Taxic and phylogenetic approaches to understanding the Late Ordovician mass extinction and Early Silurian recovery.

摘要

The rules governing the accumulation and depletion of diversity vary at different geographic scales. Because of the spatially complex nature of the global ecosystem, understanding major macroevolutionary events requires an understanding of the processes that control diversity and turnover at a variety of geographic and temporal scales. This is of particular importance in the study of mass extinction events, which can eliminate established evolutionary lineages and ecologically dominant taxa, setting the stage for post-extinction radiation of previously obscure or minor lineages. If the macroevolutionary consequences of extinctions and recoveries are to be understood and predicted, the spatial and temporal variations in diversity and turnover must be quantified and the processes underlying these patterns dissected.; Here, I analyze regional diversity and turnover patterns spanning the Late Ordovician mass extinction and Early Silurian recovery using a database of genus occurrences for inarticulate and articulate brachiopods, bivalves, anthozoans and trilobites. Chapter 2 compares sampling standardized diversity and turnover trends for the paleocontinent of Laurentia to the global pattern derived from genus first and last appearances. After accounting for variation in sampling intensity, we find that marine benthic diversity in Laurentia recovered to pre-extinction levels within 5 Myr, which is nearly 15 Myr sooner than suggested by global compilations. The rapid turnover in Laurentia suggests that processes such as immigration may be particularly important in the recovery of regional ecosystems from environmental perturbations.; Chapter 3 explores variability in the dynamics of recovery at the regional scale, by expanding the database both by doubling the number of occurrences for Laurentia and including data from Baltica and Avalonia. These data show that sampling standardized diversity trends for the three regions are variable. Despite the expansion of the database, diversity continues to rebound to pre-extinction levels within 5 Myr of the extinction event in the paleocontinent of Laurentia. However, diversity in Baltica and Avalonia requires 15 Myr or longer to reach pre-extinction levels. This increased rate of recovery in Laurentia is due to both lower Late Ordovician extinction intensities and higher Early Silurian origination rates relative to the other continents. (Abstract shortened by UMI.)