Patterns of biotic change in Middle Jurassic to Early Cretaceous Tethyan Radiolaria

The rate of taxic turnover of nearly 400 radiolarian species/subspecies is analyzed in order to document long term biotic change of plankton during th e Middle Jurassic to Early Cretaceous (Aalenian to Aptian). The pattern and dynamic of diversity change is described using four indices: rate of speci es first and last occurrence, rate of diversification and rate of turnover. Plots of cumulative sampling effort suggest that the analyzed data represe nt an adequate sample of total standing diversity for most examined stages. Rates of species first occurrence exceed rates of last occurrence for most of the Middle Jurassic, except for the middle Bajocian. In contrast, the L ate Jurassic was a time of decreasing radiolarian diversity and the Kimmeri dgian records the lowest rate of diversification, It is followed by a drama tic increase in first occurrences near the Jurassic-Cretaceous boundary wit h as a result the highest rate of diversification recorded in the late Tith ortian. Regional radiolarian diversity was stable throughout most of the Ea rly Cretaceous. A stratigraphic permutation test was performed to assess th e influence of uneven sampling on the observed pattern of taxic turnover an d identified the intervals for which randomly obtained patterns are signifi cantly different from the observed pattern. The Kimmeridgian and late Titho nian events coincide with substantial climate-derived perturbations in wate r cycling, nutrient supply and oceanic productivity. They point to a negati ve relationship between radiolarian macroevolution and changes in the state of nutrient availability, although further work is needed to refine the te mporal resolution of this relationship and to explore ecological aspects of its causal link with respect to radiolarian evolution. (C) 2001 Elsevier S cience B.V. All rights reserved.