EVALUATING MORPHOLOGICAL CONVERGENCE VERSUS CONSERVATISM ACROSS THE DIPLOBATHRID CRINOID PHYLOGENY
It has been recently established that the subclass Diplobathrida, a long-lived (Ordovician-Mississippian) group of camerate crinoids, is a monophyletic group, and a robust phylogeny for the clade has been recovered. This makes diplobathrid crinoids a useful model group for exploring patterns of morphologic evolution and quantitatively assessing hypotheses of evolutionary trends. For example, it has been suggested that evolutionary convergence and/or parallelism in overall calyx design was widespread among crinoids, although this has not been tested within a phylogenetic framework. Similarly, patterns of convergence versus conservatism of individual calyx characters are poorly understood.
Here, I revisit long-standing questions regarding the evolutionary origin of calyx designs using diplobathrid crinoids. The diplobathrid tree topology is time-scaled using the cal3 method of Bapst (2013). A combination of parsimony-based and maximum likelihood-based ancestral state reconstruction along with Bayesian stochastic character mapping are applied to time-scaled trees to determine the ancestral states of characters, the frequency of character transformations, and whether characters related to calyx design are labile or conserved.