A SIMULATION-BASED APPROACH FOR INVESTIGATING THE INFLUENCE OF EPI-CONTINENTAL SEAWAYS ON PHANEROZOIC MARINE BIODIVERSITY ESTIMATES

Much of the fossil record of marine invertebrate diversity is sampled from epi-continental seaways. Such seaways were typically vast (106 km2) and shallow (10s-100s m deep). This contrasts with the modern marine realm, where epi-continental seas are fewer in number and typically an order of magnitude smaller. This difference may have a two-fold impact on our understanding of marine diversity patterns through time. 1. Evolutionary processes may be different within large epi-continetal seaways, giving rise to genuine differences in evolutionary pattern and process when such seaways constitute a major fraction of the total marine environment. 2. Sampling biases may be different between environments within epi-continental seas and those elsewhere. Thus as the proportions of open shelf and epi-continental sea deposits have changed through time, so to might the biases that have effected such proxies of diversity as number of ecosystems sampled, outcrop area, number of named formations, or number of specimens collected.

To investigate the possible influence of epi-contiental seaways on marine biodiversity a simple model of three connected areas was developed from the SPARTA model (Upchurch and McGowan). Simulated fossil records for epi-continental versus ‘open-shelf' areas were generated using standard birth-death models. Taxon dispersal ability, and area carrying-capacities were also included in the model. Sea-level was adjusted to link and isolate the three areas.

The behaviour of the model was investigated through sensitivity analysis. This allowed the generation of simulated datasets to determine how large the differences in evolutionary rates would have to be for them to be distinguishable among different areas. SPARTA allows for data-degradation and this facilitates study of the effect of the destruction of fossil record. This is important in understanding the effects of the incompleteness of the fossil record on our ability to identify genuine differences in evolutionary rates among environments.

Data from the Paleobiology Database Project (http://www.pbdb.org) was used to test for whether differences were detectable in evolutionary rates between areas with high versus low fractions of epi-continental seas throughout the Phanerozoic.