Biodynamic and phyletic paradigms for sensory organs in camerate crinoids

Functional analysis of thecal pores and associated fixed pinnules of camerate crinoids reveals that they may have been organized into an integrated current‐sensing biologic system. Paleobiologic, biodynamic, and geometric evidence reveals a potential for sensing the direction and intensity of horizontal water currents. An ahistoric paradigm predicts that the inferred sensory organs could have elicited several alternative feeding postures and a survival posture in response to current intensity. Possession of long anal tubes is judged to be related to the sensory function. By virtue of these adaptations certain camerates may have been discriminatory rheophilic feeders in complex fdter feeding communities. An historically founded phyletic paradigm suggests that a functional change in thecal pores and pinnules occurred in the Early Mississippian as an evolutionary concourse in several independent lineages. This specialized sensory innovation may have signifcantly contributed to the ‘flowering’ of camerates in rheic carbonate environments as well as their demise in terrigenous clastic environments. Phyletic paradigms illustrate the advantage of functional analysis of fossil structures at several points in time and especially at the acme of development when structure and function are commonly most clearly delimited.