Morphological data from coccolith images using Fourier power spectra
A new technique for retrieving morphological data from coccolith images using semi-automatic methods is described. The data are acquired as digital video microscope images, and are analyzed using a Fast Fourier Transform which produces Fourier power spectra reflecting the coccolith morphology. Representative data from these power spectra are used as input to principal component and discriminant function analyses. Scores produced by the discriminant function analysis are plotted to show the intra-generic morphological variation that is identified by the system, and suites of variables that contribute significantly to this separation are determined. The results show that objective, useful morphological information can be retrieved using these techniques. Specimens can be distinguished at both genus and species level, and important variables that contribute to the taxonomic variation in morphology are identified for the first time. Morphological changes affecting all the taxa have been shown to occur during the deposition of the Gault Clay Formation. These changes are especially significant for the Watznaueria genus because this genus was thought to be in evolutionary stasis during the Albian stage. The changes within the genera Watznaueria and Zeugrhabdotus coincide with the junction between the Lower and Upper Gault formations, whilst the genus Prediscosphaera changes during the Upper Gault. The results suggest that evolution takes place in rapid bursts rather than in a gradual manner, and support the hypothesis that punctuated equilibrium is the controlling mode of evolutionary change.