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Shell form in the biconvex articulate Brachiopoda: a geometric analysis

Published online by Cambridge University Press:  08 February 2016

George R. McGhee Jr.
George R. McGhee Jr.*
Affiliation:
Department of Geological Sciences, Wright Geological Laboratory, Rutgers University, New Brunswick, New Jersey 08903
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Abstract

Using a geometric model of shell morphology, it is demonstrated that biconvex brachiopods occupy only a small region of the potential geometric space available to organisms with planispiral exoskeletons composed of two articulated valves. Measurements taken for a sample of 324 genera of the articulate orders Pentamerida, Rhynchonellida, Spiriferida, and Terebratulida were analyzed using a simple geometric model of shell form and ontogeny. The frequency distribution of brachiopod shell morphologies exhibited by the four orders represents the biological optimization of the spatial relationships between area and volume. Biconvex brachiopods develop shells which are designed to minimize shell surface area while maximizing internal shell volume. The means by which optimization is achieved is related directly to the effects of increase in absolute size during ontogeny. The boundaries upon shell geometries utilizable by biconvex brachiopods are determined by (1) limitations of articulation, and (2) limitations of surface and volume.

Type
Articles
Information
Paleobiology , Volume 6 , Issue 1 , Winter 1980 , pp. 57 - 76
Copyright
Copyright © The Paleontological Society 

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