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.

Global diversity curves reflect more than just the number of taxa that have existed through time: they also mirror variation in the nature of the fossil record and the way the record is reported. These sampling effects are best quantified by assembling and analyzing large numbers of locality-specific biotic inventories. Here, we introduce a new database of this kind for the Phanerozoic fossil record of marine invertebrates. We apply four substantially distinct analytical methods that estimate taxonomic diversity by quantifying and correcting for variation through time in the number and nature of inventories. Variation introduced by the use of two dramatically different counting protocols also is explored. We present sampling-standardized diversity estimates for two long intervals that sum to 300 Myr (Middle Ordovician-Carboniferous; Late Jurassic-Paleogene). Our new curves differ considerably from traditional, synoptic curves. For example, some of them imply unexpectedly low late Cretaceous and early Tertiary diversity levels. However, such factors as the current emphasis in the database on North America and Europe still obscure our view of the global history of marine biodiversity. These limitations will be addressed as the database and methods are refined.

▪ Abstract Advances in taphonomy and stratigraphy over the past two decades have dramatically improved our understanding of the causes, effects, and remedies of incompleteness in the fossil record for the study of evolution. Taphonomic research has focused on quantifying probabilities of preservation across taxonomic groups, the temporal and spatial resolution of fossil deposits, and secular changes in preservation over the course of the Phanerozoic. Stratigraphic research has elucidated systematic trends in the formation of sedimentary gaps and permanent stratigraphic records, the quantitative consequences of environmental change and variable rock accumulation rates over short and long timescales, and has benefited from greatly improved methods of correlation and absolute age determination. We provide examples of how these advances are transforming paleontologic investigations of the tempo and mode of morphologic change, phylogenetic analysis, and the environmental and temporal analysis of macroevolutionary patterns.

In several increasingly realistic steps, a model of the stratigraphic distribution of fossils is presented. The first and simplest step assumes that if a taxon was extant it will have been preserved. The second step admits that if a taxon was extant, there is some probability less than one that it will have been preserved. This step produces randomly distributed gaps, and fossil ranges that are somewhat shorter than the span of time in which a taxon actually lived. The third step assumes facies-controlled taxa and parasequence-style cyclicity. This produces randomly and nonrandomly distributed gaps, including the anomalously long gaps recognized in confidence limit studies. The final model incorporates depositional sequences and indicates that first and last occurrences will cluster at sequence boundaries and at flooding surfaces in the transgressive systems tract. Across-shelf gradients in diversity, taphonomy, or eurytopy can control the strength, but not the stratigraphic position of these peaks. Comparison of the model to data from the Upper Ordovician suggests that these modeled features are present in the fossil record. Many previously studied paleobiologic patterns may be, at least in part, an artifact of facies control and sequence architecture. Such patterns include gradual or stepwise mass extinction, punctuated morphologic and taxonomic change, iterative evolution, and the replacement of shallow water faunas by deeper water faunas at biomere boundaries.

Recent studies have emphasized that faunal change is typically brief and most commonly occurs at sequence boundaries and major flooding surfaces. The Upper Ordovician of the Cincinnati, Ohio, region records a major biotic invasion in the Richmondian Stage, which offers an opportunity to test these generalizations and to understand how episodes of faunal change are reflected in the structure of ecological gradients. The early Cincinnatian (C1–early C4 depositional sequences) displays two relatively stable faunal gradients, with the primary gradient reflecting onshore-offshore setting and the secondary gradient reflecting substrate consistency. During the mid-C4 sequence, dominant taxa of the shallow subtidal are extirpated, while deep subtidal taxa expand into those habitats, leading to a loss of cross-shelf faunal differentiation. This faunal breakdown is accompanied into the mid-C5 by a series of ecological epiboles, indicating an ongoing flux in ecological associations. The onshore-offshore gradient is reestablished in the C5, albeit with new associations dominated by or containing immigrant taxa. Recognition of this gradient is hindered by widespread increased abundance of bryozoans and by the delayed appearance of at least seven common genera of brachiopods and corals. The Richmondian Invasion plays out over multiple sequences and is not confined to a brief interval at the beginning of a sequence. These faunal changes do not coincide with sequence boundaries or major flooding surfaces and therefore cannot be sequence stratigraphic artifacts, nor can they represent a geologically instantaneous faunal response to sea-level change.