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Heterochrony and the achievement of the multibrachiate grade in camerate crinoids

Published online by Cambridge University Press:  08 April 2016

Thomas W. Broadhead
Thomas W. Broadhead*
Affiliation:
Department of Geological Sciences, University of Tennessee, Knoxville, Tennessee 37996
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Abstract

The multibrachiate grade of organization in camerate crinoids was principally attained through pinnule differentiation: the accelerated development of a proximal pinnule that ultimately became a pinnule-bearing arm. Although pinnule differentiation is not the only means of achieving a multibrachiate organization in modern crinoids, it was the primary mode in producing both dichotomous and exotomous branching patterns in multibrachiate camerates. Whereas most of the proximal branchings, commonly fixed in the cup of camerates, were due to pinnule differentiaton, the first dichotomy and distal dichotomies above the cup apparently developed from direct modification of a brachial plate at the growing tip of the immature crinoid arm.

Type
Articles
Information
Paleobiology , Volume 13 , Issue 2 , Spring 1987 , pp. 177 - 186
Copyright
Copyright © The Paleontological Society 

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References

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