THE ROLE OF PRESERVATION ON THE QUANTIFICATION OF MORPHOLOGY AND PATTERNS OF DISPARITY WITHIN PALEOZOIC ECHINODERMS

The loss or alteration of morphology as a result of taphonomic processes is the largest potential bias in the study of morphological diversity. This issue is likely and problematically non-uniform through time, stratigraphic sequences, or between depositional facies. In addition, the problem is likely exaggerated at higher taxonomic levels given differences in taphonomic resistance between organisms. The effect of taphonomy was examined on trends in disparity of Paleozoic crinoids and blastozoans. Morphological characters were sequentially excluded from the analyses following progressive taphonomic degradation to determine how morphologic metrics changed in order to determine the strength of the potential bias. Blastozoans showed little change in these metrics with decreasing preservational quality, which is a result of a high number of characters that can be coded from isolated plates. The opposite result is present in crinoids, as the characters that are important in structuring the morphospace require intact series of plates to accurately assess. In addition, temporal trends in disparity could be recovered when taphonomic deterioration was exaggerated both within small-scale stratigraphic sequences as well as through the Paleozoic. Even though the taphonomic biases appear to be fairly minor, certain parts of a stratigraphic sequence should be avoided and morphological outliers could potentially play a larger role through time, though both of these issues can be easily identified and avoided. The methods presented in the current study produce way to assess how taphonomic processes can influence character-based studies of morphological diversity.