Strata of the Ediacaran Period (635–538.8 Ma) yield the oldest known fossils of complex, macroscopic organisms in the geologic record. These “Ediacaran-type” macrofossils (known as the Ediacaran biota) first appear in mid-Ediacaran strata, experience an apparent decline through the terminal Ediacaran, and directly precede the Cambrian (538.8–485.4 Ma) radiation of animals. Existing hypotheses for the origin and demise of the Ediacaran biota include: changing oceanic redox states, biotic replacement by succeeding Cambrian-type fauna, and mass extinction driven by environmental change. Few studies frame trends in Ediacaran and Cambrian macroevolution from the perspective of the sedimentary rock record, despite well-documented Phanerozoic covariation of macroevolutionary patterns and sedimentary rock quantity. Here we present a quantitative analysis of North American Ediacaran–Cambrian rock and fossil records from Macrostrat and the Paleobiology Database. Marine sedimentary rock quantity increases nearly monotonically and by more than a factor of five from the latest Ediacaran to the late Cambrian. Ediacaran–Cambrian fossil quantities exhibit a comparable trajectory and have strong (rs > 0.8) positive correlations with marine sedimentary area and volume flux at multiple temporal resolutions. Even so, Ediacaran fossil quantities are dramatically reduced in comparison to the Cambrian when normalized by the quantity of preserved marine rock. Although aspects of these results are consistent with the expectations of a simple fossil preservation–induced sampling bias, together they suggest that transgression–regression and a large expansion of marine shelf environments coincided with the diversification of animals during a dramatic transition that is starkly evident in both the sedimentary rock and fossil records.

Geographically explicit, taxonomically resolved fossil occurrences are necessary for reconstructing macroevolutionary patterns and for testing a wide range of hypotheses in the Earth and life sciences. Heterogeneity in the spatial and temporal distribution of fossil occurrences in the Paleobiology Database (PBDB) is attributable to several different factors, including turnover among biological communities, socioeconomic disparities in the intensity of paleontological research, and geological controls on the distribution and fossil yield of sedimentary deposits. Here we use the intersection of global geological map data from Macrostrat and fossil collections in the PBDB to assess the extent to which the potentially fossil-bearing, surface-expressed sedimentary record has yielded fossil occurrences. We find a significant and moderately strong positive correlation between geological map area and the number of fossil occurrences. This correlation is consistent regardless of map unit age and binning protocol, except at period level; the Neogene and Quaternary have non-marine map units covering large areas and yielding fewer occurrences than expected. The sedimentary record of North America and Europe yields significantly more fossil occurrences per sedimentary area than similarly aged deposits in most of the rest of the world. However, geographic differences in area and age of sedimentary deposits lead to regionally different expectations for fossil occurrences. Using the sampling of surface-expressed sedimentary units in North America and Europe as a predictor for what might be recoverable from the surface-expressed sedimentary deposits of other regions, we find that the rest of the globe is approximately 45% as well sampled in the PBDB. Using age and area of bedrock and sampling in North America and Europe as a basis for prediction, we estimate that more than 639,000 occurrences from outside these regions would need to be added to the PBDB to achieve global geological parity in sampling. In general, new terrestrial fossil occurrences are expected to have the greatest impact on our understanding of macroevolutionary patterns.

Ammonites have disparate adult morphologies indicative of diverse ecological niches, but ammonite hatchlings are small (~1 mm diameter), which raises questions about the similarity of egg incubation and hatchling life mode in ammonites. Modern Nautilus is sometimes used as a model organism for understanding ammonites, but despite their outward similarities, the groups are only distantly related. Trends in ammonite diversity and extinction vulnerability in the fossil record contrast starkly with those of nautilids, and embryonic shells from Late Cretaceous ammonites are two orders of magnitude smaller than nautilid embryonic shells. To investigate possible environmental changes experienced by ammonite hatchlings, we used secondary ion mass spectrometry to analyze the oxygen and carbon isotope composition of the embryonic shells and early postembryonic whorls of five juveniles of Hoploscaphites comprimus obtained from a single concretion in the Fox Hills Formation of South Dakota. Co-occurring bivalves and diagenetic calcite were also analyzed to provide a benthic baseline for comparison. The oxygen isotope ratios of embryonic shells are more like those of benthic bivalves, suggesting that ammonite eggs were laid on the bottom. Ammonite shell immediately after hatching has more negative δ18O, suggesting movement to more shallow water that is potentially warmer and/or fresher. After approximately one whorl of postembryonic growth, the values of δ18O become more positive in three of the five individuals, suggesting that these animals transitioned to a more demersal mode of life. Two other individuals transition to even lower δ18O values that could suggest movement to nearshore brackish water. These data suggest that ammonites, like many modern coleoids, may have spawned at different times of the year. Because scaphites were one of the short-term Cretaceous–Paleogene extinction survivors, it is possible that this characteristic allowed them to develop a broader geographic range and, consequently, a greater resistance to extinction.

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.

A growing body of work has quantitatively linked many macroevolutionary patterns, including short- and long-term changes in biodiversity, rates of taxonomic extinction and origination, and patterns of extinction selectivity, to temporal variability in the sedimentary rock record. Here we establish a new framework for more rigorously testing alternative hypotheses for these and many other results by documenting the large-scale spatiotemporal intersection of the North American sedimentary rock and fossil records. To do this, we combined 30,387 fossil collections in the spatially explicit Paleobiology Database with a comprehensive macrostratigraphic database consisting of 18,815 sedimentary lithostratigraphic units compiled from 814 geographic regions distributed across the United States and Canada. The geological completeness of paleontological sampling, here defined as the proportion of the available sedimentary rock record that has been documented to have at least one fossil occurrence, irrespective of taxonomy or environment, is measured at four different levels of stratigraphic resolution: (1) lithostratigraphic rock units, (2) hiatus-bound rock packages, (3) regional stratigraphic columns, and (4) sediment coverage area (km2). Mean completeness estimates for 86 Phanerozoic time intervals (approximately stages; median duration 5.3 Myr) range from 0.18 per interval in the case of lithostratigraphic rock units to 0.23 per interval for stratigraphic columns and sediment coverage area. Completeness estimates at all four levels of stratigraphic resolution exhibit similar temporal variation, including a significant long-term increase during the Phanerozoic that is accentuated by an abrupt Campanian–Maastrichtian peak. This Late Cretaceous peak in completeness is approximately five times greater than the least complete Phanerozoic time intervals (Early Cambrian, Early Devonian, late Permian, and Early Cretaceous). Geological completeness in the Cenozoic is, on average, approximately 40% greater than in the Paleozoic. Temporal patterns of geological completeness do not appear to be controlled exclusively by variation in the frequency of subsurface rock units or an increase over time in the proportion of terrestrial rock, but instead may be general features of both the marine and terrestrial fossil records.

Much of what is known about the long-term history of biodiversity and rates of taxonomic evolution in the fossil record derives from literature-based compilations of fossil stratigraphic ranges. It has been suggested that taxonomic and stratigraphic errors in these compilations are randomly distributed and, therefore, introduce no significant bias to macroevolutionary patterns. Here we compare a new, comprehensive global database of Ordovician and Early Silurian crinoids to Sepkoski's global genus compendium.

Approximately 44% of the crinoid genera resolved to substage in Sepkoski's compendium are taxonomically inaccurate (i.e., invalid, nomina dubia, or column genera) or have incorrect first and/or last occurrences. Errors in Sepkoski's compendium result from incomplete coverage of existing taxonomic work and incorrect stratigraphic correlations that, in some cases, are propagated throughout the taxonomic literature. Stratigraphic range errors are nonrandomly distributed among substages in Sepkoski's compendium. The result is underestimated richness in the Early Silurian and significantly overestimated rates of extinction in the Late Ordovician. There is no similar bias in Sepkoski's substage origination rates for crinoids.

At the stage-level of temporal resolution, Sepkoski's crinoid data are more accurate. In this case, only 32% of the compendium's crinoid genera contain some stratigraphic or taxonomic inaccuracy. However, errors still result in incorrect macroevolutionary patterns, particularly with respect to rate of origination in the Ashgill, which is significantly underestimated in Sepkoski's compendium. Genera described since the completion of Sepkoski's compendium have had relatively little effect on estimated rates of evolution at both stage and substage resolution.

These results suggest that macroevolutionary patterns among some taxa in Sepkoski's compilation may be significantly influenced by nonrandomly distributed taxonomic inaccuracies and stratigraphic range errors. In the case of the apparent end-Ordovician mass extinction among crinoids, the revised history reveals a dramatically reduced role for extinction at the substage-level of temporal resolution. At the stage level, Sepkoski's original compilation strongly exaggerates the excess of extinction over origination in the Ashgill. Although biases inherent in the stratigraphic record remain unaccounted for, removing taxonomic and stratigraphic errors in Sepkoski's compendium substantially changes our understanding of the nature of large-scale biotic change for an important Paleozoic taxon during the end-Ordovician.

Temporal variation in sampling intensity and geologically controlled rates of fossil preservation distort macroevolutionary patterns in the fossil record. Here, we use a comprehensive, list-based compilation of taxonomically and stratigraphically vetted global crinoid genus occurrences to evaluate and correct for the effects of variable and incomplete sampling from the Ordovician through Early Silurian. After standardizing the number of occurrences or the number of biofacies used to estimate the stratigraphic ranges of genera and after adjusting rates of turnover to account for the incomplete preservation of true extinction and origination pulses, we find support for several important revisions to the macroevolutionary history of crinoids. First, in contrast to the uncorrected data, sample-standardized genus richness does not appear to increase by more than 20% after an abrupt Middle Ordovician (Harnagian) diversification. Second, the only significant short-term change in genus richness following the Harnagian increase is a ≥24% decline from the Rawtheyan to the Hirnantian. Third, volatility in rates of genus extinction is increased after adjusting for preservation and there remain significant peaks of extinction in the Rawtheyan, which marks the end-Ordovician extinction, and in the middle of the Early Silurian. Finally, significant increases in origination rates occur in the Early Silurian. These results reaffirm the importance of the end-Ordovician extinction for crinoids, but they also highlight the comparatively poorly sampled Early Silurian as a time of turnover among crinoids.

Crinoid genus extinction rates are positively correlated with area-weighted rates of sedimentary package truncation, suggesting that extinction may have been controlled by physical environmental changes, such as the contraction of unique epicontinental sea habitats. The lack of a correlation between genus origination and sedimentary package initiation reinforces this hypothesis and suggests that other factors, such as evolutionary innovations and biotic interactions during the Ordovician radiation, may have been more important in controlling the diversification of crinoids.

The relative proportions of Sepkoski's Cambrian, Paleozoic, and Modern evolutionary faunas in Cambrian-Ordovician benthic marine assemblages from mixed carbonate-shale and shale lithofacies deposited below normal wave base (herein, deep subtidal) in North America are strongly positively correlated with global relative genus richness in Sepkoski's global compendium. The correlation between local and global faunal proportions is robust regardless of how proportions are calculated, including when local proportions are based on number of specimens. Like the global pattern, the transition between the Cambrian and Paleozoic evolutionary faunas appears to occur gradually, in that Lower Arenigian (Ibexian) deep subtidal assemblages contain approximately equal proportions of Cambrian and Paleozoic faunal elements. In agreement with previous work, an onshore-offshore differentiation of faunas is evident both within Ordovician deep subtidal communities and across a larger environmental gradient.

Within the deep subtidal assemblages studied here, the Paleozoic fauna tends to have a greater proportion of individuals for a given proportion of genera than the Cambrian fauna, although both tend to accrue genera at similar rates with increasing relative abundance. The Modern evolutionary fauna appears to accrue genera more rapidly with increasing local relative abundance. The extent to which these differences reflect ecological factors such as biomass, metabolic requirements or larval recruitment patterns, taxonomic practices stemming from variable morphospace saturation, or taphonomy-related counting biases remains unclear, but it suggests the possibility that Sepkoski's evolutionary faunas may share ecological characteristics that influence both local relative abundance and global rates of taxonomic evolution.

Short-term variations in rates of taxonomic extinction and origination in the fossil record may be the result of true changes in rates of turnover, variable rates of fossil preservation, or some combination of the two. Here, positive extinction and origination rate excursions among Phanerozoic marine animal genera are reexpressed in terms of the amount of normal, background time they represent. In addition to providing a background-adjusted calibration of rate intensities, this reexpression determines the durations of sampling gaps that would be required to explain entirely all observed rate excursions as sampling artifacts. This possibility is explored by analyzing a new compilation of the timing and duration of sedimentary hiatuses in North America.

Hiatuses spanning more than approximately one million years (Myr) in the marine sedimentary rock record have a mean duration of 73 Myr. There are two major hiatus types—those that form in response to long-duration tectonic cycles and that bound the major Sloss-scale sequences (mean duration 200 Myr), and those that form in response to shorter-duration changes in sediment accommodation space and that occur within major Sloss-scale sequences (mean duration less than 23 Myr). The latter are approximately exponentially distributed and have a mean duration that is comparable to the mean duration of intervening sedimentary rock packages.

Although sedimentary hiatuses are generally long enough in duration to accommodate the hypothesis that short-term variations in rates of genus origination and extinction are artifacts of sampling failures at major unconformities (“Unconformity Bias” hypothesis), the observed evolutionary rates are not correlated with hiatus durations. Moreover, hiatuses that follow the major mass extinctions are not long in comparison to most other non-mass extinction intervals. These results do not support the hypothesis that hiatuses at major unconformities alone have artificially clustered genus first and last occurrences, thereby causing many of the documented statistical similarities between the temporal structure of the sedimentary rock record and macroevolutionary patterns. Instead, environmental changes related to the expansion and contraction of marine environments may have been the primary forcers of both biological turnover and the spatio-temporal pattern of sediment accumulation. Fully testing this “Common Cause” hypothesis requires quantifying and overcoming lingering taxonomic, biostratigraphic, facies, and numerous other biases that are both inherent in geologic data and imposed by imperfect knowledge of the fossil record.

Biodiversity has two principal components: richness (the number of taxa) and evenness (the distribution of individuals among taxa). Both of these attributes are critical in defining community composition and structure, but evenness may be particularly important for ecological reasons, especially in the context of a possible evolutionary increase in richness. Here I examine abundance data in well-preserved Cambrian and Ordovician benthic marine assemblages from mixed carbonate-shale and shale lithofacies deposited below normal wave base in North America. Evenness increases significantly from the Cambrian to the Ordovician in these assemblage data. The increase cannot easily be attributed to differences in sample size, lithology, water depth, or other sample characteristics. There is relatively little variation in evenness among stages within the Cambrian and Ordovician periods. Much of the within-period variance in evenness appears to arise from environmental and / or taphonomic differences that may exist between stratigraphic formations, but some variance may also be ascribed to the degree of taxonomic and / or ecological overlap among dominant taxa. Specifically, assemblages that are co-dominated by taxa from the same class or order tend to have lower evenness than assemblages dominated by genera from different higher taxa, but the effect is not strong in these data.

The Cambrian and Paleozoic evolutionary faunas show similar, but out-of-phase, patterns of evenness within assemblages. Both faunas have comparably low evenness early in their history but then increase to similar, higher evenness values. In the case of the Cambrian fauna, the increase occurs in the Late Cambrian or Early Ordovician. In the Paleozoic fauna, the increase appears to occur after the lower Arenigian.

The Paleobiology Database (PBDB; https://paleobiodb.org) consists of geographically and temporally explicit, taxonomically identified fossil occurrence data. The taxonomy utilized by the PBDB is not static, but is instead dynamically generated using an algorithm applied to separately managed taxonomic authority and opinion data. The PBDB owes its existence to many individuals, some of whom have entered more than 1.26 million fossil occurrences and over 570,000 taxonomic opinions, and some of whom have developed and maintained supporting infrastructure and analysis tools. Here, we provide an overview of the data model currently used by the PBDB and then briefly describe how this model is exposed via an Application Programming Interface (API). Our objective is to outline how PBDB data can now be accessed within individual scientific workflows, used to develop independently managed educational and scientific applications, and accessed to forge dynamic, near real-time connections to other data resources.

Superbly preserved specimens of Eucalyptocrinites tuberculatus from the Waldron Shale (Silurian, Wenlockian) of Indiana have been found with epibionts attached in living position to their stems. The rhynchonellid brachiopod Stegerhynchus indianense, the tabulate coral Favosites forbesi, the annelids? Spirorbis and Cornulites, bryozoans, and rarely the ichnogenus Tremichnus utilized living crinoids as secondary tiering surfaces. Crinozoans also attached to upright crinoid columns, and their holdfasts are the most abundant epibionts on pluricolumnals. Eucalyptocrinites crassus individuals contributed to the success of their epibionts by providing stable attachment surfaces elevated up to one meter above the sediment-water interface. Although crinoid-epibiont relationships are frequently blurred by taphonomic processes, articulated crinoid specimens and encrusters on pluricolumnals suggest that secondary tiering was a significant paleoecological element in the Waldron Shale.

Unfossiliferous marine sedimentary rocks of Phanerozoic age are known to all field-oriented paleontologists. These troublesome units are often encountered in the field, perhaps cursed roundly for a moment or two, and usually shrugged off in pursuit of the next fossiliferous interval. Paleontologists tend not to discuss barren units, and they rarely publish on the absence of a fauna from what appears to be unaltered marine rock. But aren't barren marine sediments revealing something important about their paleoenvironment and possibly about the paleoenvironments of conformably adjacent fossil-bearing units? Shouldn't paleontologists be just as interested in knowing the locations and ages of unfossiliferous sediments as they are fossiliferous strata?

Macrostratigraphy is the study and statistical analysis of sediment packages that formed continuously at a specified scale of temporal resolution and that are bound by gaps recognizable at that same scale. The temporal ranges of gap-bound packages, compiled separately for different geographic locations, permit area-weighted, survivorship-based measures of rock quantity and spatio-temporal environmental continuity to be measured. Analytical basin fill models suggest that the parameters controlling sedimentation and sequence stratigraphic architecture, such as base level and sediment supply, can be detected quantitatively by macrostratigraphy.

Macrostratigraphic analysis of the marine sedimentary rock record in the United States at a temporal resolution of ~106 years reproduces most of the well-known Sloss sequences, but it also identifies two prominent megasequences, the Paleozoic and Modern megasequences, which are separated by a Permian-Triassic discontinuity and Phanerozoic minimum in rock quantity. Many short- and long-term features of the macroevolutionary history of marine animals are reproduced by macrostratigraphy, including 1) many patterns in genus richness, 2) patterns in rates of genus extinction and, to a lesser degree, rates of origination, and 3) patterns of extinction selectivity and the shifting relative richness of Sepkoski's Paleozoic and Modern evolutionary faunas. The extent to which macrostratigraphy reproduces the macroevolutionary history of marine animals transcends what is expected by geologically-controlled sampling biases. Instead, the processes which control the spatio-temporal dynamics of shelf sedimentation, including expansions and contractions of shallow epicontinental seas, have probably exerted a consistent influence on the macroevolutionary history of marine animals. Exploring the common cause hypothesis by putting fossils back into rocks and rocks into a new quantitative framework for physical environmental change holds considerable promise for paleobiology.