PRELIMINARY ANALYSIS OF GENERIC LONGEVITY PATTERNS IN MISSISSIPPIAN CRINOIDS FROM EUROPE AND NORTH AMERICA

Generic longevities of five Mississippian crinoid clades were calculated using 11 time units within the Tournaisian, Visean, and Serpukhovian stages. Correlation between time units and Ma (Gradstein et al., 2005) was 0.994 (p = 0.00), justifying these 11 time units as a time proxy. Generic richness by clade was not a good predictor of mean longevity (r = 0.32, p = 0.37), suggesting consistent taxonomic practice between clades. For the clades (camerates, disparids, primitive cladids, advanced cladids, and flexibles), North American mean longevities were all greater than the European counterparts. This probably reflects the greater number of generic occurrences by time units in North America (559) versus Europe (183). Camerates had the longest mean longevity on both continents, suggesting a slower evolutionary turnover. This slower evolutionary turnover was accompanied by decreasing camerate generic richness through the Mississippian globally as this group waned during the end of the Middle Paleozoic Crinoid Evolutionary Fauna. Advanced cladids had the shortest mean generic longevity in North America with overall higher generic richness throughout the Mississippian as this group experienced rapid evolutionary turnover. For the entire Mississippian, advanced cladid generic richness greatly exceeded camerate generic richness on both continents. Disparids, primitive cladids, and flexibles were characterized by intermediate longevities and declining generic richness through the Mississippian, except for a spike during Time 9 in Europe for disparids and flexibles, although their total generic richness was well below the advanced cladids or camerates. Mean generic longevities between North American clades were not significantly different, except between camerates and advanced cladids (t-Test, p = 0.04). Further study will determine if this reflects an evolutionary pattern or taxonomic practice. Primitive cladids in Europe had a significantly shorter mean longevity than camerates, advanced cladids, and flexibles; probably a reflection of their relative rarity. In summary, it is evident that preservational bias has influenced the longevity data, yet there are patterns between clades and continents in need of further analysis.