CRINOID STALK FLEXIBILITY - THEORETICAL PREDICTIONS AND FOSSIL STALK POSTURES

Flexibilities in Lower Mississippian crinoid stalks were inferred from preserved postures and shown not to conform with predictions of a can tilever beam model. Flexibilities were not correlated with hard-part c haracters such as stalk diameter, stalk length, or columnal height. Th e lack of correspondence between the predictions of the cantilever mod el and observed flexibilities implies that the most likely control of stalk flexibility is the ligament, more specifically, its non-constant , mutable properties. Although a few Lower Mississippian crinoids, suc h as Gilbertsocrinus, Platycrinites, and Camptocrinus, have enhanced f lexibility achieved by radical modifications of columnal facet morphol ogy, this study has failed to identify any general morphological chara cters that consistently predict flexibility. It appears that skeletal morphology is a poor guide to stalk flexibility; mutable collagenous t issue is the key.