Title page for ETD etd-07152010-020200

Type of Document Master's Thesis
Author McKeever, Lauren Joann
URN etd-07152010-020200
Title Geographical variation in the genus Astarte (Phylum Mollusca: Class Bivalvia) from the Yorktown and Jackson Bluff formations (early Pliocene) of the Atlantic coastal plain
Degree Master of Science
Department Geological Sciences
Advisory Committee
Advisor Name Title
Gilinsky, Norman L. Committee Chair
Bambach, Richard K. Committee Member
Carter, Joseph G. Committee Member
  • Bivalves
Date of Defense 1985-06-15
Availability restricted
Geographical variation in taxa must be considered in evolutionary

studies. The purpose of the present study is to demonstrate how geographical variation can be measured and documented for a taxon for one slice of time. Future evolutionary studies should document geographical variation for the entire geographical range of the species involved at several points of time throughout its total stratigraphic range. Thus the variation that is present at one time horizon may be separated from the variation that occurs through time.

This work consists of a study of geographical variation in the genus Astarte (Phylum Mollusca: Class Bivalvia) from the Yorktown and Jackson Bluff Formations (early Pliocene) of the Atlantic Coastal Plain. Factor analysis, multivariate analysis of variance, and discriminant analysis were performed on measurements of specimens of Astarte from ten localities. There are significant differences in the morphologies of individuals among localities. These differences are due to the presence of different species of Astarte and to variation in size and external ornamentation within the same species. Seven species recognized from literature on Pliocene Astarte were identified among the individuals of the ten localities, but the statistical results indicate that these seven

species may be grouped into three "types" that mayor may not represent species. The three types occur together in some localities, suggesting that they are distinct species living in sympatry. Factors influencing geographical variation include larval dispersal strategy and the effect of the environment.

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