was judged to be the right maxillary fourth deciduous molar DM4 by the plate number, the length of crown, and the molophogy of molar.
　　The material was considered to be obtained from Nagahama Formation in the middle Pleistocene. The plate number of molar was 9 and it was almost complete specimen. For the first time, the present study described the deciduous molar of Mammuthus protomammonteus (Matsumoto). This deciduous molar fossil is valuable to understand the tooth development and ontogeny of Mammuthus protomammonteus.