SURVIVORSHIP ANALYSIS OF PALEOZOIC CRINOIDEA - EFFECT OF FILTER MORPHOLOGY ON EVOLUTIONARY RATES

The evolutionary rates of Paleozoic Crinoidea were obtained using dyna mic survivorship analysis. The stratigraphic ranges of 838 genera were used in the analyses, revealing a mean generic duration of 12.0 m.y. and a mean species duration of 6.7 m.y., values within the range of lo ngevities reported for other taxa. Further analyses showed differences in evolutionary rates among crinoid taxa: camerate species and genera were shorter-lived than species and genera of flexibles and inadunate s. This pattern may result from ecological differences among these tax a: an energy budget equation solved for crinoids with various filter m orphologies revealed that crinoids with fine-mesh filters require high er current velocities to supply them with sufficient particulate nutri ents than do crinoids with coarse-mesh filters. A hypothesis stipulati ng that these differences control the distribution of crinoids among d ifferent environments is supported by patterns of occurrence of Missis sippian crinoids: the pinnulate camerates (fine filter) dominate highe r energy settings while the non-pinnulate inadunates and flexibles (co arse filter) are found in all environments. The ''specialized'' pinnul ate crinoids may therefore be more prone to speciation and extinction than the non-pinnulate ''generalists,'' thus accounting for the observ ed differences in the evolutionary rates of the three subclasses. The above hypothesis was tested by comparing evolutionary rates of two mor phological groups: fine-filtered crinoids (camerates) and coarse-filte red crinoids (non-pinnulate Paleozoic crinoids). As predicted, fine-fi ltered taxa had higher extinction and origination rates. A ''bootstrap ping'' technique revealed that the differences in extinction rates wer e significant at the p < 0.10 level.