Abstract
A mammalian dentary discovered in the Coniacian Ashizawa Formation (Fukushima, northeastern Japan) is described. The specimen is a fragment of the horizontal ramus of a left edentulous dentary with five alveoli, the distal four of which are plugged with broken roots. Based on the morphologies of the dentary and the roots, it is considered to be of a therian mammal. This constitutes the first discovery of a Mesozoic mammal in northeastern Japan and highlights the potential for future mammal discoveries in the Cretaceous System in northeastern Japan, which will be significant for disclosure of the mammalian faunal evolution in East Asia during the Late Cretaceous. 論文表題:福島県の上部白亜系足沢層 (双葉層群) から産出した哺乳類の歯骨 抄録 福島県のコニアシアン階足沢層 (双葉層群) より哺乳類の歯骨が発見された.標本は左下顎体の一部で,歯冠は保存されていないものの5つの歯槽があり,そのうち遠心の4つには壊れた歯根が入っている.歯骨や歯根の形態からみて,標本は獣類のものであると考えられる.この標本は東北日本から見つかった初めての中生代哺乳類化石であり,将来的に東北日本の白亜系からさらに哺乳類化石が見つかる可能性を示している.東アジアからは後期白亜紀の哺乳類化石があまり報告されていないので,今後追加標本が得られれば,東アジアにおける後期白亜紀の哺乳類進化を考える上で重要な情報を提供することができるだろう.
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