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Disparity and constraint in olenelloid trilobites and the Cambrian Radiation

Published online by Cambridge University Press:  08 February 2016

Loren H. Smith  and
Bruce S. Lieberman
Loren H. Smith
Affiliation:
Department of Biology, University of Southern California, 3616 Trousdale Parkway, Los Angeles, California 90089. E-mail: lhsmith@rcf.usc.edu
Bruce S. Lieberman
Affiliation:
Department of Geology, University of Kansas, 120 Lindley Hall, Lawrence, Kansas 66045. E-mail: blieber@eagle.cc.ukans.edu
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Abstract

The Cambrian Radiation marks the appearance of representatives of virtually all major skeletonized phyla in the fossil record and clearly represents a fundamental episode in the history of life. Furthermore, the tempo and mode of this evolutionary event have been the subject of intense debate. One area that has been debated is how so many phylum-level body plans can have evolved in such a geologically brief period. Some have argued that there was enhanced morphological flexibility and fewer evolutionary constraints at this time, leading to greater morphological disparity of Early Cambrian faunas. Others have claimed that this is not true because the evolution of most of the animal phyla significantly predates the radiation or because they failed to detect a signature of decreasing morphological disparity through time. At present, the higher-level patterns of diversification during this time period and the relevant implications for Early Cambrian uniqueness are areas of active research interest and debate. Recognizing this debate, we used both a phylogenetic and a morphometric framework to study whether there is a signature of increasing morphological constraint and decreasing flexibility through time within one of the clades that is a significant constituent of the Early Cambrian biota, specifically, the olenelloid trilobites. In this species-rich clade, we found no evidence that morphological changes were becoming either increasingly constrained or less flexible in one of the dominant Early Cambrian metazoan clades as it passed through the Cambrian Radiation.

Type
Articles
Information
Paleobiology , Volume 25 , Issue 4 , Fall 1999 , pp. 459 - 470
Copyright
Copyright © The Paleontological Society 

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