TAPHONOMIC METHOD FOR DETERMINING MUSCULAR ARTICULATIONS IN FOSSIL CRINOIDS

A new taphonomic method is proposed and used to confirm that muscular tissue was present in the arms of Early Mississippian advanced cladid crinoids. The method relies on the assumption of differential tissue decay rates, with muscle decaying more rapidly than ligament. In a crinoid with muscular arms, the arms should disarticulate prior to disarticulation of the ligament bound column segments, whereas in a crinoid with only ligaments in the arms, the arms and column segments will begin to disarticulate at approximately the same time. This method provides an independent means to test for the existence of muscles, and it avoids some problems encountered by relying exclusively on morphological characters. The existence of muscles in the arms of Early Mississippian crinoids is consistent with the widely held view that crinoid muscular arm articulations first evolved during the Early Devonian.