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Intracolony variation in colony morphology in reassembled fossil ramose stenolaemate bryozoans from the Upper Ordovician (Katian) of the Cincinnati Arch region, USA

Published online by Cambridge University Press:  26 July 2016

Marcus M. Key Jr. ,
Patrick N. Wyse Jackson  and
Stephen H. Felton
Marcus M. Key Jr.
Affiliation:
Department of Earth Sciences, Dickinson College, Carlisle, Pennsylvania 17013-2896, USA 〈[email protected]〉
Patrick N. Wyse Jackson
Affiliation:
Department of Geology, Trinity College, Dublin 2, Ireland 〈[email protected]〉
Stephen H. Felton
Affiliation:
DryDredgers.org, 5678 Biscayne Avenue, Cincinnati, Ohio 45248, USA
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Abstract

Clusters of associated colony fragments discovered weathering out of bedding planes in the Upper Ordovician of the Cincinnati, Ohio, region provide a rare opportunity to quantify intracolony variation in ramose stenolaemate bryozoans. Sixteen colonies were reassembled as completely as possible from 198 fragments, and the following colony-level characters were measured: colony dimensions, branch link length and diameter, and branch order. Results indicate that branch link length and diameter systematically decrease as colonies grow via branch bifurcation. Branching ratio (i.e., the number of distal first-order branches divided by the number of immediately proximal second-order branches) appears to be more genetically than environmentally controlled and to be consistent among orders of stenolaemates and perhaps across the phylum. Colonies with endozones mined out by endoskeletozoans result in broken branches as opposed to pristine growing tips. This varies stratigraphically, perhaps in response to the distribution of the boring animals. The rarity of borers and the systematic proximal increase in branch diameter in these colonies suggest the zooids in the proximal portions of the colonies were alive at the time of colony death. If the time and effort can be invested in reassembling colonies, these morphometric data can then be applied to taxonomic, phylogenetic, and paleoenvironmental studies.

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Articles
Information
Journal of Paleontology , Volume 90 , Issue 3 , May 2016 , pp. 400 - 412
Copyright
Copyright © 2016, The Paleontological Society 

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