Testing the fossil record: Sampling proxies and scaling in the British Triassic-Jurassic

The quality of the fossil record varies immensely across taxa, geographic regions, environments and time intervals. Because much of this variation can be confounded when examining global patterns, we present a detailed investigation of the British Triassic and Jurassic, one of the most intensively studied pairs of systems in the world. Marine Jurassic palaeodiversity is at least partly controlled by rock availability and accessibility. The terrestrial record is patchier, and effects of rock availability are overprinted by a stronger signal of sporadic preservation. These results also fit a sea-level driven common-cause explanation, as one would expect to see close correlation between rock availability and palaeodiversity in the marine realm, but less so in the terrestrial. Formation counts and palaeodiversity do not correlate, a surprising result given the number of earlier studies that have found close correlations. However, this study differs from most others in that formation counts and palaeodiversity metrics are derived from independent data sources, and so within-study redundancy is avoided. The study confirms the complexity of rock-fossil time series, and the likelihood that the fossil record documents a complex mix of potential biological signal, common cause signal, and rock record and sampling bias. It may be impossible to identify a useful simple sampling proxy for the fossil record that captures every bias and sampling error. Ironically, when preservation is good, sampling proxies representing rock availability, such as outcrop area, can be used to predict palaeodiversity, but are ineffectual when the fossil record is patchy.