Masters Theses

Date of Award

8-1997

Degree Type

Thesis

Degree Name

Master of Science

Major

Geology

Major Professor

Michael L. McKinney

Committee Members

Thomas Broadhead

Abstract

The process and patterns of extinction is a fundamental aspect of evolution and concerns researchers in a multitude of disciplines, from ecology and biology to geology and paleontology. Recent interest has been heightened by the apparent dramatic increase in extinction rates, related, perhaps, to increased anthropogenic activities, which can threaten and destroy habitats of other organisms. While modem ecological study provides detailed insights of interaction between biota, only the rock record contains evidence of evolution on this planet.

Paleontological studies reveal that 95 - 99 % of all species to have ever existed are now extinct. However, extinction is not the sole descriptor of evolution; there is a positive correlation between new originations and extinction. Unfortunately, the fossil record is incomplete and subsequently many biases blur interpretations of evolutionary data. Taphonomic differentials, missing strata, and uncertainty in age-dating all contribute to variations in data sizes and magnify sampling error. Corrections for sample size differences, such as rarefaction, may complicate results further, by inducing mathematical artifacts and assuming random distribution; probability and statistics also assume random response to environmental gradients. This genera to order study of a Cenozoic echinoid database, utilized several approaches to analyze extinction and determine selectivity of some groups over others. Statistical methods yield results biased by sample size, and thus, ultimately by taphonomic constraints. A normalized variance approach was aslo used to reduce sample size artifacts, but it was determined that extinction alone is not sufficient to understand biotic dynamics. The parameters of New Originations (N) and Stable Genera (S) are considered with Extinctions (E) and Genera Present (G), resulting in a new metric, termed Flux:

Flux = G-E+N+S

S+G [(E+1)/(N+1)]

This unit of measure is based upon mass balance, and is the first to consider these four parameters as co-functioning terms. Sample sizes are normalized to reduce sampling error and taphonomic biases are also diminished deriving all four terms from the same dataset. Results of Flux analysis seem to follow wave-form shapes and are consistent with a growing body of evidence indicating periodicity in the fossil record. Additionally, this methodology confirms that high extinction rates are not necessarily bad, since speciation is shown to be so closely linked to extinction. Results of this study show that selectivity is present, mainly as a taphonomic differential. Additionally, the individual trends of each order seem to indicate that response to forcing functions is not random. Variations between flux of similar groups may shed light on phenomena such as competition and predation, with the potential of wave modeling applicable to future study.

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