THE IMPORTANCE OF CHARACTER CHOICE IN QUANTIFYING MORPHOLOGY IN EARLY PALEOZOIC CAMERATE CRINOIDS

The quantification of disparity, or morphological diversity, is highly dependent on the methodology used, particularly the choice of discrete characters. We examine how character choice influences disparity within early Paleozoic crinoids, specifically the subclass Camerata. We examined 200 crinoids (including ~70 camerates) and coded them using two different sets of characters. The first is a well-studied character set and the later was compiled for the Assembling the Echinoderm Tree of Life Project (AEToL) which consisted of seventy percent more characters including morphology from the tegmen and oral surface that was not included in the previous dataset. A morphospace was constructed using principal coordinate analysis and disparity was calculated throughout the Early Paleozoic. The resulting morphospaces from the two datasets were different in both the characters that defined the primary axes and particularly in the grouping of the orders within the camerates. While the earlier character set separated monobathrid and diplobathrid camerates based on the presence of an infrabasal circlet, the two groups heavily overlap in the AEToL dataset. This is in contrast to the two clades of inaduate crinoids that show distinctive morphologies beyond the presence or absence of an infrabasal circlet. Despite this difference, the primary structure of the morphospace was retained in terms of the relative distance between taxa. The general crinoid disparity pattern for the AEToL dataset is very similar to the previous study, especially within the Ordovician. In the Silurian, there are significant differences in disparity between the two datasets, with the AEToL dataset lacking a morphological recovery following the Late Ordovician mass extinction. Inaduates expand morphologically following this event, but the new dataset shows an overall decrease in disparity throughout the Early Silurian, which is largely caused by a contraction in the diversity of morphologies seen within the camerates.