MECHANISMS RESPONSIBLE FOR THE INCREASE IN THE TAXONOMIC DIVERSITY IN THE PHANEROZOIC MARINE BIOTA

Abstract

Taxonomic diversity dynamics traditionally interpreted using exponential or logistic models of diversification, both of which are based on the assumption that the rate of origination (and sometimes also the rate of extinction) depends on the level of taxonomic diversity. Paleontological data, however, give inadequate support for this assumption. Therefore, an alternative model is suggested: the generic origination rate is stochastically constant and does not depend on the diversity level; genera differ in their vulnerability; the extinction probability for each genus during each time interval depends on its vulnerability only. Apparently, the most important factor of the increase in diversity in marine biota during the Phanerozoic was a stepwise increase in the mean generic durations. There were four such steps: Cambrian, Ordovician-Permian, Mesozoic, and Cenozoic. This stepwise increase in generic durations was partly due to the successive replacement of dominating groups, but to a larger extent, it was due to the generic durations that increased within each group at each successive step.