Fourier analysis of test shape of planktonic foraminifera

Abstract

The exact characterization of test shape is important in morphological studies of foraminifera and other marine micro-fossils Most biometrie studies of microfossils, however, have only measured test diameter or other linear components¹. The tests of planktonic foraminifera exhibit a wide range of morphological traits, some of which are related to environmental conditions and others to the phylogenetic history of the taxon^1,2. Mean test size or linear measurements of chambers and/or whole tests of fossil foraminifera can be used for palaeoecological interpretations from the morphological variations^3–10. We report here that Fourier series analysis could be an objective and unambiguous biometric method for determining the components which comprise the shape of foraminifera. Fourier shape analysis has been successfully applied to fossil ostracods^11,12 , fossil bryozoans^13,14 and miospores¹⁵. In the present study, Fourier series shape analysis was performed on the planktonic foraminifera, Globorotalia truncatulinoides, from the southern Indian Ocean, to differentiate palaeo-environmentally significant trends in the test shape of this species. Kennett¹⁶ and Takayanagi et al.¹⁷ have used linear test measurements to describe latitudinal gradients in the test morphology of G. truncatulinoides. Highly conical forms dominate in tropical waters, whereas more compressed, biconvex forms dominate in cool water.