Paleobiology was founded 50 years ago to provide an outlet for biological paleontology, with an emphasis on investigating evolutionary patterns and processes that could apply generally across the history of life. While the intellectual and financial prospects for Paleobiology were uncertain in the beginning (Sepkoski 2012; Valentine 2009), this 50th anniversary issue testifies to its overwhelming success. Fifty years of anything well done deserves a celebration. These moments are a time for reflection and a time for imagining future directions. With this introduction, we outline briefly the start of the journal and two landmark anniversary issues, the 10th and the 25th. No special issue can adequately survey all research themes in a field as intellectually rich as paleobiology. However, these anniversary issues offer a snapshot of research directions, and they can trace the shift and expansion of established fields and mark the emergence of new ones. We end by outlining the contributions to the 50th anniversary issue that summarize current themes and future directions for the field.

Prospective and early-career paleontologists deserve an accurate assessment of employment opportunities in their chosen field of study. Drawing on a wide range of sources, we have produced an admittedly incomplete analysis of the current status and recent trends of permanent academic employment in the discipline. Obtaining more complete longitudinal data on employment trends is a major difficulty; this is a challenge that needs to be addressed. The number of job seekers is far in excess of available positions. There has been a clear erosion in the number of academic paleontologists in the United States, a trend exacerbated in recent years. The decline, in constant dollars, of federal funding for paleontological research has potential strong negative impacts on future hiring. The loss of paleontology positions has also had a deleterious effect on our professional societies, which have seen a loss of regular (professional) membership, although student membership remains strong. These trends also potentially negatively impact efforts to diversify the field. Professional societies need to better coordinate their efforts to address these serious issues. Individual paleontologists also must become more effective advocates for the importance and relevance of our science.

Fossil pollen analysis is an “open-world” problem in paleontology for which there is a long-standing need for automated identification and classification. In the open world, categorical classes are imbalanced, test classes are not known a priori, and test data are captured across different domains. Pollen samples capture large numbers of specimens that include both common and abundant types and rare and sometimes novel taxa. Pollen is diverse morphologically and features can be altered during fossilization. Additionally, there is little standardization in the imaging of pollen samples. Therefore, generalized workflows for automated pollen analysis require techniques that are robust to these differences and can work with microscope images. We focus on a critical first step, the initial detection of pollen specimens on a palynological slide and review how existing methods can be employed to build robust and generalizable analysis pipelines. First, we demonstrate how a mixture-of-experts approach—the fusion of a general pollen detector with an expert model trained on minority classes—can be used to address taxonomic biases in detections, particularly the missed detections of rarer pollen types. Second, we demonstrate the efficiency of domain fine-tuning in addressing domain gaps—differences in image magnification and resolution across microscopes and of taxa across different sample sources. Third, we demonstrate the importance of continual learning workflows, which integrate expert feedback, in training detection models from incomplete data. Finally, we demonstrate how cutting-edge segmentation models can be used to refine and clean detections for downstream deep learning classification models.

The spatial distribution of individuals within ecological assemblages and their associated traits and behaviors are key determinants of ecosystem structure and function. Consequently, determining the spatial distribution of species, and how distributions influence patterns of species richness across ecosystems today and in the past, helps us understand what factors act as fundamental controls on biodiversity. Here, we explore how ecological niche modeling has contributed to understanding the spatiotemporal distribution of past biodiversity and past ecological and evolutionary processes. We first perform a semiquantitative literature review to capture studies that applied ecological niche models (ENMs) to the past, identifying 668 studies. We coded each study according to focal taxonomic group, whether and how the study used fossil evidence, whether it relied on evidence or methods in addition to ENMs, spatial scale of the study, and temporal intervals included in the ENMs. We used trends in publication patterns across categories to anchor discussion of recent technical advances in niche modeling, focusing on paleobiogeographic ENM applications. We then explored contributions of ENMs to paleobiogeography, with a particular focus on examining patterns and associated drivers of range dynamics; phylogeography and within-lineage dynamics; macroevolutionary patterns and processes, including niche change, speciation, and extinction; drivers of community assembly; and conservation paleobiogeography. Overall, ENMs are powerful tools for elucidating paleobiogeographic patterns. ENMs are most commonly used to understand Quaternary dynamics, but an increasing number of studies use ENMs to gain important insight into both ecological and evolutionary processes in pre-Quaternary times. Deeper integration with traits and phylogenies may further extend those insights.

Paleontology provides insights into the history of the planet, from the origins of life billions of years ago to the biotic changes of the Recent. The scope of paleontological research is as vast as it is varied, and the field is constantly evolving. In an effort to identify “Big Questions” in paleontology, experts from around the world came together to build a list of priority questions the field can address in the years ahead. The 89 questions presented herein (grouped within 11 themes) represent contributions from nearly 200 international scientists. These questions touch on common themes including biodiversity drivers and patterns, integrating data types across spatiotemporal scales, applying paleontological data to contemporary biodiversity and climate issues, and effectively utilizing innovative methods and technology for new paleontological insights. In addition to these theoretical questions, discussions touch upon structural concerns within the field, advocating for an increased valuation of specimen-based research, protection of natural heritage sites, and the importance of collections infrastructure, along with a stronger emphasis on human diversity, equity, and inclusion. These questions offer a starting point—an initial nucleus of consensus that paleontologists can expand on—for engaging in discussions, securing funding, advocating for museums, and fostering continued growth in shared research directions.

Life-history traits such as dispersal affect population attributes like gene flow, which can have consequences for speciation and extinction rates over macroevolutionary timescales. Here we use the Cheilostomatida, a monophyletic order of marine bryozoans, to test whether a life-history trait, larval brooding, affected the origination and extinction rates of genera throughout their fossil record. Cheilostome lineages that brood their larvae have shorter larval dispersal distances than non-brooding lineages, which has led to the hypothesis that the evolution of larval brooding decreased gene flow, increased origination, and drove their Cretaceous diversification. Brooding cheilostomes are far more diverse than non-brooding cheilostomes today, but it remains to be shown that brooding lineages have a higher origination rate than non-brooders. We fit time-varying Pradel seniority capture–mark–recapture models to look at the effect of brooding on origination and extinction rates during the Cretaceous cheilostome diversification, the Cretaceous/Paleogene mass extinction and recovery, and through the Cenozoic. Our results support the hypothesis that brooding affects origination rate, but only in the Cenomanian to Campanian. Extinction rates do not differ between brooding and non-brooding genera, and there is no regime shift specific to the Cretaceous/Paleogene mass extinction. Our work illustrates the importance of using fossil occurrences and time-varying models, which can detect interval-specific diversification differentials.

Over the last 50 years, paleobiology has made great strides in illuminating organisms and ecosystems in deep time through study of the often-curious nature of the fossil record itself. Among fossil deposits, none are as enigmatic or as important to our understanding of the history of life as Konservat-Lagerstätten, deposits that preserve soft-bodied fossils and thereby retain disproportionately large amounts of paleobiological information. While Konservat-Lagerstätten are often viewed as curiosities of the fossil record, decades of study have led to a better understanding of the environments and circumstances of exceptional fossilization.Whereas most types of exceptional preservation require very specific sets of conditions, which are rare but can occur at any time, Seilacher noted the problem of “anactualistic” modes of exceptional preservation, defined as modes of fossilization that are restricted in time and that no longer occur. Here, we focus on anactualistic preservation and the widely recognized overrepresentation of Konservat-Lagerstätten in the Ediacaran and early Paleozoic. While exceptional fossil deposits of Ediacaran, Cambrian, and Early Ordovician age encompass a number of modes of fossilization, the signal of exceptional preservation is driven by only two modes, Ediacara-type and Burgess Shale–type preservation. Both are “extinct” modes of fossilization that are no longer present in marine environments. We consider the controls that promoted widespread anactualistic preservation in the Ediacaran and early Paleozoic and their implications for the environmental conditions in which complex life first proliferated in the oceans.

Body mass is an important facet of reconstructing the paleobiology of fossil species and has, historically, been estimated from individual skeletal measurements. This paper demonstrates the potential advantages of estimating body mass using 3D geometric morphometrics on limb bones, which allows size to be explicitly contextualized within the functional morphology of the animal. Geometric morphometrics of the humerus and femur is used to estimate body mass in domestic dogs and wild canids, and the resulting estimates are compared with estimates made using limb bone dimensions and centroid size. In both groups, 3D methods produced more accurate estimates of body mass than linear dimensions. Additionally, centroid size was a poor predictor of body mass and should not be preferred over linear measurements. The use of 3D methods also reveals specific aspects of shape that are associated with different sizes. In general, relatively heavier individuals were associated with more robust bones and wider articulation sites, as well as larger attachment sites for muscles related to flexion and extension of the shoulder and hip joints. The body-mass equations constructed based on dogs were further evaluated on wild canids, as a test of their potential efficacy on fossil canids. With some adjustments, the body-mass estimation equations made for domestic dogs were able to reliably predict the mass of wild canids. These equations were then used to estimate body mass for a selection of fossil canids: Canis latrans, 16 kg; Aenocyon dirus, 67 kg; Phlaocyon multicuspus, 8 kg; and Hesperocyon gregarius, 2.5 kg.

The present-day climate crisis is transforming coral reef communities, potentially undermining ecosystem functioning. Evolutionary trade-offs between species traits result in diverse life-history strategies, enabling corals to survive disturbance events through specific adaptive mechanisms. Trait–trait relationship networks offer insights into trait turnover and changing life-history strategies during environmental changes. Paleoecological insights from the fossil records can further illustrate how species adapt to environmental shifts, highlighting resilience traits.

We highlight coral traits that promote resilience in the Caribbean based on fossil occurrences and morphological traits, examining biological determinants of species and trait turnover across the Cenozoic. We use traits that underpin the survival of corals during disturbances, for example, corallite diameter, colony growth form, corallite integration, and budding type. We analyzed species turnover and extinctions with a bipartite network and explored trait turnover with trait–trait co-occurrence networks based on 4268 species records at 421 sites over ~40 Myr.

Our findings support existing evidence that species turnover coincided with major environmental and biogeographic changes across the Cenozoic. Additionally, our results provide new insight into functional changes throughout the Cenozoic. Past cooler climates favored corals with a fast growing and reproducing (competitive) life-history strategy, which boosts short-term success, but also increases susceptibility to diseases and thermal stress. Cenozoic species and trait turnover occurred during environmental change, corroborating expectations of such turnover in the future. We found trait co-occurrence modules associated with competitive and stress-tolerant life-history strategies. The transition from the “greenhouse” (Paleogene) to the “icehouse” (Neogene) climate over ~40 Myr favored competitive traits, which supported fast-growing, shallow reefs. With rising temperatures and declining Acropora in the Caribbean, future reefs may resemble Eocene reefs: dominated by stress-tolerant, slow-growing corals adapted to marginal environments.

Stratigraphic paleobiology uses a modern understanding of the construction of the stratigraphic record—from beds to depositional sequences to sedimentary basins—to interpret patterns and guide sampling strategies in the fossil record. Over the past 25 years, its principles have been established primarily through forward numerical modeling, originally in shallow-marine systems and more recently in nonmarine systems. Predictions of these models have been tested through outcrop-scale and basin-scale field studies, which have also revealed new insights. At multi-basin and global scales, understanding the joint development of the biotic and sedimentary records has come largely from macrostratigraphy, the analysis of gap-bound packages of sedimentary rock. Here, we present recent advances in six major areas of stratigraphic paleobiology, including critical tests in the Po Plain of Italy, mass extinctions and recoveries, contrasts of shallow-marine and nonmarine systems, the interrelationships of habitats and stratigraphic architecture, large-scale stratigraphic architecture, and the assembly of regional ecosystems. We highlight the potential for future research that applies stratigraphic paleobiological concepts to studies of climate change, geochemistry, phylogenetics, and the large-scale structure of the fossil record. We conclude with the need for more stratigraphic thinking in paleobiology.

The evolution of mammalian innovations like elevated growth rates, endothermy, and live birth has been the subject of paleobiological work for decades. Bone histology provides one of the best lines of evidence for assessing growth rates and life-history traits in the fossil record. However, little ontogenetic information is available for nonmammalian cynodonts, the stock lineage that eventually gave rise to mammals. Here, I report the bone histology of two traversodontid cynodonts from the Triassic Manda Formation of Tanzania. Using two femoral size series, I correlate bone tissue composition and limb size in Scalenodon angustifrons and Luangwa drysdalli. Fifteen individuals were analyzed from seven penecontemporaneous localities to assess intraspecific histovariation within traversodontid ontogenetic development for the first time. My results show that Scalenodon and Luangwa have disparate life histories despite being similarly sized contemporaries. Luangwa is characterized by parallel-fibered bone that transitions to woven-parallel bone early in ontogeny, interpreted as a growth spurt. This increase in growth rate is seen in small- and middle-sized individuals but is resorbed and remodeled in the largest, skeletally mature individual. By contrast, Scalenodon is characterized by woven-parallel tissue in early ontogeny. However, femur size is not correlated with changes in bone tissue composition, as multiple individuals show peripheral slower-growing tissue regardless of size, interpreted as highly developmentally plastic growth. Together, these results demonstrate that coeval members of Traversodontidae show disparate life histories. The underlying mechanisms to explain different life histories in these taxa are likely due to (1) intrinsic differences in growth rates and (2) varying degrees of developmentally flexible growth. The implication of this work is that intraspecific variation in growth dynamics may be more widespread than currently understood in cynodonts and that size is not a good indicator of maturity for some species.

Paleo-ecological niche modeling (paleoENM) estimates the niches and distributions of extinct species using fossil paleo-coordinates and local environmental data. While general circulation models (GCMs) have been used to estimate climate conditions in deep time, primarily for terrestrial vertebrates, variations in paleo-elevation models used in GCM construction can influence paleoENM outcomes. This study (1) examines the impact of the Cretaceous–Paleogene (K-Pg) mass extinction on the niche dimensions of the marine invertebrate group Turritellinae (Cerithoidea: Turritellidae) and (2) compares two paleo-elevation models’ effects on GCM-based species’ distribution predictions. Fossil occurrence data from the Maastrichtian and Danian periods were collected from the Paleobiology Database (PBDB), museum collections, and published literature. Environmental data were extracted from HadCM3L GCM simulations using Scotese- and Getech-based paleogeographic and pCO2 boundary conditions. We estimated the niche dimensions of turritellines using maximum entropy (MaxEnt) and performed ordination analysis using kernel density estimation. MaxEnt model metrics showed that the Getech-based GCM outperformed the Scotese-based GCM. Geographic projections revealed minor differences in suitable habitat between the Maastrichtian and Danian in the Getech-based GCM, but overinflated predictions in the Scotese-based GCM. Niche overlap between the Maastrichtian and Danian was high, with both GCMs supporting niche similarity and equivalency. Our results suggest that differences in elevation model boundary conditions affected predicted distribution and niche patterns. This study offers a novel approach to understanding ecological persistence in invertebrates after mass extinction events, examines the robustness of GCM boundary conditions in paleoENM studies, and provides a framework for future paleoecological research on fossil invertebrates.

A central goal in ecology is investigating the impact of major perturbations, such as invasion, on the structure of biological communities. One promising line of inquiry is using co-occurrence analyses to examine how species’ traits mediate coexistence and how major ecological, climatic, and environmental disturbances can affect this relationship and underlying mechanisms. However, present communities are heavily influenced by anthropogenic behaviors and may exhibit greater or lesser resistance to invasion than communities that existed before human arrival. Therefore, to disentangle the impact of individual disturbances on mammalian communities, it is important to examine community dynamics before humans. Here, we use the North American fossil record to evaluate the co-occurrence structure of mammals across the Great American Biotic Interchange. We compiled 126 paleocommunities from the late Pliocene (4–2.5 Ma) and early Pleistocene (2.5–1 Ma). Genus-level co-occurrence was calculated to identify significantly aggregated (co-occur more than expected) and segregated (co-occur less than expected) genus pairs. A functional diversity analysis was used to calculate functional distance between genus pairs to evaluate the relationship between pair association strength and functional role. We found that the strength distribution of aggregating and segregating genus pairs does not significantly change from the late Pliocene to the early Pleistocene, even with different mammals forming the pairs, including immigrant mammals from South America. However, we did find that significant pairs, both aggregations and segregations, became more similar in their functional roles following the Plio-Pleistocene transition. Due to different mammals and ecological roles forming significant associations and the stability of co-occurrence structure across this interval, our study suggests that mammals have fundamental ways of assembling that may have been altered by humans in the present.

Organismal metabolic rate is linked to environmental temperature and oxygen consumption, and as such, may be a useful predictor of extinction risk. This is especially true during major climate-driven extinctions, given the tightly linked stressors of warming and hypoxia. However, metabolic attributes can be quantified in different ways, highlighting differing aspects of organisms’ ecology. Here, we estimate resting whole-body and mass-specific metabolic rates in post-Carboniferous bivalve taxa using body size, seawater paleotemperature, and a taxon-specific adjustment factor to assess how metabolic rate correlates with survival both during and outside intervals of rapid climate warming, or “hyperthermals.” Accounting for the effects of geographic range size, we find a pattern of preferential extinction of bivalves with lower total calorific needs, consistent with increasing body size and the postulated ramping up of ecosystem energetics over the Meso-Cenozoic. Contrary to expectations, extinction selectivity based on total calorific needs, which emphasizes body size, does not differ between hyperthermals and other time intervals. However, a higher metabolic rate per gram of tissue—which is more strongly determined by environmental temperature than by body size—consistently increases the probability of extinction during hyperthermals relative to baseline conditions, particularly within the paleotropics. This serves to highlight the potential significance of environmental temperature on metabolic performance, particularly in organisms that are already living close to their thermal limits. In tandem with previously documented patterns of extinction selectivity based on relative activity levels, including motility and feeding style, these results enhance our understanding of the role of metabolic rate through time and during climate-driven extinctions. When standardized by mass, metabolic rate may represent a useful metric through which to predict the effects of anthropogenic climate change on modern marine faunas.

The fitness of groups is often considered to be the average fitness among constituent members. This assumption has been useful for developing models of multilevel selection, but its uncritical adoption has held back our understanding of how multilevel selection actually works in nature. If group fitness is only equal to mean member fitness, then it is a simple task to erode the importance of group-level selection in all multilevel scenarios—species selection could then be reduced to organismal selection as easily as group selection can. Because selection from different levels can act on a single trait, body size, for example, there must be a way to translate one level of fitness to another. This allows the calculation of the contributions of selection at each level. If high-level fitness is not a simple function of member fitness, then how do they interlace? Here we reintroduce Leigh Van Valen’s argument for the inclusion of expansion as a component of fitness. We show that expansion is an integral part of fitness even if one does not subscribe to the energetic view of fitness from which Van Valen originally derived it. From a hierarchical perspective, expansion is the projection of demographic fitness from one level to the next level up; differential births and deaths at one level produce differential expansion one level above. Including expansion in our conceptual tool kit helps allay concerns about our ability to identify the level of selection using a number of methods as well as allowing for the various forms of multilevel selection to be seen as manifestations of the same basic process.

The Mazon Creek Lagerstätte (Moscovian Stage, late Carboniferous Period; Illinois, USA) captures a diverse view of ecosystems in delta-influenced coastal settings through exceptional preservation of soft tissues in siderite concretions. The generally accepted paradigm of the Mazon Creek biota has been that of an inferred paleoenvironmental divide between what have been termed the Braidwood and Essex assemblages, wherein the former represents a freshwater ecosystem with terrestrial input and the latter a marine-influenced prodelta setting with abundant cnidarians, bivalves, worm phyla, and diverse arthropods. Here, we revisit the paleoecology of the Mazon Creek biota by analyzing data from nearly 300,000 concretions from more than 270 locations with complementary multivariate ordinations. Our results show the Braidwood assemblage as a legitimate shoreward community and provide evidence for further subdivision of the Essex assemblage into two distinct subassemblages, termed here the Will-Essex and Kankakee-Essex. The Will-Essex represents a benthos dominated by clams and trace fossils along the transition between nearshore and offshore deposits. The Kankakee-Essex is dominated by cnidarians, presenting an ecosystem approaching the geographic margin of this taphonomic window. These new insights also allow a refined taphonomic model, wherein recalcitrant tissues of Braidwood organisms were subject to rapid burial rates, while organisms of the Essex assemblage typically had more labile tissues and were subject to slower burial rates. Consequently, we hypothesize that the Braidwood fossils should record more complete preservation than the Essex, which was exposed for longer periods of aerobic decomposition. This is supported by a higher proportion of non-fossiliferous concretions in the Essex than in the Braidwood.

Ostracoderms, Paleozoic jawless stem-gnathostomes, are characterized by distinctive bony shields covering the front of their bodies. These headshields exhibit significant variations in morphology across species, boasting frontal, lateral, and dorsal processes. Ostracoderms represent pivotal intermediaries between modern jawless and jawed vertebrates, so understanding their biology and ecology is crucial for unraveling the selective pressures that shaped the early evolution and diversification of jawed vertebrates, which now dominate vertebrate diversity. This study employs virtual paleontology techniques and phylogenetic comparative methods to explore the hydrodynamic and ecological implications of these processes, focusing on pteraspidomorphs, the most diverse ostracoderm group. The analysis reveals widespread convergence in the arrangement and development of headshield processes. Lateral processes enhance hydrodynamic efficiency and generate lift, while combined lateral and dorsal processes provide stability in rolling, yawing, and pitching. Frontal processes reduce drag in many cases. These findings illuminate the enigmatic roles of ostracoderm headshields, showing how the dimensions and arrangement of their processes are biomechanically linked to a range of functions and ecological roles. Collectively, this highlights the intricate evolutionary pathways of lifestyles and ecologies within stem-gnathostomes, challenging the idea of a unidirectional trend toward more active lifestyles in vertebrate evolution and suggesting diverse ecological roles for ostracoderms.

Every organism interacts with a host of other organisms of the same and different species throughout its life. These biotic interactions have varying influences on the reproduction and dispersal of the organism, and hence also the population and species lineage to which the organism belongs. By extension, biotic interactions must contribute to the macroevolutionary patterns that we observe in the fossil record, but exactly how, when, and why are research questions we have been asking before the start of the journal Paleobiology. In this contribution for Paleobiology’s 50th anniversary, we present a brief overview of how paleobiologists have studied biotic interactions and their macroevolutionary consequences, recognizing paleontology’s unique position to contribute data and insights to the topic of interspecies interactions. We then explore, in a semi-free-form manner, what promising avenues might be open to those of us who use the fossil record to understand biotic interactions. In general, we emphasize the need for increased effort surrounding the understanding of ecological details, integration of different types of information, and model-based approaches.

Ichthyosauria, Plesiosauria, and Metriorhynchidae were apex predators in Mesozoic oceanic trophic networks. Previous stable oxygen isotope studies suggested that several taxa belonging to these groups were endothermic and that some of them were homeothermic organisms. However, these conclusions remain contentious owing to the associated uncertainties regarding the δ18O value and oxygen isotope fractionation relative to environmental seawater. Here, we present new bioapatite phosphate δ18O values (δ18Op) of Ichthyosauria, Plesiosauria, and Metriorhynchidae (Middle Jurassic to Early Cretaceous) recovered from mid- to high paleolatitudes to better constrain their thermophysiology and investigate the presence of regional heterothermies. The intraskeletal δ18Op variability failed to reveal distinct heterothermic patterns within any of the specimens, indicating either intrabody temperature homogeneity or an overriding diagenetic overprint of the original biological δ18Op bone record. Body temperature estimates have been reassessed from new and published δ18Op values of well-preserved isolated teeth, recently revised Mesozoic latitudinal δ18O oceanic gradients, and 18O-enrichment factors of fully aquatic air-breathing vertebrates. Our results confirm that Ichthyosauria were homeothermic endotherms (31°C to 41°C), while Plesiosauria were likely poikilothermic endotherms (27°C to 34°C). The new body temperature estimates of the Metriorhynchidae (25°C to 32°C) closely follow ambient temperatures and point to poikilothermic strategy with no or little endothermic ability. These results improve our understanding of Mesozoic marine reptile thermoregulation and indicate that due to their limited body temperature variations, the δ18Op values from Ichthyosauria fossil remains could be used as valuable archives of Mesozoic oceans δ18Osw values that may help improve paleoenvironmental and paleoclimatic reconstructions.

The Great Ordovician Biodiversification Event (GOBE) records a global increase in marine biodiversity that reached maximum diversification rates during the Middle Ordovician. The degree to which the causes of the GOBE are regional or global is a question that must be addressed through analysis of regional data. In this study, stratigraphically constrained field-based data from the Middle Ordovician Simpson Group of Oklahoma were collected to identify temporal trends in body volume and determine whether body volume trends are more closely associated regional or global environmental and diversity changes. Anteroposterior–transverse (AT) volume estimations were produced for rhynchonelliform brachiopods at a bedding-plane level of resolution. Time-series analysis was used to establish temporal trends in brachiopod volume. Volume data were then analyzed alongside paired δ18O, Δ13C, 87Sr/86Sr, taxonomic diversity, and lithologic data using a boosted regression model to identify their relative influence on shell volume through time. Results of these analyses indicate that (1) a rapid pulse of brachiopod volume increase occurred coincident with the main diversification pulse in Simpson Group strata and (2) volume increase was not coupled with an increase in brachiopod volume variance. Volume increase was primarily associated with global-scale factors such as age, δ18O (temperature), 87Sr/86Sr (tectonics), and taxonomic diversity trends; whereas local-scale factors of Δ13C (carbon cycle) and lithologic trends were more weakly associated with local volume trends. Notably, all factors had a nonzero influence over brachiopod volume, indicating that local diversification was influenced by multifaceted interactions among abiotic and biotic controls. These results support the argument that Ordovician diversification included a substantial biotic shift during the Middle Ordovician and support the hypothesis that global factors were dominant, influencing diversification patterns during the main phase of the GOBE.