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土屋健著 ; 田中源吾協力
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Ikeya, Noriyuki ; Tanaka, Gengo ; Tsukagoshi, Akira ; 田中, 源吾
概要:
金沢大学国際基幹教育院GS教育系
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Tanaka, Gengo ; Ikeya, Noriyuki ; 田中, 源吾
概要:
金沢大学国際基幹教育院GS教育系<br />Eighty-five fossil and Recent species of the genus Loxoconcha (Crustacea : Ostracoda) from East As
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ia are systematically reexamined. On the basis of carapace morphology, the genus Loxoconcha from East Asia is divided into five species groups : L. pulchra, L. optima, L. japonica, L. uranouchiensis and L. japonica species groups. The migration and speciation patterns of four species of the L. japonica species group are as follows. In Late Miocene, L. lilljeborgii and L. tumulosa were distributed over the Paleo-Indian Ocean. In Early Pliocene time, these species migrated to the Western Pacific and L. japonica evolved from populations of L. tumulosa by peramorphic evolution. In the Middle Pleistocene, L. shanhaiensis evolved from populations of L. japonica in the Ryukyu Islands by paedomorphic evolution.
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Tanaka, Gengo ; Seto, Koji ; Mukuda, Takao ; Nakano, Yusuke ; 田中, 源吾
概要:
金沢大学国際基幹教育院GS教育系<br />Thirty-five ostracod species belonging to 18 genera are recognized from the Middle Miocene Fujina
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Formation (ca. 14-12 Ma), 3km southwest of Matsue City, Shimane Prefecture, Japan. Most of these species are part of the recent Japan Sea proper water fauna; they are also classified into 4 categories, circumpolar, cryophilic, endemic cool-temperate and temperate species. These ostracod assemblages indicate that the Fujina Formation was deposited under a cold-water environment. Ten new species, Ambtonia shimanensis, A. takayasui, Acanthocythereis fujinaensis, A. izumoensis, Cluthia tamayuensis, C. subjaponica, Kotoracythere tsukagoshii, Laperousecythere ikeyai, Palmoconcha irizukii, and Robertsonites yatsukanus are described.
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小松 , 俊文 ; 前川, 匠 ; 重田, 康成 ; 高橋, 修 ; 田中, 源吾 ; Dang T., Huyen ; Komatsu, Toshifumi ; Maekawa, Takumi ; Shigeta, Yasunari ; Tanaka, Gengo
概要:
金沢大学国際基幹教育院GS教育系
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田中, 源吾 ; Tanaka, Gengo
概要:
金沢大学国際基幹教育院GS教育系
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田中, 源吾 ; Suzuki, Yutaro ; Tanaka, Gengo
概要:
金沢大学国際基幹教育院GS教育系
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田中, 源吾 ; Tanaka, Gengo
概要:
金沢大学国際基幹教育院GS教育系<br />The Light-Switch Hypothesis' proposed by Parker (2003) is reviewed on the basis of recent relevant
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literature in order to test the hypothesis. This review revealed the following: 1) Diversification of bilaterian animals occurred during the Late Ediacaran Period, based on paleontological and molecular clock evidences. 2) Developmental genetic studies of eyes suggest that the eyes of bilaterian animals were formed from those of the Urbilateria, which hypothetically had both rhabdom and cilium photoreceptors during the Ediacaran period. During evolution, vertebrates utilized cilium photoreceptors, while invertebrates selected rhabdom photoreceptors for the development of eyes. On the basis of the detailed research of the ommatidium surface of the low-light adapted compound eye of the fruit fly, the phenotype of corneal nipple protuberances has changed in a extremely short time period from the view point of the geologic time scale. 3) The oldest fossilized eyes discovered are those of trilobite and bradoriid arthropods from 521 Ma. Increases in body size, and the corresponding increase of energy required, during 630Ma-521Ma may have been triggered by the evolution of the eye.
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前田, 晴良 ; 上田, 直人 ; 西村, 智弘 ; 田中, 源吾 ; 野村, 真一 ; 松岡, 廣繁 ; Maeda, Haruyoshi ; Ueda, Naoto ; Nishimura, Tomohiro ; Tanaka, Gengo ; Nomura, Shin'ichi ; Matsuoka, Hiroshige
概要:
金沢大学国際基幹教育院GS教育系<br />高知県佐川地域に分布する七良谷層の模式層序周辺の泥質砂岩中から，最上部ジュラ系を示す2種類のアンモノイド化石を発見した．そのうちAspidoceras属は，テチス海地域の最上部ジュラ系から多産し，
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Hybonoticeras属は同地域のキンメリッジアン−チトニアン階境界付近を示準するタクサである．これらの化石の産出により，七良谷層は最上部ジュラ系（キンメリッジアン−チトニアン階）に対比される可能性が高い．この結論は放散虫化石層序とおおむね調和的である．これまで七良谷層は，上部ジュラ系−下部白亜系鳥巣層群の層序的下位にあたる地層と考えられてきた．しかし七良谷層から産出したアンモノイドの示す時代は，鳥巣層群産アンモノイドのレンジと明らかに重複し，アンモノイド化石からは両岩相層序ユニットの時代差は識別できない．したがって，今後，七良谷層と鳥巣層群の層序関係を再検討する必要がある．<br />The Naradani Formation is located to the south of the Torinosu Group in the Sakawa district of Kochi, southwest Japan, and consists of a linear, narrowly distributed series of marine clastic deposits that contain allochthonous limestone blocks. This formation was previously correlated to the Bajocian–Bathonian Middle Jurassic using brachiopods extracted from the limestone blocks, with later radiolarian correlations suggesting an Oxfordian–Kimmeridgian Upper Jurassic age. The formation has also been interpreted to underlie the Upper Jurassic–Lower Cretaceous Torinosu Group. However, the discovery of two stage-diagnostic aspidoceratid ammonoids, Aspidoceras sp. and Hybonoticeras sp., from muddy sandstones in the stratotype area of the Naradani Formation casts doubt on these previous interpretations. Aspidoceras was widespread during the latest Jurassic, and the presence of Hybonoticeras limits this short stratigraphic interval to the Kimmeridgian–Tithonian boundary in various Tethyan sections. This clearly suggests a latest Jurassic age for the Naradani Formation and generally supports the radiolarian biostratigraphy age-assignment. However, the ranges of ammonoids from the Naradani Formation overlap those from the Torinosu Group, meaning that it is not possible to determine an age-difference between these two lithostratigraphic units. Further research is needed to test other hypotheses, for example to determine whether heterotopic facies relationships exist between the Naradani Formation and the Torinosu Group.
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田中, 源吾 ; 伊丹, 美穂 ; 黒澤, 幸愛 ; 吉岡, あゆみ ; 横田, 麻莉 ; 新井, 理菜 ; 出原, 祐樹 ; 林, 広樹 ; Tanaka, Gengo ; Itami, Miho ; Kurosawa, Sachie ; Yoshioka, Ayumi ; Yokota, Mari ; Arai, Rna ; Idehara, Yuki ; Hayashi, Hiroki
概要:
金沢大学国際基幹教育院GS教育系<br />群馬県富岡市南西部の大島付近の鏑川沿いに分布する中部中新統富岡層群小幡層において‘古蛇崩い礁’と呼ばれる隣接地域とは岩相が著しく異なった地層が露出している．今回，微化石群集を用いて，当該地層の堆積
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年代と堆積環境の再検討を行った．介形虫化石および岩相解析の結果，‘古蛇崩い礁’は，漸深海の石英斑岩の海底面上に浅海からの堆積物重力流による流れ込みで形成された堆積物であることが明らかとなった．また有孔虫と介形虫化石から，当該地層は前期中新世後期〜中期中新世前期のいわゆる「中新世熱帯海中気候事件」期に堆積したものであることが判明した．本邦における「中新世熱帯海中気候事件」期の漸深海性介形虫化石群としては2例目の報告となる．<br />We present a micropaleontological re-examination of the depositional environment of the ‘Kojyakui-sho’ sediments of the Middle Miocene Obata Formation, part of the Tomioka Group, located along the Kabura-gawa River near Tajima, Tomioka City, western Gunma Prefecture, central Japan. These sediments contain sublittoral and bathyal ostracods, and were deposited in the bathyal zone on a quartz-porphyry bedrock seafloor during the late Early to early Middle Miocene. Planktonic foraminifera and ostracods within these samples indicate that the ‘Kojyakui-sho’ sediments formed during the Miocene Climatic Optimum; this is the second reported occurrence of these Miocene Climatic Optimum bathyal ostracod species in Japan.
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