Trends in Size Selectivity of Gastropod Prey by Naticid Predators: A Case Study from the Stone City Bluff Member




Holman, Victoria

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Predator-prey interactions often provide data on the health and complexity of an ecosystem. Looking back into the past allows us to understand how the trophic web changes over time. Naticids are a family of extant gastropods that prey upon other mollusks and exhibit size selectivity of prey. They create diagnostically shaped drill holes when attacking their prey to reach the soft-bodied organism inside the shell. We have gathered samples from the Whiskey Bridge and Little Brazos localities of the Stone City Bluff Member (Crockett Formation, Claiborne Group, Middle Eocene, central/southeast Texas) to study trends in size selectivity among naticids using drill holes. In this study, we examine the use of naticid drill holes on other gastropods as a proxy for predator size, calculate frequency of predation between the two locales, and determine what statistically significant differences in prey and predator size there are, if any, between the two locales. We used the Wilcox sum-rank test to determine if there are any statistically significant differences between the distribution of sizes of drilled specimens and undrilled specimens. Then, we used a linear correlation model to examine trends between prey size and predator size. There appears to be size selectivity of slightly larger prey present in the Whiskey Bridge locality and in the combined data from both localities. However, this trend is not present as apparently in the Little Brazos locality. Both localities appear to show a statistically significant correlation between drill hole size and drilled gastropod size indicating that larger naticids tend to target larger gastropod prey and smaller naticids tend to target smaller gastropod prey. To verify these findings, more work should be done by others to repeat this study and contextualize other biotic and abiotic factors influencing these observed trends.



Paleontology, Gastropods, Naticids, Paleoecology, Predator-Prey Interactions, Stone City Bluff Member, Drill Holes, Whiskey Bridge, Little Brazos