Mining morphological evolution in microfossils using volume density diagrams

A technique is explored to visualize series of bivariate morphometric measurements of microfossil shells through geological time with the help of 3D-animated volume-density distributions. Visualization tests were performed using two existing and published sets of morphometric data, i.e., the Neogene coccolithophorid group Calcidiscus leptoporus-Calcidiscus macintyrei and the planktonic foraminifera plexus of Globorotalia menardii. The technique converts series of downcore bivariate morphometric shell data into a continuous frequency distribution, which can be investigated with the help of a graphical data mining tool called Voxler from Golden Software. This tool allowed us to compose and animate complex subsurface structures raised from morphometric measurements of microfossils, and so provides an intuitive, comprehensive insight into the structure and dynamics of complicated evolutionary patterns. With upcoming future large morphometric data sets for oceanic microfossils, this instructive illustration method may hopefully serve to raise more interest in studying topics like morphological evolution, speciation and advances to achieve more universial species concepts needed so strongly in paleontology. An important conclusion from the experiments is that the structure of size frequency distribution through time shows a stronger differentiation into separate morphotype clusters in the coccolith example than in the case of the investigated planktonic foraminifers. The difference between the groups is explained by the differences in ontogenetic shell growth between the alga C. leptoporus and the foraminifer G. menardii. These differences have implications for morphotype classification and evolutionary research by means of morphometry with coccolithophorids and foraminifers.