Stepwise growth changes in early post-embryonic stages among Cretaceous tetragonitid ammonoids

In this study, we analyzed the ontogenetic trajectories of shell morphology in some Cretaceous tetragonitid ammonoid specimens (Tetragonitidae) collected from the Tomamae, Mikasa, and Hamanaka areas of Hokkaido, Japan. In all examined species, the ontogenetic trajectories of septal spacing between s...

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Bibliographic Details
Published inPaläontologische Zeitschrift Vol. 97; no. 3; pp. 469 - 483
Main Authors Kawakami, Yoshitaka, Wani, Ryoji
Format Journal Article
LanguageEnglish
Published Berlin/Heidelberg Springer Berlin Heidelberg 01.09.2023
Subjects
Earth and Environmental Science
Earth Sciences
Paleontology
Research Paper
Ontogenetic trajectory
Septal spacing
Tetragonitid
Ammonoid ontogeny
Cretaceous
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Summary:In this study, we analyzed the ontogenetic trajectories of shell morphology in some Cretaceous tetragonitid ammonoid specimens (Tetragonitidae) collected from the Tomamae, Mikasa, and Hamanaka areas of Hokkaido, Japan. In all examined species, the ontogenetic trajectories of septal spacing between successive chambers had similar characteristics during their early ontogeny: two cycles, each comprising an increase and subsequent decrease in septal spacing until ~ 30th septum. The trends of whorl expansion rate changed at 5–7 or ~ 10 mm in the Gaudryceratinae and ~ 3 mm shell diameter in the Tetragonitinae. Based on these observations, we propose that the planktic phases of Gaudryceratinae and Tetragonitinae ended at those shell diameters. These different shell diameters at the end of the planktic phase suggest slightly differing strategies within the family Tetragonitidae.
ISSN:0031-0220
1867-6812
DOI:10.1007/s12542-023-00650-0