It has previously been thought that there was a steep Cretaceous and Cenozoic radiation of marine invertebrates. This pattern can be replicated with a new data set of fossil occurrences representing 3.5 million specimens, but only when older analytical protocols are used. Moreover, analyses that employ sampling standardization and more robust counting methods show a modest rise in diversity with no clear trend after the mid-Cretaceous. Globally, locally, and at both high and low latitudes, diversity was less than twice as high in the Neogene as in the mid-Paleozoic. The ratio of global to local richness has changed little, and a latitudinal diversity gradient was present in the early Paleozoic.

The quantification of disparity is an important aspect of recent macroevolutionary stud ies, and it is usually motivated by theoretical considerations about the pace of innovation and the filling of morphospace. In practice, varying protocols of data collection and analysis have rendered comparisons among studies difficult. The basic question remains, How sensitive is any given dis parity signal to different aspects of sampling and data analysis? Here we explore this issue in the context of the radiation of the echinoid order Spatangoida during the Cretaceous. We compare pat terns at the genus and species levels, with time subdivision into subepochs and into stages, and with morphological sampling based on landmarks, traditional morphometries, and discrete char acters. In terms of temporal scale, similarity of disparity pattern accrues despite a change in tem poral resolution, and a general deceleration in morphological diversification is apparent. Different morphometric methods also produce similar signals. Both the landmark analysis and the discrete character analysis suggest relatively high early disparity, whereas the analysis based on traditional morphometries records a much lower value. This difference appears to reflect primarily the mea surement of different aspects of overall morphology. Disparity patterns are similar at both the ge nus and species levels. Moreover, inclusion or exclusion of the sister order Holasteroida and the stem group Disasteroida in the sampled morphospace did not affect proportional changes in spa tangoid disparity. Similar results were found for spatangoid subclades visa -vis spatangoids as a whole. The relative robustness of these patterns implies that the choice of temporal scale, morpho metric scheme, and taxonomic level may not affect broad trends in disparity and the representation of large-scale morphospace structure.

The taxonomic diversity of ammonoids, in terms of the number of taxa preserved, provides an incomplete picture of the extinction pattern during the Permian because of a strongly biased fossil record. The analysis of morphological disparity (the variety of shell shapes) is a powerful complementary tool for testing hypotheses about the selectivity of extinction and permits the recognition of three distinct patterns. First, a trend of decreasing disparity, ranging for about 30 million years, led to a minimum disparity immediately before the Permian-Triassic boundary. Second, the strongly selective Capitanian crisis fits a model of background extinction driven by standard environmental changes. Third, the end-Permian mass extinction operated as a random, nonselective sorting of morphologies, which is consistent with a catastrophic cause.