The Morphological Diversity of Coccolithophores Across Environments, Geographic Space, and Geologic Time

In this dissertation, I explore how the morphological diversity of coccolithophores, a major group of eukaryotic phytoplankton, manifests at different scales—from the subspecies level as the functional consequences of form, to the biogeographic patterns of disparity of families. The first part of this dissertations evaluates whether the minute morphologies of coccoliths and coccospheres can affect how a cell interacts with its fluid environment. From these biomechanical sinking experiments, I find that the size and shape of coccoliths can slow sinking velocity, and that coccospheres exhibiting asymmetric arrangements of coccoliths will reorient while sinking, demonstrating the relevance of these features. Next, I explore the spatial and environmental structure of morphological diversity in the modern ocean, by quantifying and comparing disparity across biomes and latitudes. Similar to other groups, such as marine invertebrates and flying terrestrial vertebrates, there is no clear gradient to disparity across either latitudes or biomes in this group; in fact, different regions are indistinguishable with respect to morphological disparity. This homogeneity is likely a result of the cosmopolitan range of most extant families. Finally, I examine the potential distortion of morphological disparity in fossil samples which are predominantly made up of disarticulated coccoliths, by analytically degrading extant assemblages. Coccolith morphology is poorly correlated with coccosphere morphology, but makes a reasonable proxy for whole-organism morphology. The disparity of fossil and dead assemblages is indistinguishable from that of the living assemblages, for biome and latitudinal assemblages, and for the families that could be examined. This work serves to buttress and inform future paleontological work on coccolithophorid morphological diversity, as well as to provide insights into the role of different coccolith arrangement and coccosphere shape.