Functional morphology and paleoecological implications of the platycrinitid column (Echinodermata, Crinoidea)

Abstract

Flume studies conducted on models and specimens of the helically twisted columns from Mississippian platycrinitid crinoids revealed two unique hydrodynamic interactions. Water is deflected up the column from levels near the sediment-water interface where food particles are more abundant. Turbulence, both in the lee and on the upstream side of the column, removes nutrient-poor water and replaces it with nutrient-rich water from near the sediment-water interface. Subsequently, the nutrient-rich water would have been filtered through the feeding apparatus of the crinoid. An upward deflection of as little as 10 percent bottom water would have resulted in a substantial increase in food particle load. Thus, the form of platycrinitid columns gave the crinoid a feeding advantage over otherwise similar crinoids of the same time period. The most diverse and abundant group of Mesozoic–Cenozoic stalked crinoids shows similar column modifications which suggests that the morphology may impart some competitive advantage to the organism.