Comparison of taxonomic diversity, strontium isotope and sea-level patterns

Sepkoski's compendium of 28,730 marine genera was analyzed with a view toward comparing taxonomic diversity, strontium isotope stratigraphy and sea-level changes. The fossil record analyses discriminated between origination, extinction and pass through genera and collectively delineated changes in number of genera with time at the largely stratigraphic stage level. With notable exceptions of the Cretaceous and Tertiary, taxonomic diversity generally paralleled both strontium isotope stratigraphy and sea-level changes. Sampling bias was suggested in the Tertiary where an increase in genera numbers toward the Recent opposed the downward trends of both strontium isotope and sea level curves. The removal of all Recent genera from the Sepkoski database confirmed the bias in producing complimentary downward trends in all curves. Regression analysis of taxonomic diversity with respect to sea level extent and time duration explained 82% of the variability of the remaining data. Sea-level fluctuations are not always accompanied by significant changes in taxonomic diversity but strontium isotope analyses offers the potential of constraining the extent to which the magnitude of changes are associated with time duration.