Morphological paradox of disparid crinoids (Echinodermata): phylogenetic analysis of a Paleozoic clade

Phylogenetic relationships within the parvclass Disparida are evaluated using parsimony-based phylogenetic methods. The Disparida is a combination of forms with simplified morphologies and forms with highly specialized morphologies. The latter, e.g., Acolocrinidae, Calceocrinidae, Catillocrinidae, and Myelodactylidae, are consistently identified as clades, as are some simplified forms, such as the Allagecrinidae, Eustenocrinidae, and Tetragonocrinidae. The Iocrinidae is typically recovered as a paraphyletic grade between the outgroup the oldest disparid, Alphacrinus, and more tipward disparids. The primary aspects of disparid phylogeny that remain ambiguous using parsimony analysis are the Cincinnaticrinidae and Homocrinidae, each of which is broadly paraphyletic with taxa in basal and/or derived positions, the status of several monogeneric families, and the phylogenetic position of disparids too poorly known to include in phylogenetic analysis.