DEMISE OF THE MIDDLE PALEOZOIC CRINOID FAUNA - A SINGLE EXTINCTION EVENT OR RAPID FAUNAL TURNOVER

Macroevolutionary change from the Middle to the Late Paleozoic crinoid fauna was not the result of mass extinction. The presumption that the decline of the middle Paleozoic crinoid fauna was from a single mass extinction event was tested using seriation, multidimensional scaling (MDS), binomial analysis, and bootstrapping simulations on a data set which is a comprehensive revision of old faunal lists. The data for th ese analyses were based on temporal distributions of 214 species from 69 late Osagean and early Meramercian localities from the midcontinent al United States. The time under consideration is subdivided into seve n informal intervals using MDS in conjunction with biostratigraphy. Se riation of species ranges into these intervals results in a gradual pa ttern of faunal turnover, and sampling bias can be eliminated as a cau se for this more gradual pattern. MDS analysis of the crinoid range da ta is similar to MDS simulations using data with continuous, monotonic species turnover and dissimilar to a simulated mass extinction. Binom ial analysis and bootstrapping demonstrate that the observed number of extinctions at the putative extinction boundary were not unusually hi gh. All methods agree that extinctions throughout this time were high but spanned several time intervals and that rapid, monotonic faunal tu rnover describes the data better than mass extinction. Macroevolutiona ry processes other than mass extinction and microevolutionary processe s must have dictated the character and composition of this remarkable faunal transition among the Crinoidea.