Patterns of repopulation following the Cenomanian-Turonian (upper Cretaceous) mass extinction

Mass extinction events punctuate the Phanerozoic history of marine organisms. The high levels of extinction associated with these events played significant roles in determining the history of life. Prompted by attempts to unravel the causes of mass extinction events, several mass extinction boundaries have been studied in great detail. These studies, however, have primarily investigated the fabric and patterns of extinction, but this is only part of an extinction event.;This study focuses on repopulation which can be divided into survival and recovery intervals. For this study, the repopulation following the Cenomanian-Turonian (Late Cretaceous) mass extinction was investigated primarily within the Western Interior Basin of North America. Three sections in northwestern Europe were also analyzed to portray the intercontinental nature of this event.;The repopulation proceeds initially in a series of punctuated increases in diversity and abundance which are bounded by decreases and are at least basinally synchronous. This is followed by a period where diversity increases more gradually and represents the re-establishment of normal faunal structure. The overall structure of the repopulation consists of five phases differentiated based on the types of species present. These phases are characterized by: (1) surviving species; (2) surviving species and Lazarus taxa; (3) Lazarus taxa and new species from Lazarus genera; (4) new species from Lazarus and newly evolved lineages; and (5) new species from newly evolved lineages. The high rate of survivorship across this and other mass extinction boundaries suggests that there must be a wide range of survival mechanisms that species can employ. These include: evolutionary, habitat-related, tropic/life habit-related, reproductive and larval, physiological, and population dynamic survival mechanisms.;The patterns of extinction and repopulation and other sources of evidence, including geochemistry and lithology, point to a number of causes for the Cenomanian-Turonian mass extinction. The probable causes include significant changes in oceanic chemistry and rapid climatic fluctuations which stressed the marine biota. In addition, the differences in repopulation between the Cenomanian-Turonian and Cretaceous-Tertiary mass extinctions suggest that their causes must have been different. This places the 26 My-periodicity hypothesis for mass extinction in question.