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The orientation of strophomenid brachiopods on soft substrates

Published online by Cambridge University Press:  20 May 2016

Roy E. Plotnick ,
Benjamin F. Dattilo ,
Daniel Piquard ,
Jennifer Bauer  and
Joshua Corrie
Roy E. Plotnick
Affiliation:
Department of Earth and Environmental Sciences, University of Illinois at Chicago, 845 W. Taylor St., Chicago, IL 60607, USA,
Benjamin F. Dattilo
Affiliation:
Geosciences Department, Indiana University Purdue University Fort Wayne, 2101 E. Coliseum Blvd, Fort Wayne, IN 46805-1499, USA,
Daniel Piquard
Affiliation:
Department of Earth and Environmental Sciences, University of Illinois at Chicago, 845 W. Taylor St., Chicago, IL 60607, USA,
Jennifer Bauer
Affiliation:
3Department of Geological Sciences, Ohio University, Athens, OH 45701, USA, < jenebauer@gmail.com>
Joshua Corrie
Affiliation:
Department of Biological Sciences, Marshall University, One John Marshall Drive, Huntington, WV 25755, USA,
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Abstract

Strophomenid brachiopods have long been interpreted as “snowshoe” strategists, with their flattened concavo-convex valves providing resistance to foundering in very soft sediments. There has been a sharp difference of opinion in whether the shells were oriented with their convex or their concave surface in contact with the sediment. This study, along with independent evidence from sedimentology, ichnology, and morphology, indicates that the strophomenids lived with their shells concave down (convex up). Experiments indicate the force required to push shells into soft cohesive muds is much greater for the convex up than for the convex down orientation. Forces also increase with shell curvature. All measured forces greatly exceed estimates of the downward force exerted by the weight of the shell, indicating that foundering resistance may not have been the key functional requirement. Instead, a convex up orientation would have provided resistance to overturning in currents, in particular if the valves gaped widely. The “snowshoe” may not be the relevant paradigm for the shell morphology of these forms. An alternative is that they functioned more as a tip-resistant base, similar to those of garden umbrellas or stanchions.

Type
Research Article
Information
Journal of Paleontology , Volume 87 , Issue 5 , September 2013 , pp. 818 - 825
Copyright
Copyright © The Paleontological Society 

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