Understanding the early morphological diversification of crinoids depends in part on the origin of the Crinoidea, but there are opposing hypotheses regarding the role and/or position of the well-established crinoids, i.e. the “Ordovician Crown Group Crinoids” (OCG crinoids):

(I) Did the basal crinoid have multiple, irregular plates so that the only early evolutionary trend was plate reduction?

(II) Did the basal crinoid have four circlets, as in the aethocrinids, so that early evolutionary trends included both plate addition and reduction?