A New Species of the Heteromorph Ammonoid Didymoceras from the Upper Cretaceous Izumi Group in Shikoku, Southwestern Japan, and Its Evolutionary Implications

DOI 1 Citations 36 References
  • Akihiro Misaki
    Kitakyushu Museum of Natural History and Human History, 2-4-1 Higashida, Yahatahigashi-ku, Kitakyushu, Fukuoka 805-0071, Japan (e-mail: misaki_a@kmnh.jp)
  • Yasuyuki Tsujino
    Tokushima Prefectural Museum, Bunka-no-mori Park, Hachiman-cho, Tokushima 770-8070, Japan

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Description

In this study, a new late Campanian (Late Cretaceous) heteromorph ammonoid, Didymoceras morozumii Misaki and Tsujino sp. nov., from the Hiketa Formation, Izumi Group, southwestern Japan, is described. It is characterized by a loose helical post-embryonic early whorl and relatively tight helical middle whorls, followed by a retroversal hook with a highly elevated apertural end, and two rows of irregular tubercles. Didymoceras morozumii sp. nov. occurs in the upper part of the Didymoceras sp. Zone, which is overlain by the Didymoceras awajiense Zone. Didymoceras awajiense-bearing beds of the Hiketa Formation in the study area is correlated to the lower part of that of the Toyajo Formation in the Kii Peninsula on the basis of the shell forms of D. awajiense. Didymoceras morozumii sp. nov. and D. awajiense have similar characteristics, and it is thought that D. awajiense evolved from D. morozumii sp. nov. As indicated in the descendants, some specimens of D. morozumii sp. nov. are also encrusted by anomiid bivalves.

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Details 詳細情報について

  • CRID
    1360006144034480512
  • NII Article ID
    210000158953
  • DOI
    10.2517/2020pr010
  • ISSN
    13428144
  • Article Type
    journal article
  • Data Source
    • Crossref
    • CiNii Articles
    • KAKEN
    • OpenAIRE

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