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Fusellar banding in Silurian retiolitid graptolites

Published online by Cambridge University Press:  20 May 2016

A. C. Lenz
Affiliation:
1Department of Earth Sciences, University of Western Ontario, London, Ontario, Canada N6A 5B7
R. Thorsteinsson
Affiliation:
2Geological Survey of Canada, 3303-33rd Street NW, Calgary, Alberta, Canada T2L 2A7

Abstract

The study of specimens of the retiolitid graptolites Stomatograptus sp., and Agastograptus robustus with a complete or nearly complete periderm permits a better understanding of the growth and development of retiolitids. Incremental layers deposited in more or less concentric layers on skeletal lists are synchronized with the deposition of sheetlike fusellar bands between the lists. Lists, therefore, become progressively more robust, while the periderm of fusellar bands remain single-layered. It appears that before the development of new distal thecal lists and concomitant deposition of fusellar bands can begin, the next proximal-most thecae must be essentially complete. Retiolitid graptolite thecal growth thus appears to mirror that of “normal” graptolites.

Type
Research Article
Copyright
Copyright © The Paleontological Society 

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