English: Morphological evolution of Xandarellida derived from results of phylogenetic analyses and proposed model for cephalic evolution. Note that other character optimization options are plausible, but result in either an equal or greater number of character transformations. a Topology based on maximum parsimony with implied weights (see Fig. 9a, b). b Topology based on Bayesian inference (see Fig. 9c). Abbreviations: diff. ex., differentiated exopod; red. Reduced