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A unique bivalve–algae life assemblage from the Bear Gulch Limestone (Upper Mississippian) of central Montana

Published online by Cambridge University Press:  19 May 2016

Christopher A. McRoberts  and
George D. Stanley Jr.
Christopher A. McRoberts
Affiliation:
Department of Geology, University of Montana, Missoula 59812
George D. Stanley Jr.
Affiliation:
Department of Geology, University of Montana, Missoula 59812
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Abstract

A single limestone slab is described from the Mississippian Bear Gulch Limestone of central Montana containing more than 100 bivalves, including Caneyella sp. and ?Ptychopteria (Actinopteria) sp., attached in original life positions along an 80-cm-long ?brown alga. The assemblage provides clear evidence of life position and choice of substrate for these pterioids. The bivalves increase in size, and appear to be radially disposed in their attachment sites, along the loosely coiled “kelp-like” alga, indicating little postmortem transport and current activity. The bivalve population is interpreted as living on an algal thallus that was either planktonic or attached to the substrate. Observations and comparisons with modern bivalve—seaweed associations support either view. Evidence for local anoxic conditions and stagnant water help explain the superb preservation and confirm past interpretations of the Bear Gulch Limestone.

Type
Research Article
Information
Journal of Paleontology , Volume 63 , Issue 5 , September 1989 , pp. 578 - 581
Copyright
Copyright © The Paleontological Society 

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