Analyses of recent data show that Floridian molluscan diversity declined markedly during the Pliocene-Pleistocene mass extinction. This decline in diversity was seen at all trophic levels, indicating a complete collapse of the ecosystem. These findings contradict the notion that there was a species diversity stasis throughout the Pliocene-Pleistocene and that the diversity of Pliocene Florida was equivalent to that of Recent Florida. The mass extinction was a two-staged, sequential event. A similar two-staged mass extinction occurred in the Miocene, indicating that two ecological catastrophes in quick geological succession may have produced this mass extinction as well.