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Article: Commensal anomiid bivalves on Late Cretaceous heteromorph ammonites from south-west Japan

Publication: Palaeontology
Volume: 57
Part: 1
Publication Date: January 2014
Page(s): 77 95
Author(s): Akihiro Misaki, Haruyoshi Maeda, Taro Kumagae and Masahiro Ichida
Addition Information

How to Cite

MISAKI, A., MAEDA, H., KUMAGAE, T., ICHIDA, M. 2014. Commensal anomiid bivalves on Late Cretaceous heteromorph ammonites from south-west Japan. Palaeontology57, 1, 77–95, doi: 10.1111/pala.12050

Author Information

  • Akihiro Misaki - Kitakyushu Museum of Natural History and Human History, Yahatahigashi-ku, Kitakyushu, Japan (email:
  • Haruyoshi Maeda - The Kyushu University Museum, Kyushu University, Higashi-ku, Fukuoka, Japan (email:
  • Taro Kumagae - Technical Division, Technical Planning and Coordination Department, Japan Petroleum Exploration Co., Ltd., Chiyoda-ku, Tokyo, Japan (email:
  • Masahiro Ichida - Department of Earth and Planetary Sciences, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto, Japan (email:

Publication History

  • Issue published online: 6 JAN 2014
  • Article first published online: 13 MAY 2013
  • Manuscript Accepted: 7 APR 2013
  • Manuscript Received: 7 DEC 2012

Funded By

Japan Science Society
Japanese Ministry of Education, Culture, Sports, Science and Technology. Grant Number: 24340129

Online Version Hosted By

Wiley Online Library (Free Access)
Get Article: Wiley Online Library [Free Access]


The heteromorph ammonite Pravitoceras sigmoidale from the Upper Cretaceous Seidan Formation (Izumi Group) in south-west Japan is frequently encrusted by sessile anomiid bivalves. Fossils of P. sigmoidale with anomiids are often concentrated at the top of or just above turbidite sandstones. Projecting retroversal hooks and apertures of P. sigmoidale are usually intact, and some individuals are associated with jaw apparatuses near apertures. Anomiids are found on both sides and ventral peripheries of P. sigmoidale conchs, attached predominantly to body chambers. These modes of occurrence suggest that the encrustation by anomiids occurred not on post-mortem floating or sunken carcasses but on live conchs and that these organisms were rapidly buried by turbidity current deposits shortly after death. Attachment to both flanks and ventral peripheries of the retroversal hooks may indicate that at least adult individuals of P. sigmoidale did not lie on the sea floor and did not drag their body chambers. It is suggested that fully mature individuals of this ammonite species lived for a long period of time after having formed the retroversal hook because a few generations of anomiids have colonized a single body chamber. Such colonization by anomiids is also observed on Didymoceras awajiense, which is considered to be the closely related ancestral species of P. sigmoidale. This anomiid-heteromorph ammonite commensal relationship might continue to persist in descendants during the course of evolution of these heteromorph ammonites.

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