Sea-Level Change and the Multiple Causes of Marine Biological Diversity: The Dynamics of Molluscan Origination and Extinction during the Late Cretaceous and Tertiary

Sea-level change is a major influence on benthic faunas on geological time scales and as such a major potential influence on speciation. It is also, however, the cause of hiatuses and disconformities (e.g., sequence boundaries) in the stratigraphic record, which can obscure these influences. To approach this problem, we need some estimate of the completeness or confidence in the observed stratigraphic ranges of the taxa of interest. We have used three methods for both assessing the quality of the preserved stratigraphic record and analyzing it as a source of insights into the role of sea-level change as a cause of speciation. These include: 1) completeness and confidence intervals; 2) comparison between clades; and 3) geographic sources of immigration.

Based on an analysis of first and last appearance data for Cretaceous inoceramid bivalves in the U.S. Western Interior Seaway and Cretaceous-Oligocene turritelline gastropods in the U.S. Gulf and Atlantic Coastal Plains, we conclude that sea-level change is an important influence on speciation, but that it is neither necessary nor sufficient to cause speciation, at least in these groups. A more explicit framework for analyzing the process and causes of speciation points in these cases to different causal factors being most important at different times.