COMPARATIVE ANALYSIS OF NATICID PREDATION FROM THE EOCENE-AGE STONE CITY BLUFF MEMBER (SOUTHEAST TEXAS)

Predator-prey interactions often provide data on the environmental health of an ecosystem, and the fossil record of these interactions allows us to understand how trophic webs change over time. Naticids are a family of extant gastropods that prey on other mollusks, including cannibalizing other naticids. Naticids create diagnostic drill holes on prey, the size of which has been demonstrated to correlate to the body size of the predator. Naticids also tend to selectively target prey of specific sizes in response to external environmental pressure. Although the fossil record of naticid drill holes is well-documented in many areas, little research has been done in Eocene formations from southeast Texas. We sampled two localities in Brazos County, Texas (Whiskey Bridge and Little Brazos) of the Stone City Bluff Member (Claiborne Group, Middle Eocene) to study predation patterns among naticids using drill holes. We examined naticid drill hole size as a proxy for predator size and calculated frequency of cannibalistic predation between the two populations. We tested for statistically significant differences between prey (drilled) and non-prey (undrilled) size using the Wilcox sum rank test. We tested for statistically significant linear correlation between predator and prey size. We find a strong size selectivity in the Whiskey Bridge population, as well as a strong linear correlation between prey and predator size. We did not find any statistically significant trends in the Little Brazos locality. These results paired with the higher frequency of predation found in Whiskey Bridge populations, suggest that these populations were experiencing a stronger predation pressure from naticids relative to the Little Brazos locality. This may have been the result of abiotic conditions that allowed naticids to flourish in one locality, but future work is needed to identify exactly which factors contributed to these differences.