Towards a morphological metric of assemblage dynamics in the fossil record: a test case using planktonic foraminifera

With a glance, even the novice naturalist can tell you something about the ecology of a given ecosystem. This is because the morphology of individuals reflects their evolutionary history and ecology, and imparts a distinct ‘look’ to communities—making it possible to immediately discern between deserts and forests, or coral reefs and abyssal plains. Once quantified, morphology can provide a common metric for characterizing communities across space and time and, if measured rapidly, serve as a powerful tool for quantifying biotic dynamics. Here, we present and test a new high-throughput approach for analysing community shape in the fossil record using semi-three-dimensional (3D) morphometrics from vertically stacked images (light microscopic or photogrammetric). We assess the potential informativeness of community morphology in a first analysis of the relationship between 3D morphology, ecology and phylogeny in 16 extant species of planktonic foraminifera—an abundant group in the marine fossil record—and in a preliminary comparison of four assemblages from the North Atlantic. In the species examined, phylogenetic relatedness was most closely correlated with ecology, with all three ecological traits examined (depth habitat, symbiont ecology and biogeography) showing significant phylogenetic signal. By contrast, morphological trees (based on 3D shape similarity) were relatively distantly related to both ecology and phylogeny. Although improvements are needed to realize the full utility of community morphometrics, our approach already provides robust volumetric measurements of assemblage size, a key ecological characteristic.