THE SAMPLING AND ESTIMATION OF MARINE PALEODIVERSITY PATTERNS: IMPLICATIONS OF A PLIOCENE MODEL

Data that accurately capture the spatial structure of biodiversity are required for many paleobiological questions, from assessments of changing provinciality to estimates of global taxonomic or morphological diversity through time, yet the nature of the fossil record makes assembling truly global datasets difficult. Studies of temporal and spatial changes in diversity have attempted to overcome fossil sampling biases through sampling standardization protocols, but such approaches must ultimately be limited by available literature and museum collections. One approach to evaluating such limits is to compare results from the fossil record to models of past diversity patterns informed by modern relationships between diversity and climatic factors. Here, we develop a model for Pliocene diversity patterns by combining present-day patterns for marine bivalves with data on the geologic ages and distributions of extant taxa. We then compare this model to diversity patterns retrieved from the literature as compiled by the Paleobiology Database. The published Pliocene bivalve data lack the first-order spatial structure likely required to generate the modern biogeography within the time available (<3 Myr). Instead, the published data show global diversity maxima in the Tropical West Atlantic and cool-temperate East Atlantic, regardless of the analytical protocol used. Either today’s tropical West Pacific diversity peak, double that of any other tropical region, is a purely Pleistocene phenomenon – highly unlikely given the geologic ages of extant genera and the topology of molecular phylogenies – or the paleontological literature is such a distorted sample of tropical Pliocene diversity that current sampling standardization methods cannot compensate for existing biases. A rigorous understanding of large-scale spatial and temporal diversity patterns will require new approaches that can compensate for such strong bias, presumably by drawing more fully on our understanding of the factors that underlie the deployment of diversity today.