Researchers often use large databases to conduct their studies; however, they do not always provide credit, through citations, to the people who produced the data in the databases. In the field of paleontology, researchers use a large database called the Paleobiology Database (PBDB) to study global patterns and processes over millions of years. These studies use data from the PBDB and typically receive a greater number of citations than the original data-producing papers. This creates a situation where the hard work of collecting the data is not credited and rewarded in a fair way, even though this work is equally important to the field of paleontology. By fixing this issue and giving proper credit to data-producing papers, paleontology itself can be strengthened by increasing the incentives for producing data and at the same time creating more high-quality data for everyone to use.

Data compilations expand the scope of research; however, data citation practice lags behind advances in data use. It remains uncommon for data users to credit data producers in professionally meaningful ways. In paleontology, databases like the Paleobiology Database (PBDB) enable assessment of patterns and processes spanning millions of years, up to global scale. The status quo for data citation creates an imbalance wherein publications drawing data from the PBDB receive significantly more citations (median: 4.3 ± 3.5 citations/year) than the publications producing the data (1.4 ± 1.3 citations/year). By accounting for data reuse where citations were neglected, the projected citation rate for data-provisioning publications approached parity (4.2 ± 2.2 citations/year) and the impact factor of paleontological journals (n = 55) increased by an average of 13.4% (maximum increase = 57.8%) in 2019. Without rebalancing the distribution of scientific credit, emerging “big data” research in paleontology—and science in general—is at risk of undercutting itself through a systematic devaluation of the work that is foundational to the discipline.

The fossil record is notoriously incomplete. The spatial distribution of fossils reflects in part the geography of biodiversity gradients, areas of sediment deposition and present-day rock exposure, and locations of wealthy nations with long-standing investments in Western science. Importantly for paleobiologists, the geographic location and size of fossil sampling gaps varies through time, between environments, and from one group of organisms to another. This spatial structure in recorded fossil occurrences has many consequences for ecological and evolutionary investigations. If the fossil record is taken at face value, results and conclusions will be inaccurate, sometimes to the point of being misleading. Therefore, it is essential to standardize the spatial distribution of fossil occurrences (the total area covered by sites and the spread across sites) before addressing research questions about diversity dynamics, geographic range size, or other ecological variables. We review sources of spatial structure in the fossil record, means to account for them, and possible consequences of leaving them unaddressed. Several of the tools we discuss are compiled into a new software package named divvy, in the R language of data analysis. We call for the paleobiology community to take up spatial standardization as a routine consideration in studying the informative but patchy fossil record.

The fossil record is spatiotemporally heterogeneous: taxon occurrence data have patchy spatial distributions, and this patchiness varies through time. Large-scale quantitative paleobiology studies that fail to account for heterogeneous sampling coverage will generate uninformative inferences at best and confidently draw wrong conclusions at worst. Explicitly spatial methods of standardization are necessary for analyses of large-scale fossil datasets, because nonspatial sample standardization, such as diversity rarefaction, is insufficient to reduce the signal of varying spatial coverage through time or between environments and clades. Spatial standardization should control both geographic area and dispersion (spread) of fossil localities. In addition to standardizing the spatial distribution of data, other factors may be standardized, including environmental heterogeneity or the number of publications or field collecting units that report taxon occurrences. Using a case study of published global Paleobiology Database occurrences, we demonstrate strong signals of sampling; without spatial standardization, these sampling signatures could be misattributed to biological processes. We discuss practical issues of implementing spatial standardization via subsampling and present the new R package divvy to improve the accessibility of spatial analysis. The software provides three spatial subsampling approaches, as well as related tools to quantify spatial coverage. After reviewing the theory, practice, and history of equalizing spatial coverage between data comparison groups, we outline priority areas to improve related data collection, analysis, and reporting practices in paleobiology.

Evolution works through the interaction of ecology and genealogy in time and space. Ecological hierarchy describes processes of energy and matter transfer, while genealogical hierarchy describes patterns of genetic heritability at many scales. Here a new and hybrid in nature, eco-genealogical Bretskyan hierarchy is described. Basic units of this hierarchy are spatially and temporally distinct portions of biota. Proximity of organisms and taxa in space and time enables their coevolution and integration. Lower tiers of this hierarchy are occupied by holobionts—organism-like communities; while at higher tiers, this hierarchy occupied by what are called here geobiomes—local and regional biotas and embedding geosystems that evolve in tandem and exist on geological time scales. The largest rank in the Bretskyan hierarchy is the global biota—Gaia herself. Geobiomes described here are evolutionary individuals with beginnings and ends and defined spatial ranges. The individuality of geobiomes is defined by geological barriers. Barriers form at all time and space scales, and because larger barriers last longer, geobiomes are more individuated at larger spatial scales. The structure of a planet is imposed on biota. Here we present a theoretical framework on how we should understand this geologically imposed structuring, which determines the spatial extents and durations of coevolution and integration and disintegration of biotas, as well as their transformation in time and space.

The process of evolution and the structures it produces are best understood in the light of hierarchy theory. The biota traditionally is described by either the genealogical Linnaean hierarchy or economic hierarchies of communities or ecosystems. Here we describe the Bretskyan hierarchy—a hybrid eco-genealogical hierarchy that consists of nested sets of different-sized, usually polyphyletic communities of interacting individuals separated from other such communities in space and time at multiple scales. The Bretskyan hierarchy consists of elements that have both genealogical and economic properties and functions—situated between, and connecting the elements of, the economic hierarchies (Vernadskyan) and the genealogical (Linnaean) hierarchy. The described hierarchy at lower tiers is populated by holobionts, individuals composed of multiple polyphyletic lineages integrated by functional interactions or biotically fabricated structures, such as membranes. At larger spatial tiers and longer time scales, the members of the Bretskyan hierarchy are of a more diffuse nature, partially due to the small size and relatively short duration of us as observers of larger and longer-lasting structures, here described as geobiomes. Their individuality is externally forced and directly tied to the spatial and temporal physical structures of our planet. These are sub-bioprovinces and bioprovinces—large and effectively isolated spatiotemporal structures of biota integrated internally by coevolution and individuated externally by a hierarchy of barriers. Gaia is here understood as the largest eco-genealogical individual compartmentalized by the outer space of the Earth and integrated at long time scales by biotic interactions and plate tectonic mixing of biota. The existence of a hierarchy of barriers and multilevel allopatry suggests that geographic isolation takes part not only in individuating species lineages, but also in producing coherent complexes of separate lineages forming bioprovinces at multiple space and time scales. The sizes, configurations, and durations of Bretskyan units are directly tied to geodynamics, demonstrating the central role of the physical planet in the processes of individuation and merging of geobiomes and the control of coevolution, and all its ramifications, at multiple space and time scales. The Bretskyan hierarchy also allows the integration of previously unconnected themes—“egalitarian” major transitions in individuality (e.g., eukaryogenesis) and some of the megatrajectories in the history of life—into a single theoretical framework of spatial and temporal scaling of eco-genealogy. The pervasive scaling of geodynamical processes and the direct connection of geodynamics to the dynamics of Bretskyan units allows us to formulate conjectures on the scales and limits of spatial and temporal contingency and competitiveness of biotas in evolution.

Paleontologists have long struggled to compare fossil biodiversity to the biodiversity we see around us. Yet such comparisons are crucial as we attempt to understand and divert an approaching wave of extinction. Here, we bridge the gap between modern and fossil biodiversity by modeling modern tetrapods as fossils, known only from remains preserved in sedimentary rocks. As the first global model of fossilization potential, this provides a profound and previously unavailable perspective. We find that geography strongly structures fossil diversity, producing deeply heterogeneous preservation rates in different tetrapod groups, and, for the globally threatened amphibians, massively underrepresenting extinction. Our results elucidate how physiological and ecological traits of animals influence our ability to recover the history of life.

We know the fossil record is incomplete, but just how much biodiversity does it miss? We produce the first geographically controlled estimate by comparing the geographic ranges of 34,266 modern tetrapods with a map of the world's sedimentary basins. By modeling which tetrapods live within sedimentary basins, we produce a first-order estimate of what might be found in the fossil record of the future. In this record, nearly 30% of tetrapod species have almost no chance of fossilizing, and more stringent criteria for fossilization exclude far more diversity. This geographically structured fossil record preserves disparate patterns of taxonomic and phylogenetic diversity in different tetrapod groups and underpreserves projected extinctions. For the globally threatened amphibians, the magnitude of the extinction of all endangered species would be underestimated by 66–98% in our future record. These results raise profound questions about the structure of the fossil record. Is it capable of recording major origination and extinction events on land? Have swaths of terrestrial diversity gone unrecorded based on geography alone? There are chapters of Earth history that paleontologists can never hope to know, but what is missing, and why?

The Fezouata Shale Formation in present-day Morocco is a site of exceptional fossil preservation from the Lower Ordovician that provides a unique view of animal life before one of the most important radiation events in Earth's history, the great Ordovician biodiversification event (GOBE). Previous work on the fossil diversity of the Fezouata Shale has suggested that there are faunistic differences between the two major intervals with exceptional preservation and that the overall shelly biota of the Fezouata Shale is comparable to other Lower Ordovician sites that reflect open-marine conditions. In this study, we make the first comprehensive quantitative comparison between the Fezouata Shale Formation and other high-latitude Early Ordovician sites based on their shelly fossil biotas with publicly available fossil occurrence information from the Paleobiology Database. We find that the fossil subassemblages of the stratigraphically older lower Fezouata Shale are more heterogeneous than those of the younger upper Fezouata Shale. The fossil biota preserved in the lower Fezouata Shale is most similar to those found in other high-latitude deposits from the Lower Ordovician. We also find that there are differences in faunal composition between Tremadocian- and Floian-aged deposits. Our work provides the first quantitative support for faunistic differences between the lower and upper Fezouata Shale Formation and indicate that the lower Fezouata Shale conventional fossil biota is typical for the Tremadocian, further contextualizing the ecology of the polar regions before the GOBE as informed by this major site of exceptional fossil preservation.

The Fezouata Shale Formation has dramatically impacted our understanding of Early Ordovician marine ecosystems before the great Ordovician biodiversification event (GOBE), thanks to the abundance and quality of exceptionally preserved animals within it. Systematic work has noted that the shelly fossil subassemblages of the Fezouata Shale biota are typical of open-marine deposits from the Lower Ordovician, but no studies have tested the quantitative validity of this statement. We extracted 491 occurrences of recalcitrant fossil genera from the Paleobiology Database to reconstruct 31 subassemblages to explore the paleoecology of the Fezouata Shale and other contemporary, high-latitude (66°S–90°S) deposits from the Lower Ordovician (485.4–470 Ma) and test the interpretation that the Fezouata Shale biota is typical for an Ordovician open-marine environment. Sørensen's dissimilarity metrics and Wilcoxon tests indicate that the subassemblages of the Tremadocian-aged lower Fezouata Shale are approximately 20% more heterogenous than the Floian-aged upper Fezouata Shale. Dissimilarity metrics and visualization suggest that while the lower Fezouata and upper Fezouata share faunal components, the two sections have distinct faunas. We find that the faunal composition of the lower Fezouata Shale is comparable with other Tremadocian-aged subassemblages from high latitudes, suggesting that it is typical for an Early Ordovician open-marine environment. We also find differences in faunal composition between Tremadocian- and Floian-aged deposits. Our results corroborate previous field-based and qualitative systematic studies that concluded that the shelly assemblages of the Fezouata Shale are comparable with those of other Lower Ordovician deposits from high latitudes. This establishes the first quantitative baseline for examining the composition and variability within the assemblages of the Fezouata Shale and will be key to future studies attempting to discern the degree to which it can inform our understanding of marine ecosystems just before the start of the GOBE.

We measured morphological traits in 112 specimens of the Late Cretaceous ammonoid genus Placenticeras from Alabama (USA). Previous studies of Placenticeras have found evidence of morphological differences between juveniles and adults and between the two sexes, differences that were not considered in the designation of taxon names, suggesting this genus is oversplit. We used linear mixed models to describe how specimen shape scales with specimen size, to evaluate individual variation in growth (exploiting repeated measurements from individual specimens), and to assess changes in specimen shape through time. Using a population approach to defining species names (as opposed to the traditional approach, which relies on a “type” specimen), we disregarded existing assigned species names and used principal component analysis and clustering analysis to evaluate how many distinct groups emerge from the morphological data.

We found strong support for at least two distinct clusters of Placenticeras specimens in multivariate morphological space, consistent with two sexes. The sexes separated mainly by size, and secondarily by shape. Further division of adult individuals was not supported, challenging the validity of most existing species names. We observed changes in specimen shape through time, though these changes did not create distinct morphological groups. Two successive species may exist, and Placenticeras may have some use for coarse biostratigraphy in this region. Individuals previously assigned the genus names Stantonoceras or Placenticeras overlapped in shape, indicating the use of these separate genera is not supported. This study demonstrates that the traditional species divisions of Placenticeras should be reevaluated.

A traditional typological approach to taxonomy often does not adequately account for intraspecific variation and can result in taxonomic oversplitting. For many groups, including ammonoids of the Placenticeras genus, intraspecific variation documented in recent studies (e.g., ontogenetic changes, sexual dimorphism, polymorphism) challenges the historic proliferation of species names. Here, we used a population approach to taxonomy and quantitatively evaluated morphometric variation in a sample of Late Cretaceous (Santonian–Campanian) Placenticeras from Alabama and adjacent counties.

We used linear mixed models (LMMs) to characterize how morphological variables scale with conch size across the sample, exploiting mixed longitudinal data to evaluate individual variation in growth and inform interpretations of multivariate analyses. Extended LMMs incorporating geological formation evaluated morphological changes through time. Principal component analysis and clustering analysis were then used to evaluate the number of distinct clusters that emerged in multivariate morphospace independent of previous taxon name assignments.

Discontinuous scaling relationships and distinct clusters in multivariate space suggest sexual dimorphism characterized by differences in adult size and, secondarily, shape. Previous Stantonoceras and Placenticeras assignments broadly overlap in our morphospace, failing to justify this historic distinction (as sexual dimorphs or as genera or subgenera). Placenticeras conch morphology and ornament placement changed through time, suggesting a potential utility for coarse (stage-level) biostratigraphy. However, temporal changes were not associated with distinct clusters in morphospace, and our data fail to support the plethora of reported species names. As few as one or two (successive) species may be present in our sample (representing 130 years of collection effort). In addition to highlighting the need for a significant taxonomic revision of the Placenticeras genus, this study demonstrates the utility of LMMs for distinguishing between different sources of morphological variation, improving interpretations of morphospace under a population approach to taxonomy, and maximizing the amount of ontogenetic information that can be obtained nondestructively.

Chondrichthyans (cartilaginous fishes, including sharks, rays, skates, and chimaeras) first appeared more than 450 million years ago in the Ordovician and diversified into many of the groups that still exist today. However, their biodiversity patterns across the rest of the Paleozoic (Silurian–Permian) are obscured by gaps in their fossil record, caused by several biases. For example, chondrichthyan skeletons are predominantly made of cartilage, which rarely fossilizes, therefore limiting the quality of their fossil record. In our study, we use a newly created dataset of chondrichthyan fossil occurrences and apply statistical methods that aim to estimate patterns of diversity from incomplete fossil samples. Through this approach, we found that chondrichthyan diversity was initially low in the Ordovician and Silurian, then increased substantially in the Early Devonian, about halfway through the Paleozoic. Diversity peaked in the middle Carboniferous before decreasing across the remainder of the Paleozoic. This peak in diversity is dominated by stem-holocephalan chondrichthyans (a major group of Paleozoic chondrichthyans). Conversely, acanthodian chondrichthyan (early shark-like fish) diversity is highest in the Early Devonian before declining rapidly by the end of the Devonian. This suggests that there were two radiations in chondrichthyan diversity during the Paleozoic: the first in the earliest Devonian, led by acanthodian chondrichthyans, and the second in the earliest Carboniferous, led by holocephalans. Early in the Paleozoic, chondrichthyans lived in shallower waters, but after the Devonian, they increasingly branched out into deeper waters. This transition coincides with the Hangenberg extinction event at the end of the Devonian, suggesting that the dispersal of chondrichthyans, specifically holocephalans, into deeper-water environments and expansion of their niches was a response to the impacts of the Hangenberg extinction event on other species in the oceans.

The Paleozoic represents a key time interval in the origins and early diversification of chondrichthyans (cartilaginous fishes), but their diversity and macroevolution are largely obscured by heterogenous spatial and temporal sampling. The predominantly cartilaginous skeletons of chondrichthyans pose an additional limitation on their preservation potential and hence on the quality of their fossil record. Here, we use a newly compiled genus-level dataset and the application of sampling standardization methods to analyze global total-chondrichthyan diversity dynamics through time from their first appearance in the Ordovician through to the end of the Permian. Subsampled estimates of chondrichthyan genus richness were initially low in the Ordovician and Silurian but increased substantially in the Early Devonian. Richness reached its maximum in the middle Carboniferous before dropping across the Carboniferous/ Permian boundary and gradually decreasing throughout the Permian. Sampling is higher in both the Devonian and Carboniferous compared with the Silurian and most of the Permian stages. Shark-like scales from the Ordovician are too limited to allow for some of the subsampling techniques. Our results detect two Paleozoic radiations in chondrichthyan diversity: the first in the earliest Devonian, led by acanthodians (stem-group chondrichthyans), which then decline rapidly by the Late Devonian, and the second in the earliest Carboniferous, led by holocephalans, which increase greatly in richness across the Devonian/ Carboniferous boundary. Dispersal of chondrichthyans, specifically holocephalans, into deeper-water environments may reflect a niche expansion following the faunal displacement in the aftermath of the Hangenberg extinction event at the end of the Devonian.

Crocodylomorpha is a large group of reptiles now restricted to modern crocodilians. Among them, Tethysuchia is a small group of semi-amphibious crocodiles that crossed two biological crises: the second Oceanic Anoxic Event (OAE 2) and the Cretaceous/Paleogene (K/Pg) crisis. Numerous studies have sought to find the driving factors explaining crocodylomorph evolution, producing contradictory conclusions. Studies of smaller groups may help find new exclusive patterns. Here, we studied factors driving tethysuchian evolution using phylogenetically informed statistical analyses. First, we tested whether or not tethysuchian extinction was random across the tips of phylogeny for both crises. Then, we tested the influence of biological (body size, snout proportion) and climatic (temperature, paleolatitude) factors on the evolution of tethysuchian diversity at the OAE 2 and K/Pg crises. Finally, we tested whether temperature influenced the evolution of body size. We conclude that (1) extinction was not random in regard to phylogeny for Tethysuchia at the OAE 2 and K/Pg crises; (2) while an important tethysuchian turnover follows OAE 2, the K/Pg crisis was followed by an explosion in diversity of tethysuchians, which may be explained by the disappearance of marine competitors such as mosasaurs; (3) tethysuchians lived in warmer environments after OAE 2, possibly because of both global warming and changes in latitudinal distribution; (4) there is an ecological diversification after both crises, observable by snout reduction, probably caused by niche partitioning; and (5) there is a positive correlation between body size and temperature, possibly because of a longer growth season.

Crocodylomorpha is a large and diverse clade with a long evolutionary history now restricted to modern crocodilians. Tethysuchia is a less-inclusive clade of semi-amphibious taxa that crossed two biological crises: the second Oceanic Anoxic Event (OAE 2) and the Cretaceous/Paleogene (K/Pg) crisis. Numerous studies have sought to find the driving factors explaining crocodylomorph evolution, producing contradictory conclusions. Studies of included groups may be useful. Here, we study factors driving tethysuchian evolution using phylogenetically informed statistical analyses. First, we tested the phylogenetic structure of tethysuchian extinction at the OAE 2 and K/Pg crises. We then used phylogenetic comparative methods to test the influence of intrinsic (body size, snout proportion) and extrinsic (temperature, paleolatitude) factors on the evolution of tethysuchian diversity at the OAE 2 and the K/Pg crises. Finally, we tested whether temperature influenced the evolution of body size. We conclude that (1) extinction was not random in regard to phylogeny for Tethysuchia at the OAE 2 and K/Pg crises; (2) while an important tethysuchian turnover follows OAE 2, the K/Pg crisis was followed by an explosion in diversity of tethysuchians, probably linked to the colonization of emptied ecological niches; (3) tethysuchians lived in warmer environments after the OAE 2 crisis, possibly because of both global warming and latitudinal distribution shifts; (4) there is a significant change of snout proportion after the OAE 2 and the K/Pg crises, likely caused by niche partitioning; and (5) there is a positive correlation between body size and temperature, possibly because of a longer growth season.

Theropods are bipedal dinosaurs that appeared 230 million years ago and are still extant as birds. Their history is characterized by extreme variations in body mass, with gigantism evolving independently and on several occasions between many theropod groups. However, no study has shown whether all theropods evolved the same limb adaptations to high body mass or whether they had different morphologies. Here we studied the shape variation across 68 femora from 41 species of theropods using a 3D comparative approach, multivariate statistics, and phylogenetically informed analyses. We demonstrated that all the heaviest theropods evolved similar adaptations regardless of their phylogenetic affinities by enlarging muscular attachments and articular surfaces. We also highlighted that the lightest theropods evolved femoral adaptations to miniaturization, which occurred close to the bird lineage (Avialae). In addition, our results support a gradual evolution of known “avian” features, independent from body mass variations, which may relate to a more “avian” type of locomotion, where the knee drives hindlimb movement instead of the hip, like in earlier theropod relatives. The distinction between body mass variations and a more “avian” locomotion is represented by a decoupling in the mediodistal crest morphology, whose biomechanical nature should be studied to better understand the importance of its functional role in gigantism, miniaturization, and the evolution of a more “avian” type of locomotion.

Theropods are obligate bipedal dinosaurs that appeared 230 Ma and are still extant as birds. Their history is characterized by extreme variations in body mass, with gigantism evolving convergently between many lineages. However, no quantification of hindlimb functional morphology has shown whether these body mass increases led to similar specializations between distinct lineages. Here we studied femoral shape variation across 41 species of theropods (n = 68 specimens) using a high-density 3D geometric morphometric approach. We demonstrated that the heaviest theropods evolved wider epiphyses and a more distally located fourth trochanter, as previously demonstrated in early archosaurs, along with an upturned femoral head and a mediodistal crest that extended proximally along the shaft. Phylogenetically informed analyses highlighted that these traits evolved convergently within six major theropod lineages, regardless of their maximum body mass. Conversely, the most gracile femora were distinct from the rest of the dataset, which we interpret as a femoral specialization to “miniaturization” evolving close to Avialae (bird lineage). Our results support a gradual evolution of known “avian” features, such as the fusion between lesser and greater trochanters and a reduction of the epiphyseal offset, independent from body mass variations, which may relate to a more “avian” type of locomotion (more knee than hip driven). The distinction between body mass variations and a more “avian” locomotion is represented by a decoupling in the mediodistal crest morphology, whose biomechanical nature should be studied to better understand the importance of its functional role in gigantism, miniaturization, and higher parasagittal abilities.

In this study, we performed further microstructural studies of the eggshells of elongatoolithid eggs from China. We found that more diverse calcite crystal morphologies exist in these eggshells than were previously known. While excluding pathological structures, we also found evidence that some eggshells previously identified as elongatoolithid actually do not belong to this group. This study provides important data for the comparison of related fossil and extant eggshells.

Electron backscatter diffraction (EBSD) has been widely used in recent studies of eggshells for its convenience in collecting in situ crystallographic information. China has a wide variety of dinosaur eggshells, although nearly none have been studied with this technique. Elongatoolithid eggs include many oogenera, although the microstructural differences of some were not highly appreciated, leading to several parataxonomic problems. In this paper, we surveyed seven elongatoolithid oogenera in China using EBSD in order to acquire more information about their microstructural variation. It is shown in this paper that in some elongatoolithid eggshells, scaly calcite grains that form the squamatic ultrastructure are not the only form of calcite in the continuous layer. Large columnar grains separated by high-angled grain boundaries and slender subgrains separated by radially arranged low-angled grain boundaries could exist in certain areas of the eggshells such as Macroolithus and Macroelongatoolithus. This paper discusses the criteria for identifying squamatic ultrastructure and proposes type I (rich in rugged high-angled grain boundaries) and type II (rich in both rugged high- and low-angled grain boundaries) squamatic ultrastructures. A pathological layer is found in Undulatoolithus pengi. An external zone is identified in the eggshell of Heishanoolithus changii, which does not support its position within the oofamily Elongatoolithidae. We argue that Paraelongatoolithus no longer belongs to Elongatoolithidae based on a combination of reticulated ornamentation, columnar continuous layer, and acicular mammillae. The high structural variation in elongatoolithid eggshells also implies that it may be inappropriate to relate all previous elongatoolithid eggshells to oviraptorosaurs and assume they are non-monophyletic.

Complex enamel ridges have evolved multiple times on the teeth of unrelated aquatic predators, including extinct marine reptiles, toothed whales, crocodilians, and aquatic-feeding dinosaurs. Their appearance in such a wide range of groups suggests that they are a specialized structure adapted to perform specific functions in the capture and/or processing of prey, although these functions are unknown. This study used computer modeling to apply bite force simulations to a set of digital tooth models in order to identify whether the ridges strengthened the tooth. These models enabled us to visualize how bite force stress is distributed around smooth teeth compared with ridged teeth, including a range of ridge types. Our results suggested that the ridges do not strengthen the tooth crown overall, indicating that they may instead serve another role in prey handling.

Apicobasal ridges are longitudinal ridges of enamel that are particularly common in several clades of aquatic-feeding predatory amniotes, including Plesiosauria, Ichthyosauria, Mosasauridae, Crocodylia, and Spinosauridae, as well as some early members of Cetacea. Although the repeated evolution of these dental ridges in unrelated clades suggests an adaptive benefit, their primary function in feeding is debated. Hypothesized functions range from increasing tooth strength to improving prey puncture or removal efficiency, but these have never been quantitatively tested. This study utilizes finite element analysis (FEA) to assess the impact of apicobasal ridges upon tooth crown strength in aquatic-feeding amniotes. Drawing on morphometric data from fossilized tooth crowns, a set of digital models was constructed to calculate the performance of smooth and ridged tooth variants under simulated bite force loadings. The similarities in overall stress distribution patterns across models of the same tooth shape, regardless of the presence or morphology of ridges, indicate that apicobasal ridges have little impact on stress reduction within the tooth crown. Ultimately, these findings suggest that apicobasal ridges have a minimal role in improving crown strength and form a framework for future research into the remaining hypotheses.

During the late Miocene and early Pliocene about 5.7 to 4.75 million years ago, a distinctive suite of four species of extinct horses (Family Equidae) were widespread in North America. This includes Nannippus aztecus, Neohipparion eurystyle, Astrohippus stocki, and Dinohippus mexicanus. In Florida, two additional horse species, Pseudhipparion simpsoni and Cormohipparion emsliei, are also typically found. Here we compare horses from four Florida fossil sites of this age, including three from the Bone Valley mines and a fourth from the recently discovered Montbrook site. Two of these sites have all six predicted species, one has five species, and one has only four species present. To explain these differences, we used species occurrences from research databases to better understand the relative abundances, species richness, and occurrences of these horses from these four sites. One site (Palmetto Mine Agrico), with five equid species, appears to lack the sixth species owing to ecological reasons. This is different from Montbrook, the site with only four of the six species. Results indicate that Montbrook is likely missing the two horse species for a couple of reasons: sampling bias and biological/ecological causes. Our results demonstrate that fossil sampling biases can account for observed horse species occurrences when the overall abundance of certain species is low. Nevertheless, other factors, including ecology and with sufficient resolution, perhaps also time, may also explain the distribution and occurrences of individual horse species at these and other fossil sites.

During the late Miocene and early Pliocene (latest Hemphillian, Hh4 interval, 5.7 to 4.75 Ma) a distinctive suite of four species of extinct horses (Family Equidae) were widespread in North America. This includes Nannippus aztecus, Neohipparion eurystyle, Astrohippus stocki, and Dinohippus mexicanus. In Florida, two additional equid species, Pseudhipparion simpsoni and Cormohipparion emsliei, are also typically found at Hh4 localities. Here we compare horses from four Hh4 Florida fossil sites, including three from the Bone Valley mines and a fourth from the recently discovered Montbrook site. Two of these sites have all six expected species, one has five species, and one has only four species present. To explain these differences, we used species counts from research databases and rarefaction simulation to clarify the relative abundances, species richness, and occurrences of these horses from these four sites. The Palmetto Mine (Agrico) site, with five equid species, appears to lack the sixth species owing to ecological reasons. This is different from Montbrook, the site with only four of the six species. Results indicate that Montbrook is likely lacking two missing equid species for a couple of reasons: sampling bias and biological/ecological causes. Our results demonstrate that sampling biases can account for observed equid species richness when the overall abundance of certain equid species is low. Nevertheless, other factors, including ecology and with sufficient resolution, perhaps also time, may also explain the distribution and occurrences of individual species at these and other fossil sites. In a broader perspective, analyses such as this example provide an opportunity to address a persistent challenge in paleontology, that is, how do we explain absences of extinct taxa from the fossil record?

Is it environment or life that drives macroevolution? A recent analysis of the massive paleobiology database argues that the answer depends on the timescale. At short timescales, less than 40 million years, it is the environment, at longer timescales, life can effectively adapt. Both the environment and life are scaling—they fluctuate over the full range of scales from millions to hundreds of millions of years (the megaclimate regime). In this paper, we present a simple model of this scaling “crossover” phenomenon. The model has some unusual features: it is fully random and is based on fractional (rather than classical integer-ordered) differential equations.

The model is driven by temperature (a proxy for the environment) and the turnover rate (a proxy for life); it has two exponents, a cross-over time and two correlations, yet it is able to reproduce not only the statistics of the temperature, diversity, extinction, origination, and turnover rates, but it also effectively reproduces the pairwise correlations between them, and this over the whole range of timescales. If forced deterministically, it gives the response to bolide impact or other sharp forcing events.

Scaling fluctuation analyses of marine animal diversity and extinction and origination rates based on the Paleobiology Database occurrence data have opened new perspectives on macroevolution, supporting the hypothesis that the environment (climate proxies) and life (extinction and origination rates) are scaling over the “megaclimate” biogeological regime (from ≈1 Myr to at least 400 Myr). In the emerging picture, biodiversity is a scaling “crossover” phenomenon being dominated by the environment at short timescales and by life at long timescales with a crossover at ≈40 Myr. These findings provide the empirical basis for constructing the Fractional MacroEvolution Model (FMEM), a simple stochastic model combining destabilizing and stabilizing tendencies in macroevolutionary dynamics, driven by two scaling processes: temperature and turnover rates.

Macroevolution models are typically deterministic (albeit sometimes perturbed by random noises) and are based on integer-ordered differential equations. In contrast, the FMEM is stochastic and based on fractional-ordered equations. Stochastic models are natural for systems with large numbers of degrees of freedom, and fractional equations naturally give rise to scaling processes.

The basic FMEM drivers are fractional Brownian motions (temperature, T) and fractional Gaussian noises (turnover rates, E₊) and the responses (solutions), are fractionally integrated fractional relaxation noises (diversity [D], extinction [E], origination [O], and E_– = O– E). We discuss the impulse response (itself representing the model response to a bolide impact) and derive the model's full statistical properties. By numerically solving the model, we verified the mathematical analysis and compared both uniformly and irregularly sampled model outputs with paleobiology series.