Revisiting Raup: exploring the influence of outcrop area on diversity in light of modern sample-standardization techniques

Abstract

Since David Raup's seminal 1976 work, paleontologists have been aware of the relationship between outcrop area and diversity. By incorporating lithologic data derived from Alexander Ronov and coworkers into our own data on areas of mapped outcrops from worldwide geologic maps, we are able to establish a quantitative connection between area of sedimentary rock exposure and diversity from the same general depositional environments. Significant power-law relations are observed at both global and continental scales of consideration. The addition of data on areas of habitable area estimated from paleogeographic maps does not substantially affect these correlations between outcrop area and diversity, indicating that the relation between outcrop area and diversity is primarily a function of sampling and not a common cause such as sea level. We observe a significant diversity-area effect, first noted by Jack Sepkoski in the marine realm. Unlike Sepkoski's, however, our diversity-area effect appears to play a substantial role in influencing diversity through time; a true global diversity signal appears to be contained in the rock record despite the impacts of variable sampling.Greater outcrop area can serve to increase estimated diversity by increasing both the sample size and the range of habitats and biogeographic provinces sampled. After standardizing for pure sampling intensity by rarefying the number of taxon occurrences, outcrop area continues to explain a substantial portion of global marine diversity. This indicates that coverage, or sampling from multiple habitats and biogeographic provinces, is even more important than sampling intensity. If we remove the effect of outcrop area from our estimate of global biodiversity, we do not observe a net increase in diversity toward the present, lending support to other studies that have not supported a substantial, long-term global increase in biodiversity during the Phanerozoic.

Exceptionally Preserved Fossil Assemblages Through Geologic Time and Space

“…As a direct consequence of such phenomena, the availability of non-marine rock improves toward the present ( Fig. 10; Wall et al, 2009), and more non-marine assemblages have been sampled from younger than older geologic intervals. Whereas older deposits were destroyed, younger ones have more readily survived to the present.…”

The ties linking rock and fossil records and why they are important for palaeobiodiversity studies

“…These include studies that estimate the surface outcrop area of terrestrial or marine sedimentary rocks from geological maps and their accompanying memoirs (Ramp 1976;Smith 2001;Crampton et al 2003;Smith & McGowan 2007;McGowan & Smith 2008;Barrett et al 2009;Wall et al 2009Wall et al , 2011 or counts of the numbers of named formations (Peters & Foote 2001;Crampton et al 2003;Benson et al 2009;Mannion et al 2010;. In all cases a statistically significant positive correlation has been demonstrated linking the rock and fossil records, both in marine and terrestrial environments.…”

“…Most commonly regional rock record compilations have been tested against global diversity estimates (Smith 2001;Peters & Foote 2001;Smith & McGowan 2007;McGowan & Smith 2008;Benson et al 2009). Global rock record outcrop estimates are available (Ronov 1978) but are compiled at a much coarser time-scale compared to diversity estimates (see Wall et al 2009). However, not all studies suffer from this problem.…”

“…Uhen & Pyenson 2007;Wall et al 2009). Dunhill (2011) has shown that, for a series of 50 sites within England and Wales, the area of rock outcropping and the amount of rock exposure (i.e.…”

A simulation-based examination of residual diversity estimates as a method of correcting for sampling bias

“…The residual diversity method has proven popular, particularly in analyses of terrestrial vertebrate datasets where sample sizes are sometimes too small for subsampling (Smith and McGowan, 2008;Barrett et al, 2009;Butler et al, 2009Butler et al, , 2011Wall et al, 2009;Benson et al, 2010;Brocklehurst et al, 2012Brocklehurst et al, , 2013Benson and Upchurch, 2013;Fröbisch, 2013Fröbisch, , 2014Pearson et al, 2013). Lloyd (2012) refined the method, allowing for non-linear relationships between the sampling proxy and diversity, and also introducing confidence intervals to show which peaks and troughs are significant.…”