897. MIOCENE ISOCRINIDAE (STALKED CRINOIDS) FROM JAPAN AND THEIR BIOGEOGRAPHIC IMPLICATION

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  • 897. 日本産中新世ゴカクウミユリ科とその生物地理的意義
  • 日本産中新世ゴカクウミユリ科とその生物地理的意義〔英文〕
  • ニホンサン チュウシンセイ ゴカクウミユリカ ト ソノ セイブツ チリテキ イ

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Abstract

Three isocrinids, Teliocrinus springeri (Clark), Isocrinus sp. and Isselicrinus sp., are described from the late Early to early Middle Miocene of Japan, and their biogeographic implications are discussed. Teliocrinus had been represented only by a living species distributed in the Indian Ocean, and this discovery not only extends its stratigraphic record back to the Miocene but also widens its geographic distribution to the western Pacific region. Isocrinus sp. is based on many disarticulated columnals and is very similar to Oligocene Isocrinus oregonensis and I. nehalemensis from western Oregon. Isselicrinus sp. is based on fragmentary columnals, representing one of the latest occurrences of this genus. A relatively striking turnover of the isocrinid fauna is presumed to have occurred in the western Pacific during the period between the late Early Miocene and Recent. This turnover includes the disappearance of Teliocrinus, Isocrinus and Isselicrinus from the western Pacific, and the introduction of Metacrinus and Saracrinus into this area. As a possible explanation for this, the northwestward movement of oceanic plates and a collision of a part of Gondwana (Australia/New Guinea) to the Eurasia continent are considered, which probably brought Metacrinus to the western Pacific region and an appearance of a barrier separating the deep-water isocrinid fauna into two provinces. Shallow water dwellers like many species of comasterid comatulids in the Indo-Pacific region are less subjected to such faunal separation.

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