Masters Theses

Date of Award

5-1997

Degree Type

Thesis

Degree Name

Master of Science

Major

Geology

Major Professor

Michael L. McKinney

Committee Members

Tom Broadhead, Jim Drake

Abstract

Irregular echinoids are a widespread and diverse group of organisms. Members of modem irregular groups possess varies distributions that reflect biogeographic factors and ecological factors. Recently it has been suggested that species characteristics including body size, local abundances, species richness, and geographic range may exhibit genetic influence over these parameters. These characteristics often determine a taxon's extinction selectivity. The purpose of this project is to examine possible taxonomic influence over these species characteristics by examining an Eocene fossil assemblage and the modem irregular echinoid fauna. The upper Ocala Limestone (Late Eocene) of panhandle Florida contains a well-preserved echinoid fauna. Samples were collected "in situ" and the resultant specimens were identified, counted, and measured. The most species rich group, the clypeasteroids, is also the most abundant. Body size versus abundance plots are constructed that show the classic "hollow curve" pattern with the smallest echinoid, Fibularia vaughni being the most abundant. Further, analysis of 38 fossil species from late Eocene and early Oligocene collections suggests that there is no correlation between large body size and the rarity of a species. The modem irregular fauna is examined by using known geographic distributions. Measurements compiled include geographic range, species richness, and latitudinal occurrence (maximum, absolute minimum, range, northern-, and southern-most). Correlation analysis showed these variables are largely independent. Binomial analysis reveals that geographic range is randomly distributed within genera except for three cases; Echinocardium (unusually localized) and Fibularia and Spatangus (unusually widespread). Chi-square analysis shows that species of species-poor taxa are no more likely to be widespread than species of species-rich taxa. Also discerned from statistical analysis are (1) most irregular echinoid species have relatively small geographic ranges, (2) most genera are species-poor, and (3) irregular echinoids do not follow Rapoport's rule. Geographic range, species richness, species abundance, and body size are often considered in ecological and evolutionary studies. There is no doubt that these characteristics play an important role in the extinction selectivity of a taxon. There is little evidence in this study that genera tend to stack the deck with species that are extinction resistant.

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