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.

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.

Over the interval 2008–2023 a large number of studies have been published testing various aspects of punctuated equilibria, including the prevalence of stasis, and also the extent to which most evolutionary change is concentrated at cladogenesis. In the vast majority of studies, punctuated equilibria continued to be strongly validated, as widespread evidence for stasis accumulated, with only some rare incidences of gradual change found. Support for the importance of cladogenetic change has increased, and new analytical approaches to study punctuated equilibria have been developed. Over this time period, there has also been an increase in the number of studies that have concentrated on extant taxa to test for punctuated equilibria, and these have also corroborated its widespread presence. In this respect, punctuated equilibria has served as an important bridge between neontological and paleontological approaches to evolutionary biology. From 2008 to 2023, there has also been some drift in how stasis is defined, such that, in certain studies, the definition diverged from the original 1972 definition in important respects. Notably, it is the few studies that have most changed the definition of what stasis constitutes that have most challenged the validity of punctuated equilibria, indicating it is morphing interpretations and definitions rather than the discovery of data compatible with phyletic gradualism that are most responsible for divergent results.

A primary tenet of punctuated equilibria (PE) is that stasis, that is, little to no net morphological change, characterizes the histories of species. In the past ~50 years since PE was proposed, stasis has been recognized in the evolutionary histories of many species, but consensus has not been reached concerning its causes.

One unresolved issue is whether viable ecological mechanisms for stasis exist. We argue that a promising potential ecological explanation for stasis is coevolutionary alternation, which addresses how antagonists (e.g., predators or parasites and their groups of victims) coevolve over eco-evolutionary time across broad spatial scales. Coevolutionary alternation predicts different patterns of predator preferences and prey defenses within different populations and alternation of high and low levels of prey defenses as predator preferences evolve. The geographic structure of populations experiencing different environmental pressures and coevolutionary dynamics can yield stasis in such traits on the scale of entire species. We suggest that predator–prey coevolutionary alternation could be modeled using coupled stochastic differential equations (SDEs), which have been used to study correlative and causal connections among time series. SDEs can handle irregular sampling intervals, measurement uncertainty, and feedback loops between time series and can incorporate environmental proxies and time series from multiple geographic locations. We advocate developing this approach further to test the role of coevolutionary alternation in stasis and make recommendations for how SDEs might be used to model the coevolutionary feedback of predator(s) and multiple prey populations evolving in response to one another across space in a constantly changing environment.

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.

Genome size (GS) is thought to be a key life-history trait and important for controlling plant distributions and evolutionary dynamics, but a full understanding of GS variation through evolutionary history requires proxy measurements from fossils. Here, we compare two potential GS proxies: guard cell length (GCL) and sporomorph size. We generated GCL and pollen size data from angiosperms growing in the University of Münster Botanical Garden, compiled sporomorph size data from the literature, and related these to GS using phylogenetic regression models. We also fit evolutionary models to the botanical garden data and used a published dataset to validate GCL as a GS proxy. The majority of the analyses conducted revealed a positive relationship between GS and sporomorph size, but in most cases, the explanatory power of the regressions was low. GCL showed a stronger and more consistent relationship with GS, and independent validation of the relationship showed a generally good match between predicted and observed GS. Sporomorph size is not suitable as a cross-taxon GS proxy, but some specific taxa (e.g., Pinus) may contain useful GS information. GCL has much more potential for measuring paleo-GS, but requires further research for us to better understand possible environmental controls on cell size variation.

Despite its many extensions and implications, we argue that punctuated equilibrium itself has two core, empirical claims: (1) stasis dominates within fossil species; and (2) morphological change is concentrated in pulses that occur associated with speciation. Here we assess the state of the evidence for these two claims, 50 years after punctuated equilibrium’s foundational paper. Spurred by controversy, paleontologists have amassed a large number of case studies in which morphology in species-level lineages is tracked over time. Modern, likelihood-based methods have been used to fit to these data models of stasis, random walks, and directional trends, as well as more complex dynamics. Compilations reveal that the directional trends predicted by gradualist expectations are infrequent. Although stasis is commonly observed, it is favored in less than half of cases, and meandering random walks or more complex models generally account for the majority of cases. The second claim of punctuated equilibrium has received much less empirical scrutiny than the first. Although speciational pulses are plausible in theory, only a few paleontological studies integrate ancestor–descendant time series into a phylogenetic framework as is needed to estimate cladogenetic change and compare it with anagenesis. These studies, as well as more indirect analyses of extant clades, suggest that speciational change can occur, but we cannot yet assess with confidence its frequency or importance compared with anagenetic changes.

Although the theory of punctuated equilibria has stood the test of time, critics have sometimes highlighted the lack of a complementary molecular mechanism. The developmental gene hypothesis (DGH) provides just such a mechanism and is reviewed and significantly expanded in the present paper, taking advantage of concepts of active and passive evolvability, genetic drift, and the nearly neutral theory of molecular evolution, and compensatory adaptation in the face of weakly deleterious genetic variation. In addition, with the use of game theory, the author models the behavior of developmental regulatory (DevReg) genes, which are integral to the proposed hypothesis, in order to better understand their roles in stasis and speciation.

Toothed whales (odontocetes) make use of high-frequency sounds to echolocate, differing significantly from their sister group baleen whales (mysticetes), which make use of low-frequency sound for long-distance communication. This divergence in auditory ability has led to considerable speculation as to how hearing functioned in the ancestral archaeocetes, and when the specializations of modern species arose. Numerous studies have attempted to infer auditory capabilities from morphological correlates valid in modern species. Here, we build upon these previous methods with a focus on cochlear structures that have well-understood links to function. We combine this with information on the sound conduction apparatus to chart the evolutionary trajectory of cetacean hearing. Our results suggest an initial move toward low-frequency specialization in early Eocene cetaceans, which coincides with the appearance of new sound conduction pathways. This paved the way for the later movement toward higher-frequency hearing in protocetids; however, the ultra-high- and low-frequency hearing specializations of both modern cetacean clades evolved after their divergence. We use these data to test the hypotheses that evolutionary brain size increases in cetaceans were related to the origin of high-frequency echolocation. We show that no shift in relative brain size coincides with any changes toward high-frequency perception. However, this does not rule out a role for other changes in hearing ability such as some simple forms of echolocation, similar to that suggested for hippopotamuses or bowhead whales, which may have been present in even the earliest cetaceans.

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.

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.

In the last 50 years, the field of paleobiology has undergone a computational revolution that opened multiple new avenues for recording, storing, and analyzing vital data on the history of life on Earth. With these advances, the amount of data available for research has grown, but so too has our responsibility to ensure that our data tools and infrastructures continue to innovate in order to best serve our diverse community. This review focuses on data equity in paleobiology, an aspirational goal, wherein data in all forms are collected, stored, shared and analyzed in a responsible, equitable, and sustainable manner. While there have been many advancements across the last five decades, inequities persist. Our most significant challenges relate to several interconnected factors, including ethical data collection, sustainable infrastructure, socioeconomic biases, and global inequalities. We highlight the ways in which data equity is critical for paleobiology and stress the need for collaborative efforts across the paleobiological community to urgently address these data equity challenges. We also provide recommendations for actions from individuals, teams, academic publishers, and academic societies in order to continue enhancing data equity and ensuring an equitable and sustainable future for our field.

Incorporating paleontological data into phylogenetic inference can greatly enrich our understanding of evolutionary relationships by providing insights into the diversity and morphological evolution of a clade over geological timescales. Phylogenetic analysis of fossil data has been significantly aided by the introduction of the fossilized birth–death (FBD) process, a model that accounts for fossil sampling through time. A decade on from the first implementation of the FBD model, we explore its use in more than 170 empirical studies, summarizing insights gained through its application. We identify a number of challenges in applying the model in practice: it requires a working knowledge of paleontological data and their complex properties, Bayesian phylogenetics, and the mechanics of evolutionary models. To address some of these difficulties, we provide an introduction to the Bayesian phylogenetic framework, discuss important aspects of paleontological data, and finally describe the assumptions of the models used in paleobiology. We also present a number of exemplar empirical studies that have used the FBD model in different ways. Through this review, we aim to provide clarity on how paleontological data can best be used in phylogenetic inference. We hope to encourage communication between model developers and empirical researchers, with the ultimate goal of developing models that better reflect the data we have and the processes that generated them.

The Pleistocene/Holocene transition furnishes a classic example of apparent evolutionary stasis during a period of major environmental change, where observed environmental clines might predict evolutionary change. We have previously attempted to assess whether or not body size and shape were static in the extensive Quaternary vertebrate fauna of Rancho La Brea (RLB). However, the validity of time-series studies depends on dating, and there are indications that previous approaches based on pit mean radiocarbon ages may be misleading. Here we have compiled and recalibrated all available RLB radiocarbon ages, reanalyzed our morphometric data using a novel method for bootstrap resampling of calibrated C age distributions to estimate a time series of populations, and fit the time series with a range of simple evolutionary time-series models.

Although the shortness of our time series tends to favor nondirectional models and is insufficient to allow reliable discrimination between punctuated and gradual change, the results can still be clearly interpreted. The population means for most anatomical elements in most species at RLB do genuinely appear to be static through the Pleistocene/Holocene transition, as previously published. Some species exhibit previously undetected changes in population mean size and shape, including Smilodon, Gymnogyps, and Equus. However, the timing of change is variable among the non-static species and generally does not correspond to changes in temperature, and thus resists a Bergmann’s rule interpretation. Considering the species by ecological category may reveal more about the effects of climate regime shifts.

Most species exhibit morphological stasis following speciation, and this is a key feature of the concept of punctuated equilibria. Stasis results in species often having long durations on geological timescales. Durational data are fundamental to many types of paleobiological analyses and are ideally based on occurrence data represented by specimens in museum collections. Often, however, durational data are presented without supporting information about voucher specimens that document stratigraphic ranges, including first and last appearances. We use the iconic Devonian trilobite Eldredgeops rana to demonstrate that durational data can be challenging to determine at multiple taxonomic levels. Further, we show that different datasets—including Sepkoski’s published databases, the Paleobiology Database, and iDigBio—give discordant results concerning first and last occurrences. We argue that paleontologists should adopt two general best practices to help address these problems. First, systematists should clearly identify voucher specimens that represent stratigraphic occurrences of species. Second, we recommend that high-quality photographs of occurrence vouchers be placed in open access websites and be assigned public domain licensing before being paywalled by journals. Such voucher images also have a role to play in training artificial intelligence (AI) systems that will be applied to future paleobiological questions.

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 Neotropics host the highest diversity of plants on the Earth today and have done since at least the late Paleogene (~58 Ma). Several mechanisms have been proposed to explain this elevated diversity, but the empirical patterns of Neotropical plant diversification that would test key aspects of those mechanisms are still unclear. We use an extensive palynological database from northern South America to characterize patterns of extinction, origination, and diversity and their possible drivers since the Paleogene. The foreland Llanos basin of Colombia preserves the evolutionary history of Neotropical vegetation as well as the geological evolution of northern South America, offering a unique opportunity to study the relationship between the geological and fossil records. The palynological record of the Llanos basin has been intensely studied mainly for oil exploration, and we use this information to infer the evolutionary history of Neotropical vegetation in Colombia during the Cenozoic. There is no straightforward relationship between global temperature and Neotropical plant diversity. Nevertheless, environmental change had an important influence on the dynamics of diversification, especially during volatile climate intervals such as the Paleocene–Eocene and the Pleistocene. Pulses of regional extinction were driven by large-scale temperature excursions, including both warming and cooling phases. Time-lagged origination pulses results in rapid floral replacement on a timescale of 1 Myr. Origination and extinction are essentially balanced on long timescales, leading to a near-zero long-term net diversification rate. Regional geological events, like the uplift of the Andean Cordillera, and changes in paleogeography also played an important role in Neotropical plant diversification.

The first compilations of Proterozoic eukaryote diversity, published in the 1980s showed a dramatic peak in the Tonian Period (1000–720 Ma), interpreted as the initial radiation of eukaryotes in the marine realm. Over the decades, new discoveries filled in the older part of the record and the peak diminished, but the idea of a Tonian radiation of eukaryotes has remained strong, and is now widely accepted as fact. We present a new diversity compilation based on 181 species and 713 species occurrences from 145 formations ranging in age from 1890 Ma to 720 Ma and find a significant increase in diversity in the Tonian. However, we also find that the number of eukaryotic species through time is highly correlated with the number of formations in our dataset (i.e. eukaryote-bearing formations) through time. This correlation is robust to interpretations of eukaryote affinity, bin size, and bin boundaries. We also find that within-assemblage diversity—a measure thought to circumvent sampling bias—is related to the number of eukaryote-bearing formations through time. Biomarkers show a similar pattern to body fossils, where the rise of eukaryotic biosignatures correlates with increased sampling. We find no evidence that the proportion of eukaryote-bearing versus all fossiliferous formations changed through the Proterozoic, as might be expected if the correlation reflected an increase in eukaryote diversity driving an increase in the number of eukaryote-bearing formations. Although the correlation could reflect a common cause such as changes in sea level driving both diversification and an increase in sedimentary rock volume, we favor the explanation that the pattern of early eukaryote diversity is driven by variations in paleontological sampling.