Rates of anagenetic evolution and selection intensity in Middle and Upper Ordovician species of the bryozoan genus Peronopora

Evolutionary rates and selection intensities in eight cladistically defined species-level evolutionary sequences of the Middle and Upper Ordovician bryozoan genus Peronopora were calculated for comparison with values published for fossil and living taxa. Calculations were restricted to statistically significant unidirectional segments of anagenetic series to minimize the mixing of different modes, directions, and rates of evolutionary change. Rates and selection intensities ranged from 10^−7 to 10^−6 darwins and from 10^−6 to 10^−5 haldanes. Across characters, the weighted mean evolutionary rate equaled 5.86 × 10^−7 darwins and the mean selection intensity was 6.44 × 10^−7. Mean rates of 2.15 × 10^−6, 4.31 × 10^−6, and 8.61 × 10^−6 haldanes, and corresponding mean selection intensities equaling 2.39 × 10^−6, 4.78 × 10^−6, and 9.56 × 10^−6, were calculated for generation lengths of 0.5, 1, and 2 years, respectively. The magnitudes of positive and negative evolutionary rates and selection...