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Developmental regulation and morphological saltation in the heteromorph ammonite Nipponites

Published online by Cambridge University Press:  08 February 2016

Takashi Okamoto
Takashi Okamoto*
Affiliation:
Geological Institute, University of Tokyo, Hongo 7-3-1, Bunkyo-ku Tokyo 113, Japan
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Abstract

Nipponites, a Late Cretaceous nostoceratid ammonite, shows a peculiar meandering shell growth in the middle-late stage. Assuming neutral buoyancy, and a constant aperture angle relative to the sea bottom, meandering growth of this ammonite was modeled by computer simulation. In this model, the meandering shell growth is controlled by regulation of life orientation. The remarkable similarity in the coiling modes and rib obliquity patterns between the computer-simulated and actual specimens strongly suggests a free living mode of life in Nipponites with an approximately neutral buoyancy. The simulation also suggests that morphological saltation from a simple helicoid form like Eubostrychoceras japonicum to a meandering shell form like Nipponites occurred abruptly without any intermediate form by minor change of the upper and lower limits of growth direction.

Type
Articles
Information
Paleobiology , Volume 14 , Issue 3 , Summer 1988 , pp. 272 - 286
Copyright
Copyright © The Paleontological Society 

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References

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