The effects of mass extinction on escalation of the naticid gastropod predator-prey system at the Eocene-Oligocene

In 1987, Vermeij proposed the hypothesis of escalation, which states that biological hazards, such as predation, have increased through the Phanerozoic. This hypothesis has been extremely controversial due to the fact that it assumes that biotic factors, such as predation, have had an important role in evolution. Several studies have focused on the validity of the hypothesis of escalation. Kelley and Hansen (1996) offered a modified exposition of the escalation hypothesis. The Kelley-Hansen hypothesis states that escalation cycles are punctuated by periods of mass extinction. The periods of mass extinction would preferentially eliminate the highly escalated prey and, therefore, a new cycle would be initiated. In this study the Kelley-Hansen hypothesis was tested at the Eocene Oligocene extinction boundary in central Mississippi. The levels of escalation of specimens from the Moodys Branch Formation, which lies below the extinction boundary, and the Red Bluff Formation, which lies above the extinction boundary, were compared. The comparison was conducted with several statistical analyses including chi-squared tests and Mann-Whitney U tests. These tests indicated that the Red Bluff Formation did not exhibit higher levels of escalation. In fact, they indicated that the fauna of the Moodys Branch Formation was more highly escalated. These results from the Eocene Oligocene did not support the Kelley-Hansen hypothesis. However, previous studies from the Cretaceous-Tertiary boundary found support for this hypothesis. On the basis of these different results, it can be concluded that the extinctions at the Eocene-Oligocene and the Cretaceous-Tertiary boundaries had fundamentally different effects on the mollusk faunas