Degree Year

2004

Document Type

Thesis

Degree Name

Bachelor of Arts

Department

Geology

Advisor(s)

Karla Parsons-Hubbard

Keywords

Biont, Epibiont, Paleoenvironmental

Abstract

Paleocommunities of encrusting organisms exhibit characteristics that allow comparisons of modern and fossil systems and subsequent environmental analyses. Encrusting organisms attach to a substrate that is generally limited in area. Interactions between bionts and the host organism, and bionts and the environment, are preserved on epibiont encrusted fossils. Modern biont communities from known environments can be compared to fossil biont communities in order to determine the ancient environment experienced by that fossil. Using epibionts as a tool in paleo-environmental analyses employs the somewhat problematic idea that the present can be used as a key to the past. I suggest that by using guilds (as opposed to species) of bionts, defined by parameters of lifestyle and habitat, the present can be a key to the past with regard to encrusting communities.

A modern data set from off the coast of Lee Stocking Island, Bahamas, was used in this study. Mytilus edulis shells were experimentally deployed at seven depths from 15m to 275m for a period of two years. After retrieval by the SSETI team, I collected, epibiont data from a total of 52 disarticulated bivalve shells.

To test the method of guild use in paleoenvironmental analysis, I used a fossil data set from the Richmond Group in Indiana, Ordovician in age. I obtained Rafinesquina alternata shells from three shell beds in one rock outcrop and collected epibiont data from a total of 208 of these articulated shells.

I compared epibiont data from the modern and Ordovician data sets using a number of different variables, including: presence of guilds, percent area of shell covered by guilds, relative abundance of guilds, and guild richness. I analyzed results for significant differences in order to determine if the Ordovician data were similar to data from any of the modem environments.

In addition to an analysis of the environment experienced by the Ordovician R. alternata and its encrusting organisms, I will explore several larger concepts. One major question is what parameters will be most useful in the comparison of guilds of encrusting organisms that are separated by a gap of 400 million years. I will also address the viability of using guilds as a tool in making comparisons of once living assemblages across such a large time span. Finally, the underpinning assumption of this research, that the modern can be used as a model for the past, will be discussed.

Included in

Geology Commons

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