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Growth of the xenomorphic crinoid column (Taxocrinus, Late Mississippian)

Published online by Cambridge University Press:  19 May 2016

Julie I. Wulff
Affiliation:
Department of Geology and Mineralogy, 125 South Oval Mall, The Ohio State University, Columbus 43210
William I. Ausich
Affiliation:
Department of Geology and Mineralogy, 125 South Oval Mall, The Ohio State University, Columbus 43210

Abstract

Two alternative hypotheses for proximal column growth are tested in Taxocrinus cf. T. whitfieldi, a late Mississippian flexible crinoid. The first hypothesis states that new columnals are added at the base of the proximal column (immediately above the generating columnal), whereas the second hypothesis has columnals of the proximal column inserted beneath the aboral cup. In both hypotheses, middle column columnals are inserted beneath the generating columnal and are independent from the proximal column.

External features used to determine points of columnal insertion include wedge-shaped columnals and sharp changes in columnar morphology. Sagittal sections reveal the presence of small columnals, some of which can be interpreted as the last columnals inserted prior to death. Data collected on Taxocrinus cf. T. whitfieldi confirm the first hypothesis. This hypothesis may be applicable to other crinoids with xenomorphic columns.

Type
Research Article
Copyright
Copyright © The Paleontological Society 

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