PATTERNS OF ECOLOGICAL DOMINANCE THROUGHOUT THE FOSSIL RECORD: A DEMONSTRATION O F THE PALEOBIOLOGY DATABASE

I will discuss the Paleobiology Database's current coverage and structure and then illustrate its utility by generating a large-scale result from it. The Database now includes five working groups and 74 contributors; over 80 students have been involved. The Database has grown from three to ten major tables that handle references, collections, occurrences, systematics, classification, digital images, and time scales. All software is web based. New scripts allow uploading and viewing images, designing modular display pages for fossil taxa, and drawing customized paleogeographic maps. The Database's strengths include rich information on the contexts of fossil collections, and on relative taxonomic abundance. From the Database's total of more than 32,000 collections, I selected 6372 that included abundances, were geographically and stratigraphically restricted, had complete lists, and excluded microfossils. As a measure of evenness and alpha diversity, I computed dominance as the proportion of specimens belonging to the most abundant species. Dominance is higher in the plant data than in the marine data (vertebrate data were sparse). There are weak differences between lithologies; silts and clays show lower dominance than sands and carbonates. Trends through Phanerozoic time support the suggestion that Sepkoski's famous exponential diversity increase in the Meso-Cenozoic may be a sampling artifact. Dominance does drop (and alpha diversity therefore does increase) from the Ordovician through the Carboniferous. However, Meso-Cenozoic dominance levels vary without a trend and never escape the range seen in the mid-Paleozoic. Indeed, alpha diversity might have been just as impressive in the Carboniferous as it was in the Cretaceous. Much the same patterns are seen when the data are restricted to confirmed marine paleoenvironments, although unusually low dominance in the Tertiary is now more visible. Meanwhile, data for terrestrial environments demonstrate lack of variation among siliciclastic lithologies, plus surprisingly high similarity between the Cretaceous and Tertiary.