THE ROOT OF THE PROBLEM: PALEOECOLOGY OF DISTINCTIVE CRINOID ATTACHMENT STRUCTURES FROM THE SILURIAN (WENLOCK) OF GOTLAND

The holdfast (attachment structure) is perhaps the most understudied aspect of the paleoecology of the endoskeleton of fossil crinoids. A new collection of well-preserved holdfasts from a recently reopened quarry at Hunninge, Gotland, in Homerian (upper Wenlock) strata of the Klinteberg Formation, includes several morphologies, the commonest being terminal dendritic radicular holdfasts (TDRHs). These specimens are probably the attachment structure of the cladid Enallocrinus, of which there are two nominal species in this formation. These attachments have a consistent morphology of five, equally spaced, long radices that spread across the sea floor. These crinoids were gregarious and TDRHs in a group commonly show the same radice orientations. The radices have a large axial canal compared to those of modern crinoids; each included, at least, some nervous tissues. Taken together, these features suggest that, apart from attachment, these distinctive TDRHs may have served a sensory function. Other holdfasts in this assemblage also show monospecific aggregations, perhaps suggesting biochemical attraction such as that shown by certain other sessile invertebrates such as barnacles.