Assessment of Dwarfing as a Response to Environmental Stress buildup in the end Cretaceous.

Abstract

Planktonic foraminifera has been reported as a model organism for studying Biostratigraphy, Evolutionary biology, Heterochrony and Geochemistry. Certain taxa of Planktic foraminifera have been reported to undergo dwarfing as an ecophenotypic variation under stress environment. Previous studies that have reported dwarfing for Cretaceous- Tertiary intervals used Relative species abundances or basic morphometric analysis for a fixed number of individuals in the population. In this study I identified species that appear to dwarf using Relative species abundance and documented dwarfing in the pre K-T boundary interval using absolute values of morphometric analysis. This analysis was performed for the entire population size for the late Maastrichtian Plummerita hantkeninoides zone CF1 of Bidart, France. An objectively replicable metric system was established and measurements were performed manually using image analysis software. Most of the selected species seem to exhibit a dwarfing trend in the suspected interval: a low Magnetic Susceptibility zone which forms the top ~60 cm in Bidart, France. Results from this study should be replicated on other prominent sections and intervals in order to make further conclusive statements. These preliminary results propose Dwarfing as a proxy to identify stress intervals along with other known ones such as Magnetic Susceptibility and Fragmentation Index.