Exploring rates of change and modes of evolution in blastozoan echinoderms

Abstract Over the past half century, paleobiologists have advanced the estimation of phylogenetic relationships among fossil taxa to explore evolutionary patterns in deep time. This study employs a breadth of phylogenetic analyses, specifically divergence time estimations and character rate evolution, within three blastozoan echinoderm clades: Diploporita, Eublastoidea, and Paracrinoidea. Utilizing reversible jump Markov chain Monte Carlo (rjMCMC) and fossilized birth–death (FBD) models, we investigated evolutionary rates through anatomical subunit partitioning. Results suggest similar rates among the three groups, although Paracrinoidea exhibits elevated rates in several anatomical subunits. The inferred trees largely agree with other recently published analyses, in that the current taxonomy of the group does not reflect true evolutionary relationships. Thus, this study adds to a growing body of literature that highlights the need to revise echinoderm taxonomy. We tested different clock models for each group and found that model choice had strong effects on resulting trees; our findings suggest linked clocks (i.e., the same clocks for all character partitions) had more support than unlinked clocks (i.e., different clocks for different character partitions). These findings indicate a need to carefully consider model choice and rates of evolution when utilizing these types of analyses.