Faunal turnover is a pattern of diversification and extinction in taxa throughout the geologic record. Patterns of repeated faunal turnovers are referred to as faunal progression, demonstrated by Decapoda in clawed lobsters and podotrematous and heterotrematous crabs. The transition between podotrematous and heterotrematous crabs is the most recent. Among these, section Raninoida Ahyong, Lai, Sharkey, Colgan & Ng, 2007, commonly called “frog crabs,” constitutes a major monophyletic group with podotrematous body forms, and the focus of our study. Declines in raninoidan diversity were aligned with mass extinction events and major climate shifts, especially cooling. Likewise, diversification within Raninoida occurred in warm, greenhouse climates. Thus, a major factor in patterns of faunal turnover in Decapoda is shown to be environmental conditions. Raninoidan families exhibiting adaptations facilitating back-burrowing preferentially survived the end-Cretaceous mass extinction event, whereas raninoidans lacking such adaptions did not go completely extinct at the end-Cretaceous but failed to recover diversity. Given the diversification of heterotrematous crabs into a wide variety of ecological niches throughout the Cenozoic, competition may be a secondary, but still crucial, factor in this faunal turnover. |
