Large–scale heterogeneity of the fossil record: implications for Phanerozoic biodiversity studies

Abstract

Patterns of origination, extinction and standing diversity through time have been inferred from tallies of taxa preserved in the fossil record. This approach assumes that sampling of the fossil record is effectively uniform over time. Although recent evidence suggests that our sampling of the available rock record has indeed been very thorough and effective, there is also overwhelming evidence that the rock record available for sampling is itself distorted by major systematic biases. Data on rock outcrop area compiled for post-Palaeozoic sediments from Western Europe at stage level are presented. These show a strongly cyclical pattern corresponding to first- and second-order sequence stratigraphical depositional cycles. Standing diversity increases over time and, at the coarsest scale, is decoupled from surface outcrop area. This increasing trend can therefore be considered a real pattern. Changes in standing diversity and origination rates over time-scales measured in tens of millions of years, however, are strongly correlated with surface outcrop area. Extinction peaks conform to a random-walk model, but larger peaks occur at just two positions with respect to second-order stratigraphical sequences, towards the culmination of stacked transgressive system tracts and close to system bases, precisely the positions where taxonomic last occurrences are predicted to cluster under a random distribution model. Many of the taxonomic patterns that have been described from the fossil record conform to a species-area effect. Whether this arises primarily from sampling bias, or from changing surface area of marine shelf seas through time and its effect on biodiversity, remains problematic.

The fossil record and macroevolutionary history of the beetles

“…The intervening middle through to the Late Cretaceous is a period of particularly low sampling, both in terms of number of collections and number of occurrences (figure 1). A similar pattern has been documented in the fossil record of continental vertebrates [26,27] and there is still debate as to whether this is attributable to larger global processes, such as marine transgressive and regressive cycles [28,29]. Our occurrence database permits an additional quantitative description of the variation in sampling over time, obtained as the proportion of families that range through an interval (i.e.…”

Recovery from the most profound mass extinction of all time

“…This is especially true in the fossil record where patterns of global diversity often reflect patterns of fossiliferous rock availability (Raup 1972;Peters & Foote 2001;Smith 2001;Smith & McGowan 2005). In this study, we use an alternative approach by sampling individual fossil communities (Alroy et al 2001).…”

The origins of modern biodiversity on land

“…Studies of marine data sets show close correlation of diversity and map area, interpreted as evidence of a rock volume control on apparent diversity (e.g. Smith 2001Smith , 2007Smith & McGowan 2008), although a study of global map areas of terrestrial sediments found no such control on terrestrial diversity data (Kalmar & Currie 2010).…”

“…For example, Padian & Clemens (1985), Behrensmeyer et al (2000) and Smith (2001) note that the terrestrial fossil record is poorer than the marine because sedimentation is typically more sporadic, many organisms live in habitats such as deserts, forests and mountains where deposition is limited, and terrestrial rocks are harder to date than marine. These are valid points, and yet the important question is not whether the terrestrial fossil record is perfect, or even good, but whether it is adequate for the studies in hand.…”