TAPHONOMY AS A GUIDE TO FUNCTIONAL-MORPHOLOGY OF HOLOCRINUS, THE FIRST POSTPALEOZOIC CRINOID

A taphonomic approach, in which patterns of fragmentation are used to infer the organization of soft tissue and function in crinoid stalks, was applied to pluricolumnals of the first post-Paleozoic crinoid, Holocrinus. The observed patterns are analogous to those for isocrinid crinoids, suggesting that Holocrinus and isocrinid stalks are functionally similar in having specialized sites for autotomy. Stalk autotomy in Holocrinus could not have been predicted based on morphological criteria alone: the stalk of Holocrinus lacks synostosial articulations, which among the isocrinids are the sites of autotomy. This implies that taphonomic data can supplement and sometimes supersede morphological data as a basis for functional reconstructions. Stalk autotomy in Holocrinus indicates that this trait was not derived independently by the isocrinids and comatulids, but rather that it was primitively shared by them. If pentacrinitids could not autotomize their stalks, as is likely, this would represent a loss of this ability through paedomorphosis.