Myelodactylid crinoid columnals from the Lower Visby Beds (Llandoverian) of Gotland

The distinctive columnals of myelodactylid crinoids from the Upper Llandovery of Gotland show a wide range of morphologies. This indicates that myelodactylids were more diverse during the Silurian than is indicated by the fossil record of more complete specimens. Although unattached, myelodactylids were not free-swimming (as has previously been suggested), a conclusion supported by comparison with modern crinoids, gross myelodactylid morphology and an SEM study of columnal microstructure. Rather, genera such as Myelodactylus and Herpetocrinus probably lay on the unconsolidated sediment surface with the coiled stem and cirri enclosing the crown.