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Apparent prolonged evolutionary stasis in the middle Eocene hoofed mammal Hyopsodus

Published online by Cambridge University Press:  08 February 2016

Robert M. West*
Affiliation:
Department of Geology, Milwaukee Public Museum, 800 W. Wells Street, Milwaukee, Wisconsin 53233

Abstract

The stratophenetic approach to phylogeny reconstruction, developed in numerous recent papers by Gingerich, has its strongest data base in comprehensive collections from early Eocene rocks in the Big Horn Basin of northwestern Wyoming. Other examples have been criticised for lack of well-documented collection data, making suitable testing of stratophenetic interpretations of evolutionary modes virtually impossible.

Study of Hyopsodus from the middle Eocene Bridger Formation of southwestern Wyoming provides new collection data. Adequate stratigraphic documentation is available, so Gingerich's graphical presentation can be essentially duplicated. In contrast to the complex branching pattern Gingerich interpreted from his data, Bridger Formation Hyopsodus data seems to show little size change through approximately one million years. This stasis or equilibrium condition, which is considered rare by Bookstein et al. (1978), is the only well developed pattern in Bridger Hyopsodus.

Type
Research Article
Copyright
Copyright © The Paleontological Society 

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References

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