REVISITING RAUP: EXPLORING THE INFLUENCE OF OUTCROP AREA ON DIVERSITY IN LIGHT OF MODERN SAMPLING TECHNIQUES

Since David Raup's seminal 1976 work, paleontologists have been aware of the relationship between outcrop area and diversity. However, the use of proxies for actual outcrop area, and the lack of lithologic resolution have stymied the establishment of a model in order to assess the importance of outcrop area in shaping our view of past biodiversity. By incorporating lithologic data derived from Alexander Ronov and co-workers into mapped outcrop areas from world-wide geologic maps, we are able to establish a quantitative connection between outcrop area and diversity from the same general environments. A significant power law relation is observed for both marine and terrestrial settings at both global and individual continental scales (p °Ü 0.002; r² between 0.4 and 0.7). The addition of estimated habitat area based on paleogeographic maps does not substantially affect the correlation between outcrop area and diversity; it thus appears that the relation is primarily driven by outcrop area. After noting the correlation between outcrop area and diversity in 1976, Raup pointed out that greater outcrop area can increase diversity in two ways: More area of outcrop allows for greater sampling and thus greater diversity, but it also can allow samples to come from more and different habitats and biogeographic provinces. At that time, it was not possible to differentiate between the two and to evaluate the importance of each. With recent advances in sampling techniques made possible by the Paleobiology Database, it is possible to assess the relative roles of sampling intensity and sampling coverage. After standardizing for sampling intensity, outcrop area continues to explain a substantial, although smaller, portion of global marine diversity (p = 0.015; r² = 0.25). It appears that outcrop area continues to bias our understanding of past biodiversity, despite our advances in sampling methodologies.