Randomness in the pattern of ‘mass extinctions’ and ‘waves of origination’

Abstract ‘Mass extinctions’ and ‘waves of origination’ are defined as peaks in the average probability of family extinction and origination per geologic stage, respectively. A simple neutral model is proposed, assuming only that the average probabilities of family extinction and origination have varied independently and had equal chances of going up and down from one stage to another. As a null hypothesis, this model is not rejected by the available palaeontologic data on marine animal and nonmarine invertebrate families in the Phanerozoic. The only discrepancy between the model and the empirical pattern is due to a systematic bias introduced by Fossil-Lagerstätten. The alleged periodicity of Late Phanerozoic mass extinctions follows inevitably from the model.