ASSESSING PATTERNS OF MORPHOLOGICAL DIVERSITY IN COCCOLITHOPHORES WHEN COCCOSPHERES ARE EXCLUDED FROM THE FOSSIL RECORD

The fossil record of coccolithophores is predominantly represented by coccoliths, the individual calcitic plates covering a cell’s surface, since coccospheres, the complete articulated test formed from multiple coccoliths, often fall apart in the early stages of fossilization. As a result, the record omits some important biological characters and may bias our understanding and interpretations of this group’s morphological diversity through time. I compare the taxonomic (e.g. which taxa are more morphologically similar) and spatial patterns of morphological diversity based solely on coccolith traits to patterns based solely on coccosphere traits in order to assess the amount of information lost when coccospheres are excluded from the record. I carry out the first series of analyses using first a complete list of taxa, then a taxon list representing just those taxa which readily fossilize (based on species lists from core tops), and a taxon list representing taxa that occasionally enter the record under exceptional preservation (based on Cenozoic Lagerstätten). While both coccosphere and coccolith traits are integral to the same broad biological functions, it is also possible to have an unbalanced representation of those functions, e.g. there might be more coccosphere traits related to sinking behavior. In the second series of analyses, I parse out character sets based on shared biological functions, i.e. sinking behavior of a cell, exchange between a cell and its environment, and [cellular] architecture of test, and asses the level of agreement in both spatial and taxonomic patterns. Preliminary results using 106 extant coccolithophorid species representing all orders and families, indicate that coccosphere-based morphological distances (calculated using Gower dissimilarity) are greater than the corresponding coccolith-based distances, suggesting a more variable nature to coccosphere traits. Nonetheless, both taxonomic patterns and global spatial patterns of morphological disparity based solely on coccolith characters are indistinguishable from patterns based solely on coccosphere characters; both character sets distinguish families from one another and show homogeneous values of disparity across different regions.