Abstract
Morphological and environmental taphonomic gradient analysis provides insights into morphological, behavioral, and environmental influences on the preservation of fossil organisms. This paper explores morphological and environmental taphonomic gradients in six crinoid morphotypes (diplobathrids, monobathrids, dichocrinids, platycrinitids, cladids, and flexibles) from three stratigraphic units (the Maynes Creek Formation and the Starrs Cave and “Ollie” Members of the Wassonville Formation) representing distinct depositional environments along an onshore–offshore transect within the Early Mississippian (Kinderhookian) Wassonville Cycle of southeast Iowa. Taphonomic differences in stalk, calyx, and arm disarticulation, calyx compression, and arm orientation were categorized independently and subjected to a non-parametric ranking test with bootstrapping (rather than a parametric approach, due to the non-additive nature of the data analyzed herein) to explore taphonomic patterns. The results suggest that the disarticulation of the stalk, calyx, and arms behave independently, although patterns of arm disarticulation may be influenced by the disarticulation of the calyx. In general, preservational integrity in fossil crinoids appears to be a function of the relative proportion of articular to non-articular surface area, skeletal innovations, tissue type and properties, survival response behavior, and thickness and rapidity of burial. Furthermore, these results demonstrate a general decrease in preservational integrity from onshore to offshore environments in the Wassonville Cycle and that sedimentation dynamics associated with episodic events are more influential than background deposition in determining preservation in fossil Lagerstätten. The methodology employed herein also could be used effectively to identify morphological, behavioral, and environmental taphonomic influences on other fossil organisms.
