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Branching geometry and function of multiramous graptoloids

Published online by Cambridge University Press:  08 April 2016

Richard A. Fortey and
Adrian Bell
Richard A. Fortey
Affiliation:
Department of Palaeontology, British Museum (Natural History), Cromwell Road, London SW7 5BD, England
Adrian Bell
Affiliation:
School of Plant Biology, University College of North Wales, Deiniol Road, Bangor, North Wales
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Abstract

We have produced computer simulations of multiramous graptoloids with the intention of defining the rules governing branching strategies and colony form. Close matches between such simulations and real graptolites show that complex rhabdosomes may be produced by the permutation of relatively simple sets of rules. Those designs found in nature produce an efficient and regular distribution of zooids through the area included by an essentially planar rhabdosome. Strikingly geometrical arrays of stipes, such as the Goniograptus and yin/yang patterns, closely approach paradigmatic harvesting arrays. For dichotomously branching anisograptids the evolutionary trend in reduction of “primary stipes” can be explained by the production of larger spreading colonies. Multiramous graptoloids fed during vertical movement through the water column. Changes in a single branching decision may produce considerable changes in rhabdosome morphology, but these are not necessarily of high taxonomic importance; this is proved by a specimen which is a morphological combination of two “genera.” Although primarily under genetic control, certain modifications to colony form were probably the result of inhibitory interaction between adjacent stipes.

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Paleobiology , Volume 13 , Issue 1 , Winter 1987, pp. 1 - 19
Copyright
Copyright © The Paleontological Society 

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References

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