This study aims to address a central question in paleobiologic research: how variable is evolutionary tempo and mode? Although the issue has been debated for several decades, this study goes beyond earlier approaches in that it is focused on testing whether overall paleoclimatic regime ? the differences between green- and icehouse climates ? and the concomitant rates of environmental change associated with different climate phases play a role in regulating the rate and pattern of evolution. This builds on Sheldon?s (1996) ?plus ça change? model that suggests that the rate of environmental variability influences the evolutionary response. To test this over-arching hypothesis, data will be gathered from a greenhouse (the Late Cretaceous) as well as icehouse intervals (the Neogene). More specifically, we will sample Campanian-Maastrichtian units in the North American Western Interior Seaway (WIS) as well as the Miocene-Pleistocene units of Florida. The analyses will focus on various molluscan lineages that have relatively closely related Cretaceous ancestors and Neogene descendents, such as lucinid, nuculid, and venerid bivalves as well as naticid and turritellid gastropods. The collected specimens will be analyzed using traditional size measurements as well as shape analysis to investigate the nature of morphologic change through the intervals studied. Furthermore, to investigate the effects that stratigraphic architecture may have on the manner in which evolutionary patterns are recorded in the record, we will also examine the same Cretaceous taxonomic groups in the WIS, a foreland basin with relatively continuous sedimentation, with coeval deposits in the US Gulf Coast, a passive-margin setting with substantially more sedimentary breaks.
Broader Significance and Importance: Since Darwin first published his opus that established natural selection as a prominent mechanism for producing evolutionary change, the timing (tempo) and nature (mode) of evolution has remained a persistent theme of numerous studies. The contentiousness of the issue came to the forefront with the advent of ?punctuated equilibrium?, which initiated a range of studies into examining changes in various groups. This study builds on those previous ones, but adds a new dimension to the study of tempo and mode by focusing on whether or not the rate of environmental change can influence the nature of the evolutionary response. Intellectually, the broader significance of this proposal is that this is the first study to specifically examine the influence of different climate modes on the biotas evolutionary response. Furthermore, given the multidisciplinary nature of this study, the PIs will be actively engaged in training undergraduate and graduate students in a broad spectrum of geologic approaches to collecting and analyzing data. Finally, the project involves the synergy between research universities and the Museum of the Earth, which will broaden the venues through which the results and its implications can be disseminated and used as an means of presenting evidence of the scientific evolution debate to the public.
