- journal_title：Journal of Paleontology
- Contributor：Yasufumi Ikeda ; Ryoji Wani
- Publisher：Paleontological Society
- Date：2012-
- Format：text/html
- Language：en
- Identifier：10.1666/11-089R.1
- journal_abbrev：Journal of Paleontology
- issn：0022-3360
- volume：86
- issue：4
- firstpage：605
- section：ARTICLES
d="p-1">The thickness ratios of shell whorls ( = whorl breadth/shell diameter) in the ammonoids d-content genus-species" id="named-content-1">Damesites sugata (Forbes, 1845), d-content genus-species" id="named-content-2">Hypophylloceras subramosum (d="xref-ref-36-1" class="xref-bibr">Shimizu, 1934), and d-content genus-species" id="named-content-3">Gaudryceras tenuiliratum d="xref-ref-56-1" class="xref-bibr">Yabe, 1903 from Late Cretaceous outer shelf deposits in the Kotanbetsu area of northwestern Hokkaido, Japan, were examined in order to determine their mode of migration. The thickness ratios of d-content genus-species" id="named-content-4">D. sugata differ significantly with depth on the outer shelf environment but show no significant difference laterally at a similar depth. These results suggest that d-content genus-species" id="named-content-5">D. sugata did not frequently migrate to different depths on the outer shelf environment but tended to live and migrate laterally at a similar depth on the outer shelf. The thickness ratios of d-content genus-species" id="named-content-6">H. subramosum and d-content genus-species" id="named-content-7">G. tenuiliratum show no significant difference between different depths on the outer shelf environment or for lateral direction at a similar depth. This suggests that d-content genus-species" id="named-content-8">H. subramosum and d-content genus-species" id="named-content-9">G. tenuiliratum frequently migrated at different depths on the outer shelf environment and laterally at a similar depth. There is no difference in hatchling diameters in all the examined species at different depths on the outer shelf environment, suggesting that the thickness ratios became manifest after the post-hatchling stage due to limited migration, which would have been in a nektobenthic habitat. The various modes of migration in the study area are reconstructed in this study, suggesting diversified paleoecology of Late Cretaceous ammonoids.