Abstract Two prominent patterns have been recognized in Phanerozoic extinction data: (1) a quasi-periodic distribution of extinction-intensity peaks, and (2) a linear, declining background extinction intensity gradient. Characterization and interpretation of both patterns are necessary to understand Phanerozoic extinction controls. The extinction-intensity peak spectrum has been variously interpreted as a reflection of the time-series of major sea-level regressions, continental flood-basalt province (CFBP) eruptions, and bolide impacts. In order to evaluate the level of association between these time-series and the Phanerozoic marine invertebrate extinction record statistically, a new Monte Carlo simulation strategy is presented. Results of simulation-based tests suggest that the time-series of major, eustatic sea-level regressions and CFBP eruption events have a statistically significant ( p ≤ 0.05) association with Tatarian-Pliocene, stage-level, extinction intensity peaks. Associations between this peak series and the time-series of crater-producing bolide impacts do not appear significant at this level. A limited multicausal event scenario was also tested using the Monte Carlo method, and recognized the combination of sea-level regression and CFBP volcanism to be significantly associated with the largest extinction intensity peaks of the last 250 Ma. The background extinction-intensity gradient has been interpreted variously as: (1) an indicator of progressive improvement in extinction resistance through selection; (2) the by-product of an invasion of marginal (extinction-resistant) habitats; and (3) as a taxonomic-stratigraphical artefact. Results of subdivided linear trend analyses suggest that the background extinction-intensity gradient is largely confined to the Late Palaeozoic-Cenozoic interval. No statistically significant gradient is present in the most recent compilation of Early-Middle Palaeozoic data on marine, invertebrate extinctions. The timing of gradient initiation and extinction variance analyses suggest that reorganization of global carbon cycles and oceanographical circulation patterns in the Devonian-Early Carboniferous, and the evolutionary appearance of modern phytoplankton groups in the Late Triassic both had dramatic effects on the character of the extinction-intensity gradient.

A series of iridium anomalies and microtektite-bearing layers indicative of extraterrestrial impact events have been found in late Eocene sediments in the deep sea. Previously, these deposits had been reported to be approximately synchronous with major extinction events in groups of both terrestrial and marine organisms. High-resolution biostratigraphic studies, though, have failed to find any direct evidence for association between impact-derived materials and species extinctions in individual stratigraphic sequences. In addition, stable isotopic studies of the deep-sea record reveal abundant evidence for an episode of major climatic change beginning in the middle Eocene and continuing through the Oligocene. A new analysis of patterns of taxic richness, extinction rates, and origination rates in 17 Eocene through Oligocene planktic foraminiferal biozones indicates that relatively high numbers of planktic foraminiferal taxic extinctions are not confined to the Eocene/Oligocene boundary, or to biozones containing impact ejecta (e.g., microtektite layers, Ir anomalies). Instead, virtually all middle Eocene through middle Oligocene biozones are characterized by broadly comparable numbers of taxic extinctions. However, analysis of relative abundances of individual species and patterns of morphometric variation in middle and late Eocene populations of planktic foraminifera suggest that impacts may have had substantial and long-lasting effects on the dynamics of local populations within areas of direct environmental perturbation. In order to understand the local biotic effects and potential evolutionary role of events such as extraterrestrial impacts, it is important that detailed analyses of species- and population-level patterns of morphological variation and faunal turnover proceed in concert with coarser grained investigations so that patterns of variation can be compared on a wide variety of taxonomic and stratigraphic scales (e.g., species-level versus family-level taxonomic resolution, biozone-level versus stage-level stratigraphic resolution).