Date of Award


Document Type


Degree Name

Master of Arts (MA)



First Advisor

P.H. Kelley


Previous studies have shown that naticid gastropod predators are highly selective of prey species in accordance with the Kitchell et al. (1981) cost-benefit model. In addition, earlier studies have demonstrated selectivity of drillhole siting and intraspecific prey size. This study focuses on prey selectivity by Oligocene naticid gastropods and is used to test Vermeij's (1987) hypothesis of escalation. The hypothesis of escalation states that biologic hazards have increased during the Phanerozoic and that organisms have either had to adapt to these hazards or face possible extinction (Vermeij, 1987). Naticid predation on molluscan assemblages is one of several examples used to support the hypothesis of escalation.

Three Oligocene bivalve prey species, Astarte triangulata (547 specimens), Corbula rufaripa (2186 specimens), and Scapharca invidiosa (506 specimens), from three sample intervals within the Red Bluff Formation of Mississippi were used in this study. Data, including prey length, shell thickness, and internal volume, were collected to conduct cost-benefit analyses. In addition, if drilling had occurred on a prey shell, then drillhole site, outer and inner borehole diameter, drillhole type, and drillhole success data were collected. Cost-benefit analyses and analyses of drillhole distributions and intraspecific size selectivity were conducted for these species. The Oligocene results were then compared to those of other fossil assemblages from Tertiary sediments of the United States Coastal Plain.

Interspecific prey selectivity was evident to some degree in the Oligocene at a level similar to that in the Eocene. However, prey selectivity appears less developed than compared to Neogene or Recent assemblages in accordance with the hypothesis of escalation. On the other hand, drillhole site selectivity in the Oligocene was much more prominent than in the Eocene and apparently as well developed as in the Neogene. Prey size selectivity within each species was not developed as much as in the Eocene and Miocene fossil assemblages. These results support the hypothesis of escalation and help define when increases in prey selectivity occurred in the fossil record.

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