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.

Many features of global diversity compilations have proven robust to continued sampling and taxonomic revision. Inherent biases in the stratigraphic record may nevertheless substantially affect estimates of global taxonomic diversity. Here we focus on short-term (epoch-level) changes in apparent diversity. We use a simple estimate of the amount of marine sedimentary rock available for sampling: the number of formations in the stratigraphic Lexicon of the United States Geological Survey. We find this to be positively correlated with two independent estimates of rock availability: global outcrop area derived from the Paleogeographic Atlas Project (University of Chicago) database, and percent continental flooding. Epoch-to-epoch changes in the number of formations are positively correlated with changes in sampled Phanerozoic marine diversity at the genus level. We agree with previous workers in finding evidence of a diversity-area effect that is substantially weaker than the effect of the amount of preserved sedimentary rock. Once the mutual correlation among change in formation numbers, in diversity, and in area flooded is taken into consideration, there is relatively little residual correlation between change in diversity and in the extent of continental flooding. These results suggest that much of the observed short-term variation in marine diversity may be an artifact of variation in the amount of rock available for study. Preliminary results suggest the same possibility for terrestrial data.Like the comparison between change in number of formations and change in sampled diversity, which addresses short-term variation in apparent diversity, the comparison between absolute values of these quantities, which relates to longer-term patterns, also shows a positive correlation. Moreover, there is no clear temporal trend in the residuals of the regression of sampled diversity on number of formations. This raises the possibility that taxonomic diversity may not have increased substantially since the early Paleozoic. Because of limitations in our data, however, this question must remain open.

The causes of mass extinctions and the nature of taxonomic radiations are central questions in paleobiology. Several episodes of taxonomic turnover in the fossil record, particularly the major mass extinctions, are generally thought to transcend known biases in the geologic record and are widely interpreted as distinct macroevolutionary phenomena that require unique forcing mechanisms. Here, by using a previously undescribed compilation of the durations of sedimentary rock sequences, I compare the rates of expansion and truncation of preserved marine sedimentary basins to rates of origination and extinction among Phanerozoic marine animal genera. Many features of the highly variable record of taxonomic first and last occurrences in the marine animal fossil record, including the major mass extinctions, the frequency distribution of genus longevities, and short-and long-term patterns of genus diversity, can be predicted on the basis of the temporal continuity and quantity of preserved sedimentary rock. Although these results suggest that geologically mediated sampling biases have distorted macroevolutionary patterns in the fossil record, preservation biases alone cannot easily explain the extent to which the sedimentary record duplicates paleobiological patterns. Instead, these results suggest that the processes responsible for producing variability in the sedimentary rock record, such as plate tectonics and sea-level change, may have been dominant and consistent macroevolutionary forces throughout the Phanerozoic.biodiversity ͉ mass extinction ͉ paleobiology ͉ sedimentary rock ͉ sequence stratigraphy O ne of the most striking aspects of the marine animal fossil record is that it preserves a volatile history of biodiversity and rates of taxonomic origination and extinction. Understanding the causes and evolutionary consequences of this volatility is one of the central goals of paleobiology. It has long been recognized, however, that the quantity of preserved sedimentary rock varies over short and long intervals of geologic time (1-3) and that this variation is correlated with several important macroevolutionary patterns in the fossil record, including changes in biodiversity (4-8) and rates of taxonomic extinction (4, 9, 10). The mutual correlations between preserved rock quantity and macroevolutionary patterns have been interpreted as evidence for either preservation biases that distort the apparent timings of extinction and origination in the fossil record (bias hypothesis) (4-7, 10) or a common pattern that is induced by processes, such as sea level fluctuations, plate tectonics, and resultant changes in marine shelf area, that affect both the amount of preserved rock and biological evolution (commoncause hypothesis) (6, 7, 9-12). Nevertheless, some workers have proffered that many intervals of turnover in the fossil record, particularly the major mass extinctions (13), are too substantial to be the result of preservation biases and are sufficiently distinct to require unique forcing mechanisms (14-17).Evaluati...

The Phanerozoic fossil record of marine animal diversity covaries with the amount of marine sedimentary rock. The extent to which this covariation reflects a geologically controlled sampling bias remains unknown. We show that Phanerozoic records of seawater chemistry and continental flooding contain information on the diversity of marine animals that is independent of sedimentary rock quantity and sampling. Interrelationships among variables suggest long-term interactions among continental flooding, sulfur and carbon cycling, and macroevolution. Thus, mutual responses to interacting Earth systems, not sampling biases, explain much of the observed covariation between Phanerozoic patterns of sedimentation and fossil biodiversity. Linkages between biodiversity and environmental records likely reflect complex biotic responses to changing ocean redox conditions and long-term sea-level fluctuations driven by plate tectonics.

The transition between the Proterozoic and Phanerozoic eons, beginning 542 million years (Myr) ago, is distinguished by the diversification of multicellular animals and by their acquisition of mineralized skeletons during the Cambrian period. Considerable progress has been made in documenting and more precisely correlating biotic patterns in the Neoproterozoic-Cambrian fossil record with geochemical and physical environmental perturbations, but the mechanisms responsible for those perturbations remain uncertain. Here we use new stratigraphic and geochemical data to show that early Palaeozoic marine sediments deposited approximately 540-480 Myr ago record both an expansion in the area of shallow epicontinental seas and anomalous patterns of chemical sedimentation that are indicative of increased oceanic alkalinity and enhanced chemical weathering of continental crust. These geochemical conditions were caused by a protracted period of widespread continental denudation during the Neoproterozoic followed by extensive physical reworking of soil, regolith and basement rock during the first continental-scale marine transgression of the Phanerozoic. The resultant globally occurring stratigraphic surface, which in most regions separates continental crystalline basement rock from much younger Cambrian shallow marine sedimentary deposits, is known as the Great Unconformity. Although Darwin and others have interpreted this widespread hiatus in sedimentation on the continents as a failure of the geologic record, this palaeogeomorphic surface represents a unique physical environmental boundary condition that affected seawater chemistry during a time of profound expansion of shallow marine habitats. Thus, the formation of the Great Unconformity may have been an environmental trigger for the evolution of biomineralization and the 'Cambrian explosion' of ecologic and taxonomic diversity following the Neoproterozoic emergence of animals.

Valentine and Moores [Valentine JW, Moores EM (1970) Nature 228:657-659] hypothesized that plate tectonics regulates global biodiversity by changing the geographic arrangement of continental crust, but the data required to fully test the hypothesis were not available. Here, we use a global database of marine animal fossil occurrences and a paleogeographic reconstruction model to test the hypothesis that temporal patterns of continental fragmentation have impacted global Phanerozoic biodiversity. We find a positive correlation between global marine invertebrate genus richness and an independently derived quantitative index describing the fragmentation of continental crust during supercontinental coalescence-breakup cycles. The observed positive correlation between global biodiversity and continental fragmentation is not readily attributable to commonly cited vagaries of the fossil record, including changing quantities of marine rock or time-variable sampling effort. Because many different environmental and biotic factors may covary with changes in the geographic arrangement of continental crust, it is difficult to identify a specific causal mechanism. However, cross-correlation indicates that the state of continental fragmentation at a given time is positively correlated with the state of global biodiversity for tens of millions of years afterward. There is also evidence to suggest that continental fragmentation promotes increasing marine richness, but that coalescence alone has only a small negative or stabilizing effect. Together, these results suggest that continental fragmentation, particularly during the Mesozoic breakup of the supercontinent Pangaea, has exerted a first-order control on the long-term trajectory of Phanerozoic marine animal diversity.paleogeography | paleobiology | biodiversity | biogeography

The causes of mass extinctions and the nature of biological selectivity during extinction events remain central questions in palaeobiology. Although many different environmental perturbations have been invoked as extinction mechanisms, it has long been recognized that fluctuations in sea level coincide with many episodes of biotic turnover. Recent work supports the hypothesis that changes in the areas of epicontinental seas have influenced the macroevolution of marine animals, but the extent to which differential environmental turnover has contributed to extinction selectivity remains unknown. Here I use a new compilation of the temporal durations of sedimentary rock packages to show that carbonate and terrigenous clastic marine shelf environments have different spatio-temporal dynamics and that these dynamics predict patterns of genus-level extinction, extinction selectivity and diversity among Sepkoski's Palaeozoic and modern evolutionary faunae. These results do not preclude a role for biological interactions or unusual physical events as drivers of macroevolution, but they do suggest that the turnover of marine shelf habitats and correlated environmental changes have been consistent determinants of extinction, extinction selectivity and the shifting composition of the marine biota during the Phanerozoic eon.

A new snake from Upper Cretaceous rocks in India is found with hatchling sauropod dinosaurs, demonstrating that large, gape-limited snakes were probably capable of taking in moderate-sized vertebrate prey.