Exobiology and Evolutionary Biology

Controls on Paleozoic Rates of Taxonomic Evolution: Ecology, Environment and Preservation

PI: Mark Patzkowsky

Changes in global diversity through time are ultimately driven by variations in taxonomic origination and extinction rates. Because the origin and diversification of major taxonomic groups tends to be concentrated in certain intervals of time, such as those following mass extinctions, knowing how and why taxonomic rates vary can point to important factors leading to the evolution of advanced life. As one example, there is growing evidence to suggest that the dynamics of origination and extinction have undergone secular changes over the course of the Phanerozoic. Extinction rates during the Paleozoic tend to be more diversity-dependent compared to origination rates, whereas in the post-Paleozoic origination and extinction rates tend to be equally diversitydependent. Also, origination cohorts following mass extinctions in the post-Paleozoic tend to be longer lived than other cohorts; this intriguing pattern is not observed in the Paleozoic.
Progress in understanding the relative roles of ecology, environment, and preservation in determining variation in taxonomic rates of evolution during the Phanerozoic is hampered by a lack of detailed comparative studies that apply the same analytical methods to multiple events. Without these uniform comparative studies, statements about similarities and differences in diversity trends and evolutionary rates among biotic events are not based on truly comparable data and methods and are difficult to interpret. We propose to investigate controls on Paleozoic taxonomic rates of origination and extinction in order to search for common patterns and causes. This new proposal will extend previously funded research on the Late Ordovician mass extinction to include two additional Paleozoic mass extinctions: the Late Devonian and the Middle Carboniferous. We will use the same methods developed in our previous work on the Late Ordovician mass extinction and recovery interval so that we can make robust comparisons of diversity patterns and taxonomic rates among all three events. We will use data from the Paleobiology Database for our analyses, which we will supplement with additional data from the literature. Much of our effort will go into vetting the data for taxonomic assignments, stratigraphic resolution, and paleoenvironmental determination. We will perform sample-standardized analyses of diversity and taxonomic rates at both regional and global scales for the Late Devonian and Middle Carboniferous events. Finally, through our comparative approach, we will determine shared patterns and inferred evolutionary processes among these three Paleozoic biotic events as well as identify unique characters of each. Our results will bear on the most important processes that govern diversity and variation in taxonomic rates for the Paleozoic, and more generally, for the Phanerozoic.