Paleobiology Database Research Articles

Towards community-driven paleogeographic reconstructions: integrating open-access paleogeographic and paleobiology data with plate tectonics

Abstract. A variety of paleogeographic reconstructions have been published, with applications ranging from paleoclimate, ocean circulation and faunal radiation models to resource exploration; yet their uncertainties remain difficult to assess as they are generally presented as low-resolution static maps. We present a methodology for ground-truthing the digital Palaeogeographic Atlas of Australia by linking the GPlates plate reconstruction tool to the global Paleobiology Database and a Phanerozoic plate motion model. We develop a spatio-temporal data mining workflow to validate the Phanerozoic Palaeogeographic Atlas of Australia with paleoenvironments derived from fossil data. While there is general agreement between fossil data and the paleogeographic model, the methodology highlights key inconsistencies. The Early Devonian paleogeographic model of southeastern Australia insufficiently describes the Emsian inundation that may be refined using biofacies distributions. Additionally, the paleogeographic model and fossil data can be used to strengthen numerical models, such as the dynamic topography and the associated inundation of eastern Australia during the Cretaceous. Although paleobiology data provide constraints only for paleoenvironments with high preservation potential of organisms, our approach enables the use of additional proxy data to generate improved paleogeographic reconstructions.

Habitat breadth and geographic range predict diversity dynamics in marine Mesozoic bivalves

Numerous environmental and intrinsic biotic factors have been sought to explain patterns in diversity and turnover. Using taxonomically vetted and sampling-standardized data sets of more than 50,000 taxonomic occurrences in the Paleobiology Database (PaleoDB) we tested whether habitat breadth predicts genus durations and diversity dynamics of marine Mesozoic bivalves, and whether this effect is independent of the well-known positive relationship between geographic range and longevity. We defined the habitat breadth of a genus as a function of its realized ranges in water depth, substrate type, and grain size of the substrate. Our analysis showed that mean values of extinction and origination rates are significantly higher for narrowly adapted genera compared to broadly adapted genera, with differences being evident in all analyzed stratigraphic intervals. Linear models showed that both geographic range and habitat breadth have an independent effect on genus durations and on diversity dynamics. These results reaffirm the role of geographic range and furthermore suggest that habitat breadth is an equally important key predictor of extinction risk and origination probability in Mesozoic marine bivalves. Habitat generalists, regardless of their geographic range, are generally less prone to extinction. Conversely, widely distributed genera that are more specialized may be more endangered than one would expect from their geographic range alone. Extinction rates tend to be higher for specialized genera in both background and mass extinctions, suggesting that wide habitat breadth universally buffers against extinction. The trajectories of origination rates through time differ from those of extinction rates. Whereas there is no pronounced ecological selectivity in origination in the Triassic and most of the Jurassic, Cretaceous origination rates are higher for specialized genera. This may best be explained by diversity-dependence. When diversity levels reach a critical point a further increase in diversity is achieved by elevated origination rates of more specialized forms.

The sampling and estimation of marine paleodiversity patterns: implications of a Pliocene model

Data that accurately capture the spatial structure of biodiversity are required for many paleobiological questions, from assessments of changing provinciality and the role of geographic ranges in extinction and originations, to estimates of global taxonomic or morphological diversity through time. Studies of temporal changes in diversity and global biogeographic patterns have attempted to overcome fossil sampling biases through sampling standardization protocols, but such approaches must ultimately be limited by available literature and museum collections. One approach to evaluating such limits is to compare results from the fossil record with models of past diversity patterns informed by modern relationships between diversity and climatic factors. Here we use present-day patterns for marine bivalves, combined with data on the geologic ages and distributions of extant taxa, to develop a model for Pliocene diversity patterns, which is then compared with diversity patterns retrieved from the literature as compiled by the Paleobiology Database (PaleoDB). The published Pliocene bivalve data (PaleoDB) lack the first-order spatial structure required to generate the modern biogeography within the time available (<3 Myr). Instead, the published data (raw and standardized) show global diversity maxima in the Tropical West Atlantic, followed closely by a peak in the cool-temperate East Atlantic. Either today's tropical West Pacific diversity peak, double that of any other tropical region, is a purely Pleistocene phenomenon—highly unlikely given the geologic ages of extant genera and the topology of molecular phylogenies—or the paleontological literature is such a distorted sample of tropical Pliocene diversity that current sampling standardization methods cannot compensate for existing biases. A rigorous understanding of large-scale spatial and temporal diversity patterns will require new approaches that can compensate for such strong bias, presumably by drawing more fully on our understanding of the factors that underlie the deployment of diversity today.

Determinants of early survival in marine animal genera

Genera by their very nature are expected to be monotypic and geographically and environmentally restricted at their origin, and most genera do not endure past their stage of first appearance. At the same time, those genera that do endure have a capacity to expand greatly in geographic range, environmental breadth, and species richness. Here we ask what it is that allows some genera and not others to survive past their inception. Using occurrence data from the Paleobiology Database, we find that initial geographic range has the strongest effect on survival, followed by environmental breadth, with the effect of species richness weaker on average. The effect of geographic range is strongest if measured as the distances spanned by the occurrences of a genus rather than the number of distinct areas in which a genus lives. We document substantial secular variation in selectivity of early survival. The most striking aspect of this variation is that survival is only weakly selective among genera that first appear during the Mesozoic. By following genera beyond their stage of first appearance, we find that selectivity with respect to all factors becomes systematically stronger as cohorts age and genera become more differentiated in range, breadth, and richness. This may help account for a previously identified statistical effect of genus age on the chances of survival.

Predicting extinction from fossil trajectories of geographical ranges in benthic marine molluscs

AbstractAimThe geographical ranges of marine taxa wax and wane in a nearly symmetrical fashion over their durations. We use this pattern as well as the age distribution of genera to predict the time of extinction of extant genera of benthic marine molluscs.LocationA global occurrence database (Paleobiology Database) of fossil marine molluscs from the Mesozoic and Cenozoic eras was used for this study.MethodsFor the geographical range method, we determined the average trajectories of geographical range size for extinct genera of bivalves and gastropods. The maxima of these trajectories were used as landmarks for predicting the time of extinction for extant genera. Prediction was done by cross‐multiplication, using the time elapsed until the maximum was reached and the position of the landmark. For the duration–frequency method, we calculated the time of extinction based on probabilities derived from the frequency distribution of stratigraphic ranges (durations) of all extinct genera. The accuracy and precision of predictions were tested with extinct genera and then applied to extant genera.ResultsOn average, bivalve and gastropod extinct genera reached their maximum geographical range size at 62% and 50% of their total duration. The accuracy of predictions ranged from −3.1 to 11.0 million years (Myr) for both groups, and the precision ranged from 13.6 to 19.5 Myr. Only a small subset of extant genera was suitable for prediction with the geographical range method, mainly because the geographical ranges of most extant genera are still rising on geological time‐scales. The second method provided a similar prediction quality, but showed a substantial decrease in quality when predicting long‐duration (> 100 Myr) genera.Main conclusionsThe mean probability for an accurate prediction using the geographical range approach is 57% with a precision of ± 15 Myr. Prediction is possible only for genera whose peak geographical range has already elapsed (17% of extant bivalves, 16% of extant gastropods). The duration–frequency approach does not have this prerequisite and is therefore applicable to many more genera, but prediction quality declines with duration. The two methods therefore complement each other and can supplement the various efforts used to estimate extinction risk.

Diversity dynamics of echinoderms and evolution of marine communities

A compound analysis of two global paleontological databases (Sepkoski’s database (SDB) and The Paleobiology Database) allowed the recognition of a number of previously undescribed trends in the evolution of the phylum Echinodermata. Paleozoic echinoderms, dominated by sessile epibenthic filter feeders, played an important role in benthic communities, especially in the Ordovician and Carboniferous. Paleozoic echinoderms typically showed an increased rate of genus renewal, which significantly decreases in the Meso-Cenozoic. After the P-T crisis the echinoderms became dominated by motile taxa, while the role of infaunal forms increased. During the global turnover in the benthic communities at the K-T boundary, which was accompanied by a sharp increase in the mean alpha-diversity, many marine organisms became inhabitants of much richer (compared to the Mesozoic) communities. However, of all echinoderms, this trend is observed only in crinoids. In contrast to most large taxa, echinoderms do not show positive correlation between the duration of genera and alpha-diversity of communities, which included these genera. During the Phanerozoic the geographical distribution of echinoderms showed a sharp paleolatitudinal gradient, i.e., each period was characterized by one paleolatitudinal zone with the maximum diversity of echinoderms, and the diversity rapidly decreasing to the north and to the south of this zone. The zone of the maximum diversity of echinoderms, like of entire marine biota, during the Phanerozoic gradually moved from the tropics of the southern hemisphere to the middle latitudes of the northern hemisphere.

Contrasting patterns and connections of rock and biotic diversity in the marine and non-marine fossil records of North America

Macrostratigraphy uses packages of continuous sedimentation that are bound by hiatuses of non-deposition, erosion, or alternations between environments/lithologies to characterize spatiotemporal patterns of sedimentation. Previous work has linked the macrostratigraphy of marine shelf environments to many different macroevolutionary patterns in the marine animal fossil record. Here we use an improved macrostratigraphic database for North America, combined with fossil occurrence data in the Paleobiology Database, to show that macroevolutionary and macrostratigraphic patterns are correlated more strongly in marine environments than in non-marine environments. We also test the hypothesis that the temporal distribution of lithological diversity (measured as evenness, similar to ecological evenness based on the number of lithostratigraphic units with a given lithologic type within each time interval) has a relationship to genus-level taxonomic diversity in both the marine and non-marine realms. Uneven sampling of lithologies and their corresponding depositional environments can bias our perception of taxonomic diversity by causing taxa from poorly sampled environments to be underrepresented in the fossil record. Our results show a negative correlation between lithologic evenness and marine vertebrate generic richness — less even sampling of lithologies corresponds to a higher observed taxonomic richness, and no correlation with lithologic evenness and non-marine diversity measures. This suggests a difference in the relationship between biologic and sedimentary processes at work in the marine and non-marine realms, and possibly differences in the magnitude of the bias imposed by the rock record on the underlying biologic patterns.

REGIONAL-SCALE MARINE FAUNAL CHANGE IN EASTERN AUSTRALIA DURING PERMIAN CLIMATE FLUCTUATIONS AND ITS RELATIONSHIP TO LOCAL COMMUNITY RESTRUCTURING

Marine invertebrates are at risk of extinction if climate changes outpace their ability to adapt to thermal stress, and cold-adapted taxa may be especially vulnerable because of their specialized physiologies and because their high-latitude distributions permit only limited poleward migration. Here, we use a database of 1437 early and middle Permian eastern Australian fossil collections from the Paleobiology Database to test for latitudinal range shifts, extinctions, and faunal invasion among high-latitude marine invertebrates during climate changes in the late Paleozoic ice age. Latitudinal range shifts are not apparent, either because genera were unable to migrate or, more likely, because sampling noise or the scale of analyses prevent their recognition. Extinction rates were moderately elevated during the largest climate shifts, however, possibly suggesting that at least some taxa were unable to respond to the rate or magnitude of climate change. Although recognition of range shifts within Australia is difficult, warm-water brachiopods, bivalves, and ammonoids invaded the region during pronounced warming in the Artinskian, highlighting the importance of temperature on faunal distribution. That faunal invasion was coincident with substantial restructuring of local paleocommunities, but both likely resulted from the common cause of increasing temperature rather than having a causal relationship. Temperature warming would have stressed cold-adapted stenotherms, triggering changes in local dominance and allowing immigration of warm-water taxa. These local and regional shifts in dominance and distribution imply that physiological stresses from even gradual climate change can be sufficient to trigger biotic change.

Perception of paleocommunities at different taxonomic levels: How low must you go?

To obtain meaningful information from paleocommunities, researchers must collect assemblages that are sufficiently complete to accurately represent the once-living community and large enough to produce statistically robust results. A key decision in community paleoecological research is the level of taxonomic identification. Here, we conducted a meta-analysis of 28 datasets from the Paleobiology Database (PBDB) to determine whether paleocommunity analyses at higher taxonomic levels produce similar results to those analyzed at the generic level. For each dataset, we composed taxon-sample matrices (series of samples containing multiple taxa of varying abundances) at the genus-, family-, order-, and class-levels. We then compared the multivariate paleocommunity results of each of the three higher taxonomic levels (family, order, and class) to the genus-level result. High goodness-of-fit statistics (using three different statistical comparison methods) resulted between comparisons of genus- and family-level taxonomic identifications for 28 paleocommunity datasets. However, 15 of the 28 genus- and family-level taxonomic identification comparisons were determined to produce different paleocommunity results based on qualitative-visual comparisons. Thus, family-level identification of specimens may often lead to the same paleocommunity conclusions as genus-level identification; however, inconsistencies generate enough uncertainty that paleocommunity research would benefit from genus-level identification of specimens. Due to the moderate-to-low goodness-of-fit statistics between genus–order and genus–class comparisons of paleocommunities as well as the clear differences found in the qualitative-visual comparisons, order and class did not reliably reproduce genus-level results. Thus, family-level identifications may be sufficient some of the time for studies employing multivariate statistical methods to compare paleocommunities that would otherwise use the genus level; order- and class-level identifications are probably never sufficient.

The Relationship between Genus Richness and Geographic Area in Late Cretaceous Marine Biotas: Epicontinental Sea versus Open-Ocean-Facing Settings

For present-day biotas, close relationships have been documented between the number of species in a given region and the area of the region. To date, however, there have been only limited studies of these relationships in the geologic record, particularly for ancient marine biotas. The recent development of large-scale marine paleontological databases, in conjunction with enhanced geographical mapping tools, now allow for their investigation. At the same time, there has been renewed interest in comparing the environmental and paleobiological properties of two broad-scale marine settings: epicontinental seas, broad expanses of shallow water covering continental areas, and open-ocean-facing settings, shallow shelves and coastlines that rim ocean basins. Recent studies indicate that spatial distributions of taxa and the kinetics of taxon origination and extinction may have differed in these two settings. Against this backdrop, we analyze regional Genus-Area Relationships (GARs) of Late Cretaceous marine invertebrates in epicontinental sea and open-ocean settings using data from the Paleobiology Database. We present a new method for assessing GARs that is particularly appropriate for fossil data when the geographic distribution of these data is patchy and uneven. Results demonstrate clear relationships between genus richness and area for regions worldwide, but indicate that as area increases, genus richness increases more per unit area in epicontinental seas than in open-ocean settings. This difference implies a greater degree of compositional heterogeneity as a function of geographic area in epicontinental sea settings, a finding that is consistent with the emerging understanding of physical differences in the nature of water masses between the two marine settings.

Vision and the diversification of Phanerozoic marine invertebrates

Identifying biological traits that promote evolutionary success is fundamental for understanding biodiversity dynamics and for assessing the evolutionary response of organisms to global change. We tested the hypothesis that image-forming eyes have contributed to the diversification of taxa in the geological past. Using fossil occurrences in the Paleobiology Database, we analyzed the diversity and evolutionary rates of more than 17,000 Phanerozoic genera of marine invertebrates living on or above the shallow-water seafloor according to their visual capabilities. Analysis of the complete data set shows a peak in the proportional diversity of sighted genera early in the Phanerozoic, and their continuance at a relatively low and stable level after the Ordovician. As an explanation of this pattern we suggest that selection pressure to develop eyes rose in the Cambrian, and that behavioral constraints had a balancing effect thereafter. In contrast to the pooled data, a clade-level study of those subgroups that contain both sighted and blind genera revealed that—in trilobites, all epifaunal bivalves, pectinoid bivalves, gastropods, and echinoderms—sighted genera diversified more strongly than blind genera. This difference is controlled by significantly raised extinction rates of blind genera. These more finely resolved patterns support the hypothesis that good vision is a key trait that promoted preferential diversification.

Multivariate assessment of the required sample size for community paleoecological research

When conducting paleocommunity research, a sample size that is too small may lead to erroneous ecological conclusions, while an increasingly larger sample size will eventually result in diminishing returns. Using 30 datasets from the Paleobiology Database and the literature, I present evidence that the median required sample size for paleocommunity research is 25 to 50 individuals. Each sample within each dataset was randomly subsampled 1000 times to five proportional sizes (50%, 25%, 10%, 5%, 2.5%). Each of the 1000 subsampled datasets created for each proportional sample size was correlated with its corresponding complete dataset using three multivariate methods: the Mantel Test, Pearson's Product Moment Correlations of non-metric multidimensional scaling ordination axis scores, and the Procrustean Randomization Test (PROTEST). For median sample sizes greater than 50 individuals, all Mantel R-statistics are greater than 0.93, Pearson's r-values for NMDS axis-one scores are greater than 0.86, and PROTEST m 2-values are greater than 0.82. Between a median sample size of 25 and 50, the R-statistics, r-values, and m 2-values are relatively plateaued, and then subsequently plummet at median sample sizes less than 25. Thus, the multivariate paleocommunity signal, within each dataset is effectively preserved when all median sample sizes are greater than 25 to 50 individuals.

Regional Environmental Breadth Predicts Geographic Range and Longevity in Fossil Marine Genera

BackgroundGeographic range is a good indicator of extinction susceptibility in fossil marine species and higher taxa. The widely-recognized positive correlation between geographic range and taxonomic duration is typically attributed to either accumulating geographic range with age or an extinction buffering effect, whereby cosmopolitan taxa persist longer because they are reintroduced by dispersal from remote source populations after local extinction. The former hypothesis predicts that all taxa within a region should have equal probabilities of extinction regardless of global distributions while the latter predicts that cosmopolitan genera will have greater survivorship within a region than endemics within the same region. Here we test the assumption that all taxa within a region have equal likelihoods of extinction.Methodology/Principal FindingsWe use North American and European occurrences of marine genera from the Paleobiology Database and the areal extent of marine sedimentary cover in North America to show that endemic and cosmopolitan fossil marine genera have significantly different range-duration relationships and that broad geographic range and longevity are both predicted by regional environmental breadth. Specifically, genera that occur outside of the focal region are significantly longer lived and have larger geographic ranges and environmental breadths within the focal region than do their endemic counterparts, even after controlling for differences in sampling intensity. Analyses of the number of paleoenvironmental zones occupied by endemic and cosmopolitan genera suggest that the number of paleoenvironmental zones occupied is a key factor of geographic range that promotes genus survivorship.Conclusions/SignificanceWide environmental tolerances within a single region predict both broad geographic range and increased longevity in marine genera over evolutionary time. This result provides a specific driving mechanism for the spatial and temporal distributions of marine genera at regional and global scales and is consistent with the niche-breadth hypothesis operating on macroevolutionary timescales.

Stratigraphic distribution of marine fossils in North America

The stratigraphic distribution of fossils reflects a combination of physical and biological factors. Although many studies have addressed the distribution of fossils at a basin scale and within sedimentary sequences spanning 10 4 –10 6 yr, little is known about the distribution of fossils within longer duration sedimentary successions covering broad geographic regions. Here we combine a North American macrostratigraphic database with fossil occurrence data from the Paleobiology Database to quantify the stratigraphic distribution of fossils within hiatus-bound marine sedimentary rock packages that have a mean duration of 10 7 yr. We find that fossil collections and marine genera are, when averaged over all Phanerozoic sedimentary rock packages, more abundant than expected in the top 40% of package durations, and less common than expected in the bottom ∼25%. Generic first and last appearance datums (FADs and LADs) in North America are not randomly distributed among fossil collections. Instead, LADs are more common than expected in the top ∼20% of package durations, whereas FADs are more uniformly distributed. This result is not consistent with an unconformity-related sampling bias, but is indicative of greater congruence in the temporal scales over which genus extinction and regression occur than genus initiation and transgression. These results support the hypothesis that macroevolution, particularly genus extinction, and large-scale patterns of sedimentation share a common set of forcing mechanisms that are related to the formation and destruction of shallow-marine habitats.

Northward shift in faunal diversity: A general pattern of evolution of phanerozoic marine biota

The analysis of two global databases on spatio-temporal distribution of fossil marine animal genera (Sepkoski's compendium and The Paleobiology Database) has revealed the presence of the latitudinal diversity gradient (LDG) in the marine realm throughout the Phanerozoic. Within each time interval, LDG is characterized by two parameters: the latitudinal position of peak diversity and the steepness of monotonous decline of diversity with increasing distance from the zone of the highest diversity. During the Phanerozoic, peak diversity has drifted gradually from the tropics and subtropics of the Southern hemisphere into northern midlatitudes. The shift in peak diversity is not likely to be an artifact of incompleteness of the fossil record or uneven sampling of different regions. The shift proceeded in a stepwise manner, with periods of relatively fast changes separated by longer periods of little or no change. The latitudinal shift in peak diversity was probably due to a combination of several causes: tectonic (northward shift in the latitudinal distribution of continental shelf area), climatic (as demonstrated by the fact that peak diversity tended to occur near equator during the cold epochs and in midlatitudes during the warm epochs), and historical ("evolutionary inertia" of local faunas).

Macrostratigraphy and macroevolution in marine environments: testing the common-cause hypothesis

Abstract Quantitative patterns in the sedimentary rock record predict many different macroevolutionary patterns in the fossil record, but the reasons for this predictability remain uncertain. There are two competing, but non-mutually exclusive, hypotheses: (1) similarities reflect a sampling bias imposed by variable and incomplete sampling of fossils, and (2) similarities reflect environmental perturbations that influence both the patterns of sedimentation and macroevolution (i.e., common-cause). Macrostratigraphy, which is based on the quantitative analysis of hiatus-bound rock packages, permits variation in the rock record to be expressed in terms of rock quantity and, more importantly, spatiotemporal continuity. In combination with spatially-explicit fossil occurrence data in the Paleobiology Database, it is now possible to more rigorously test alternative hypotheses for similarities in the rock and fossil records and to start distinguishing between geologically-controlled sampling bias and the common-cause hypothesis. Here we summarize results from measuring the intersection of Macrostrat and the Paleobiology Database. Our results suggest that patterns in the fossil record are not dominated by large-scale stratigraphic biases. Instead, they suggest that linkages between multiple Earth systems are driving both spatiotemporal patterns of sedimentation and macroevolution.

A ubiquitous ∼62-Myr periodic fluctuation superimposed on general trends in fossil biodiversity. I. Documentation

We use Fourier analysis and related techniques to investigate the question of periodicities in fossil biodiversity. These techniques are able to identify cycles superimposed on the long-term trends of the Phanerozoic. We review prior results and analyze data previously reduced and published. Joint time-series analysis of various reductions of the Sepkoski Data, Paleobiology Database, and Fossil Record 2 indicate the same periodicity in biodiversity of marine animals at 62 Myr. We have not found this periodicity in the terrestrial fossil record. We have found that the signal strength decreases with time because of the accumulation of apparently “resistant” long-lived genera. The existence of a 62-Myr periodicity despite very different treatment of systematic error, particularly sampling-strength biases, in all three major databases strongly argues for its reality in the fossil record.

Impact of outcrop area on estimates of Phanerozoic terrestrial biodiversity trends

Abstract Studies of biodiversity through time have primarily focused on the marine realm which is generally considered to have a more complete record than terrestrial environments. Recently, this assumption has been challenged, and it has been argued that the record of life on land is comparable or even more robust than that of the shallow oceans. Moreover, it has been claimed that terrestrial successions preserve an exponential rise in diversity, even when corrected for sampling biases such as changes in continental rock volume through time. We evaluate relations between terrestrial diversity and exposed areas of terrestrial sediments using our compiled data on areas of global continental outcrops and generic diversity from the Paleobiology Database. Terrestrial global generic diversity and terrestrial outcrop area are highly correlated following a linear relation. No significant correlation is observed between habitat area and either outcrop area or biodiversity, suggesting that the observed relation between diversity and outcrop area is not driven by a common cause, such as eustasy. We do find evidence for a small residual increase in diversity through time after removing the effect of outcrop area, but caution that this may be driven by an increased proportion of terrestrial fauna with high preservation potential.

Changes in shell durability of common marine taxa through the Phanerozoic: evidence for biological rather than taphonomic drivers

Phanerozoic trends in shell and life habit traits linked to postmortem durability were evaluated for the most common fossil brachiopod, gastropod, and bivalve genera in order to test for changes in taphonomic bias. Using the Paleobiology Database, we tabulated occurrence frequencies of genera for 48 intervals of ∼11 Myr duration. The most frequently occurring genera, cumulatively representing 40% of occurrences in each time bin, were scored for intrinsic durability on the basis of shell size, reinforcement (ribs, folds, and spines), life habit, and mineralogy.Shell durability is positively correlated with the number of genera in a time bin, but durability traits exhibit different temporal patterns across higher taxa, with notable offsets in the timing of changes in these traits. We find no evidence for temporal decreases in durability that would indicate taphonomic bias at the Phanerozoic scale among commonly occurring genera. Also, all three groups show a remarkable stability in mean shell size through the Phanerozoic, an unlikely pattern if strong size-filtering taphonomic megabiases were affecting the fossil record of shelly faunas. Moreover, small shell sizes are attained in the early Paleozoic in brachiopods and in the latest Paleozoic in gastropods but are steady in bivalves; unreinforced shells are common to all groups across the entire Phanerozoic; organophosphatic and aragonitic shells dominate only the oldest and youngest time bins; and microstructures having high organic content are most common in the oldest time bins.In most cases, the timing of changes in durability-related traits is inconsistent with a late Mesozoic Marine Revolution. The post-Paleozoic increase in mean gastropod reinforcement occurs in the early Triassic, suggesting either an earlier appearance and expansion of durophagous predators or other drivers. Increases in shell durability hypothesized to be the result of increased predation in the late Mesozoic are not evident in the common genera examined here. Infaunal life habit does increase in the late Mesozoic, but it does not become more common than levels already attained during the Paleozoic, and only among bivalves does the elevated late Mesozoic level persist through the Holocene.These temporal patterns suggest control on the occurrence of durability-related traits by individual evolutionary histories rather than taphonomic megabiases. Our findings do not mean taphonomic biases are absent from the fossil record, but rather that their effects apparently have had littleneteffect on the relative occurrence of shell traits generally thought to confer higher preservation potential over long time scales.

Geographical, environmental and intrinsic biotic controls on Phanerozoic marine diversification

Abstract: The Paleobiology Database now includes enough data on fossil collections to produce useful time series of geographical and environmental variables in addition to a robust global Phanerozoic marine diversity curve. The curve is produced by a new ‘shareholder quorum’ method of sampling standardization that removes biases but avoids overcompensating for them by imposing entirely uniform data quotas. It involves drawing fossil collections until the taxa that have been sampled at least once (the ‘shareholders’) have a summed total of frequencies (i.e. coverage) that meets a target (the ‘quorum’). Coverage of each interval’s entire data set is estimated prior to subsampling using a variant of a standard index, Good’s u. This variant employs counts of occurrences of taxa described in only one publication instead of taxa found in only one collection. Each taxon’s frequency within an interval is multiplied by the interval’s index value, which limits the maximum possible sampling level and thereby creates the need for subsampling. Analyses focus on a global diversity curve and curves for northern, southern and ‘tropical’ (30°N to 30°S) palaeolatitudinal belts. Tropical genus richness is remarkably static, so most large shifts in the curve reflect trends at higher latitudes. Changes in diversity are analysed as a function of standing diversity; the number, spacing and palaeolatitudinal position of sampled geographical cells; the mean onshore–offshore position of cells; and proportions of cells from carbonate, onshore and reefal environments. Redundancy among the variables is eliminated by performing a principal components analysis of each data set and using the axis scores in multiple regressions. The key factors are standing diversity and the dominance of onshore environments such as reefs. These factors combine to produce logistic growth patterns with slowly changing equilibrium values. There is no evidence of unregulated exponential growth across any long stretch of the Phanerozoic, and in particular there was no large Cenozoic radiation beyond the Eocene. The end-Ordovician, Permo–Triassic and Cretaceous–Palaeogene mass extinctions had relatively short-term albeit severe effects. However, reef collapse was involved in these events and also may have caused large, longer term global diversity decreases in the mid-Devonian and across the Triassic/Jurassic boundary. Conversely, the expansion of reef ecosystems may explain newly recognized major radiations in the mid-Permian and mid-Jurassic. Reef ecosystems are particularly vulnerable to current environmental disturbances such as ocean acidification, and their decimation might prolong the recovery from today’s mass extinction by millions or even tens of millions of years.