WHERE DOES ALL THE DIVERSITY GO AGAIN? A CENOZOIC PERSPECTIVE ON VARIATIONS IN ALPHA, BETA AND GAMMA DIVERSITY IN SHALLOW MARINE ENVIRONMENTS

A focal point in the Phanerozoic trajectory of global biodiversity has been its apparent rapid increase since the end-Cretaceous extinction. The interval stimulates additional interest through the availability of chronologically well-constrained information on changing global paleoenvironments. This knowledge aids understanding of how the Cenozoic diversification of marine invertebrate faunas was influenced by developing global paleogeography, major tectonic shifts, and related climatic transitions.

An extensive dataset (http://paleodb.org) of fossil molluscan occurrences permits analysis of how spatial components of global biodiversity vary through the Cenozoic, specifically how faunas are partitioned biogeographically, how these biogeographic units relate to one another, and their alpha (community-scale) and beta (environmental disparity) diversity characteristics. On a global scale, sampling-standardized diversity appears to have increased at most only 50% over the course of the Eocene-Pleistocene, showing small drops during the Early Oligocene and a slight decline since the Middle Miocene. Nevertheless, there is remarkable stage-to-stage independence in the shape of diversity curves at the regional scale, reflecting both regionally distinct environmental controls and variable data quality, related to reduced sample size. A multivariate analysis of global biogeography reveals that provinciality has increased only slightly during this interval, peaking in the Plio-Pleistocene, although this patterns is strongly influence by spatial sampling intensity. A strengthening latitudinal gradient of diversity is observed through the Neogene, reflecting an increased in not only tropical diversity but also a decline in the richness of faunas from temperate and polar latitudes.

Fluctuations in regional endemism and biogeographic similarity between regions appear related to the opening and closing of major oceanic gateways. Nevertheless some aspects of global and regional diversity patterns reflect Cenozoic-scale climatic transitions, expressed by an Early Oligocene decline. The influence of deteriorating global climate through the Neogene appears to be offset by a steepening latitudinal diversity gradient and an associated increased late Neogene provinciality.