Abelisaurid dinosaurs display a remarkable diversity in cranial ornamentation, which includes several features such as rugosities, pits and grooves on the rostrum and orbital regions, midline knobs, and paired plus sculptured structures across the skull roof. To investigate macroevolutionary patterns that underlie this diversity, we tested the “species recognition” hypothesis using phylogenetic comparative methods. Our results indicate directional and ordered evolutionary patterns in cranial ornamentation that are more consistent with expectations of sexual selection than with the stochastic patterns predicted under the species recognition hypothesis. Moreover, sympatric species exhibited highly divergent ornamentation, and the degree of surface texturing and the development of certain structures (e.g., knobs) increased through ontogeny. These findings suggest that cranial ornamentation in Abelisaurids was influenced by mechanisms of sexual selection, sexual dimorphism, or mutual selection. Evolutionary modeling combined with evidence from the fossil record and phylogenetic correlation analysis reveals that the ornamentation of the rostrum and orbital regions was evolutionarily coupled and became canalized during the Early Cretaceous. In contrast, phylogenetic correlation analyses demonstrated that skull roof ornaments and rostral and orbital ornaments evolved decoupled. Neither discrete ornament traits nor the accumulation of traits over time showed significant associations with body size, indicating that ornament diversification in Abelisauridae was not constrained by allometric trends. During the Late Cretaceous, after refined ecological specialization, the subclades Carnotaurini and Majungasaurinae underwent further elaboration, acquiring features such as a prominent midline knobs, paired structures, and reinforced occipital and cervical regions. These derived morphologies may have facilitated more complex sociosexual behaviors.

Ceratopsian dinosaurs underwent great changes, including a shift of locomotion mode, enlarged horns and frills, and increased body size. These changes occur alongside the evolution of endocranial morphology and physiology such as the size and shape of the flocculus, hearing range, olfactory ratio, and the reptile encephalization quotient (REQ). However, the evolution of endocranial structures in early ceratopsians is still unclear because of a lack of information on the earliest ceratopsians. Here, we reconstructed the endocasts of three early-diverging ceratopsians including the Late Jurassic Yinlong, and the Early Cretaceous Liaoceratops and Psittacosaurus. These ceratopsians display obvious flocculi, large and separate olfactory bulbs, long and high anterior semicircular canals, and relatively long cochlear ducts. In the evolution of the earliest ceratopsians to early neoceratopsians, changes include the increasing size of the flocculus (which is reduced or absent in late-diverging ceratopsids), the attenuation of the semicircular canals, and the heightening of the anterior semicircular canal (which is shortened in late-diverging ceratopsids). The endocranial structures suggest early-diverging ceratopsians had a higher olfactory acuity and were adapted to hearing higher frequencies than late-diverging ceratopsians. Furthermore, the REQ suggests that Yinlong and Psittacosaurus were more highly encephalized than late-diverging ceratopsians and most extant reptiles. The angle of the lateral semicircular canal suggests that heads in ceratopsians display a transition from a forward posture to a more downward posture. Our new findings are significant for understanding the physiological changes during ceratopsian evolution and also have implications for the evolution of physiology in extant tetrapods.

Wing shape is integrally related to flight performance and function in extant animals. Analyzing this relationship in pterosaurs is complicated by the fragmentary nature of the fossil record and because the flight dimensions of wing membranes do not preserve. In the absence of fully extended pterosaur wing fossils, scientific reconstruction of the pterosaur Bauplan presents the clearest alternative for analysis. However, these wing shapes are subject to multiple conflicting scientific opinions and the artistic styles of the researchers and illustrators reconstructing them. Here we test the functional ramifications of different wing-shape reconstructions. We use theoretical morphospace analysis to establish whether modern reconstructions of pterosaur wings exhibit the diversification and functional performance expected of living animals. Pterosaur wing reconstructions show little by way of taxonomic separation either in shapespace or functional performance, with all pterosaur groups overlapping independent of time, size or proposed niche. This suggests that published pterosaur reconstructions underestimate the diversity of wing shapes expected of such a diverse group and are not reflective of flying animals. Stylistic approaches have little effect on the occupation and diversity of pterosaur reconstructions, suggesting that the underpinning issues lie in the lack of scientific consensus on the shape and structure of the wings, rather than how they are reconstructed.

Understanding cranial sutures and how they relieve and dissipate stress is essential to assess their role in cranial biomechanics and to develop highly accurate predictive models. This involves examining how ontogeny affects cranial sutures, as well as their morphology and function, and how these changes through time may impact essential biomechanical loadings such as chewing or direct biting. In this work, we study the cranial sutures of Crocodylus niloticus in detail using contact elements under finite element analysis. Contact elements permit the creation of a physical relationship between two bones that are in contact and even the configuration of these relationships, for example, in terms of movement or flexibility. The definition of bone contacts may require linear and/or nonlinear computational solutions to attain higher accuracy. Herein, skull geometry is tested to determine how bones may be altered by different types of contacts under various conditions. As predicted, the absence of sutures or cranial kinesis leads to a reduction in stress distribution across the skull, whereas sutures and cranial kinesis help the skull relieve stress and prevent certain bones from sustaining high stress levels. The type of contact used in individual sutures has a significant effect on model outcomes. Additionally, feeding behaviors significantly impact cranial biomechanics, reflecting the influence of other variables that may be applied to the models. As highlighted by the results, in order to obtain accurate results when analyzing fossil taxa, the nature of the cranial sutures should be taken into account. Therefore, developing predictive models based on living taxa is invaluable, because it facilitates the study of extinct taxa for which there is a lack of information on the fibrous joints due to poor or no preservation in the fossil record.

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.

Preserved records of tooth–bone interactions, known as tooth marks, can yield a wealth of information regarding organismal behavior and ecology. For this reason, workers in a wide range of disciplines, but particularly paleontology, have inspected and interpreted these features for decades. Although previous studies have gleaned invaluable insights, they have also described tooth marks using terminological frameworks that have been incompletely defined, have incorporated behavioral hypotheses in definitions, and/or have been inconsistently applied. To address these problems, we introduce the category-modifier (CM) system, the first system to both sort tooth marks into clearly defined main categories and use descriptive modifiers to characterize their appearance more precisely. The CM system is designed to apply to a wide range of vertebrates, to enable comparisons across disciplines and studies, and to help researchers keep their investigations into behavioral hypotheses free of circular reasoning.

The trace fossil record provides important insights into the evolution of early animals during the Ediacaran/Cambrian transition, with changes in ichnodiversity through time and between environments informing on the diversification of major body plans, behaviors, and niches. To quantify variation in the diversity of trace fossils across this critical interval, we propose a measure of trace fossil dissimilarity (ichnodissimilarity) based on vector calculation. Furthermore, by comparing discrepancies between the angular bisector and mean vector of two sets of vectorized fossil data, we are able to weigh the relative contribution of increases and decreases in the variation of occurrences of taxa. We used this metric to analyze an expansive dataset of Ediacaran/Cambrian trace fossils. The results allowed us to quantify the diversification of traces across this transition, informing on the timing of first appearance of different behaviors (e.g., foraging, grazing, and resting) and functional groups. By interpreting the results in the context of environmental changes and advancements in motility and sensory capabilities, we were able to pinpoint the onset and sequence of the Fortunian diversification event, Cambrian information revolution, and agronomic revolution, shedding light on the evolution of organismal body plans, behaviors, and locomotion during the Ediacaran/Cambrian transition. We identified two phases of origination and expansion during the divergence of early animal traces. Furthermore, by analyzing shallow- and deep-marine trace fossils, we were able to uncover evidence for a more rapid diversification of traces in shallow-marine environments, with progressive niche partitioning through the Ediacaran to Cambrian.

The fossil record offers important opportunities to reconstruct plant community response to past disturbance events. Yet reconstructions are hindered by limited empirical evidence of successional variation in functional traits measurable on fossil leaves, including leaf morphology and δ13C. In addition, the role the leaf economic spectrum (LES) plays across succession within temperate deciduous forests is unresolved. Finally, it is unclear to what degree disturbance confounds the leaf morphology–climate relationships utilized in paleoclimate proxies.

We utilize a chronosequence spanning forest stands varied by time since logging (4, 21, 44, and 94 years old) and one old-growth stand in North Carolina. Leaf traits of woody non-monocot angiosperm (WNMA) leaves, including all trees and prominent understory plants, were measured to document patterns relating to the LES (e.g., leaf mass per area [LMA]), patterns of leaf morphology and δ13C, and their confounding influence on climatic estimates using the digital leaf physiognomy proxy.

LMA increased across succession among trees, driven by variation in both leaf thickness and leaf density, supporting the role of the LES. The petiole metric (PM), which is biomechanically linked to LMA, increased across succession among trees as hypothesized, as did the proportion of entire-margined leaves and, among tree dominants, leaf margin complexity. Measures of diversity (morphological and species richness, δ13C, and LMA variance) for all WNMAs were often highest in the old-growth stand, reflecting structural and niche complexity, yet peaked in mid-succession among trees, reflecting a mixing of ecological strategies. Other leaf traits had complicated or subtle trends across succession that were difficult to reconcile and tie to function. Changes in leaf morphology across succession did not strongly confound the accuracy of paleoclimate reconstructions. Successional patterns of this study importantly highlight the utility of PM, leaf margin, and leaf morphological richness in interpreting successional dynamics from fossil leaf assemblages sourced from temperate deciduous forests.

Geometric morphometrics facilitates the quantification and visualization of variation in shape and proportion through the comparison of homologous features. Eublastoidea, a Paleozoic echinoderm clade with a conservative body plan, is an ideal group for morphometric analysis, because their plate junctions are homologous and identifiable on all species. Eublastoids have previously been grouped taxonomically by generalized shape types (e.g., globose). These shapes are often used in taxonomic descriptions and as characters in phylogenetic analyses. The underlying homology of these broad shape types has never been explored. Herein we apply the first comprehensive use of three-dimensional geometric morphometrics (3D GMM) on fossil echinoderms to investigate taxonomic assignments, temporal distribution, and whether the varying proportions of skeletal elements that produce the gross thecal morphology are distinguishable. Taxonomic assignments specifically at the ordinal and family levels show varying amounts of overlap in morphospace, suggesting that many assignments may not be reevaluated. Our results suggest that none of the generalized shape types are distinct in morphospace and, therefore, likely do not capture the homologous changes in taxa. The plate circlet ratios showed trends specifically relating to the deltoid plate circlet, which has the most variability. We reanalyzed previous work and subsetted our data to be more comparable and found that there are key differences between methodologies and landmarks that will require future evaluation. Applying modern technological methods to previously explored questions allows for an updated understanding of this important fossil clade and provides a framework for others to assess fossil clades in a similar manner.

Fossil data are subject to inherent biological, geologic, and anthropogenic filters that can distort our interpretations of ancient life and environments. The inevitable presence of incomplete fossils thus requires a holistic assessment of how to navigate the downstream effects of bias on our ability to accurately reconstruct aspects of biology in deep time. In particular, we must assess how biases affect our capacity to infer evolutionary relationships, which are essential to analyses of diversification, paleobiogeography, and biostratigraphy in Earth history. In this study, we use an established completeness metric to quantify the effects of taphonomic filters on the amount of phylogenetic information available in the fossil record of 795 extinct squamate (e.g., lizards, snakes, amphisbaenians, and mosasaurs) species spanning 242 Myr of geologic time. This study found no meaningful relationship between spatiotemporal sampling intensity and fossil record completeness. Instead, major differences in squamate fossil record completeness stem from a combination of anatomy/body size and affinities of different squamate groups to specific lithologies and depositional environments. These results reveal that naturally occurring processes create structural megabiases that filter anatomical and phylogenetic data in the squamate fossil record, while anthropogenic processes play a secondary role.

The body armor of ankylosaurians is a unique morphological feature among dinosaurs. While ankylosaurian body armor has been studied for decades, paleohistological analyses have only started to uncover the details of its function. Yet there has been an overall bias toward sampling ankylosaurian remains from the Northern Hemisphere, with limited quantitative studies on the morphological and functional evolution of the osteoderms composing their body armor. Here, we describe new ankylosaurian materials recovered from the Late Cretaceous of Antarctica that, in combination with data compiled from the literature, reveal new insights into the evolution of the ankylosaurian body armor. Based on histological microstructure and phylogenetic results, the new Antarctic material can be assigned to Nodosauridae. This group shares the absence/poor development of their osteodermal basal cortex and highly ordered sets of orthogonal structural fibers in the superficial cortex. Our morphospace analyses indicate that large morphological diversity is observed among both nodosaurids and ankylosaurids, but osteoderms became more functionally specialized in late-diverging nodosaurids. Besides acting as effective protection against predation, osteoderms also exhibit highly ordered structural fibers in nodosaurids, enabling a decrease in cortical bone thickness (as in titanosaurs), which could have been co-opted for secondary functions, such as calcium remobilization for physiological balance. The latter may have played a key role in nodosaurid colonization of high-latitude environments, such as Antarctica and the Arctic Circle.

Despite advances in understanding planktonic foraminifera environmental interactions, their role as prey remains elusive, often inferred from indirect evidence such as drill holes. Bioerosional traces offer valuable insights into fossil assemblages, although knowledge for planktonic foraminifera remains limited compared with benthic species. This study addresses this gap by analyzing bioerosional site selectivity in late Quaternary planktonic foraminifera from the western South Atlantic. We examined 2588 specimens from eight species to map trace patterns using kernel density estimation, sector-based, and hotspot mapping approaches. Drilling traces were located, transposed to graphical representations, and transformed into x,y coordinates. We analyzed specimen frequency per trace quantity and trace frequency, sectoring them per chamber and test regions. Correspondence analysis and exact test of goodness of fit assessed groupings among the species and preferential regions. Frequencies revealed that spinose species had more multiple-drilled specimens than non-spinose ones. Bioerosional traces were prevalent in the final whorl, decreasing toward earlier chambers. However, when normalized by surface area, the penultimate whorl had higher trace frequencies, particularly for spinose species, while the ultimate whorl had higher trace density for some non-spinose ones. Spinose species are preferentially drilled in the early chambers, likely due to their thinner walls. Thus, bioeroders prioritize regions with a higher cost–benefit ratio, which is evident in the prevalence of successful–failed traces in early chambers of spinose species, but not in thicker-walled, non-spinose ones. Our study reveals distinct bioerosion patterns, highlighting strategic site selectivity and suggesting that morphological differences between spinose and non-spinose species contribute to varying vulnerability to bioerosion.

The spatial distribution of in situ sessile organisms, including those from the fossil record, provides information about life histories, such as possible dispersal and/or settlement mechanisms, and how taxa interact with one another and their local environments. At Nilpena Ediacara National Park (NENP), South Australia, the exquisite preservation and excavation of 33 fossiliferous bedding planes from the Ediacara Member of the Rawnsley Quartzite reveals in situ communities of the Ediacara Biota. Here, the spatial distributions of three relatively common taxa, Tribrachidium, Rugoconites, and Obamus, occurring on excavated surfaces were analyzed using spatial point pattern analysis. Tribrachidium have a variable spatial distribution, implying that settlement or post-settlement conditions/preferences had an effect on populations. Rugoconites display aggregation, possibly related to their reproductive methods in combination with settlement location availability at the time of dispersal and/or settlement. Additionally, post-settlement environmental controls could have affected Rugoconites on other surfaces, resulting in lower populations and densities. Both Tribrachidium and Rugoconites also commonly occur as individuals or in low numbers on a number of beds, thus constraining possible reproductive strategies and environmental/substrate preferences. The distribution of Obamus is consistent with selective settlement, aggregating near conspecifics and on substrates of mature microbial mat. This dispersal process is the first example of substrate-selective dispersal among the Ediacara Biota, thus making Obamus similar to numerous modern sessile invertebrates with similar dispersal and settlement strategies.

In The Structure of Evolutionary Theory, Stephen Jay Gould observed that the theory of punctuated equilibria formed “the coordinating centerpiece” of his work in evolutionary biology. It occupied this position because it bridged several themes in Gould’s thought, including the necessity of understanding evolution in a hierarchical context and a critique of the adaptationist program in evolutionary biology. Yet this assessment concealed a historical puzzle. The puzzle arose from the fact that the Gould of “Eldredge and Gould (1972)” held several commitments that the older Gould did not. These included a preference for adaptationist explanations and, perhaps more surprising, a commitment to the central importance of “biological improvement” in the history of life. So, how did punctuated equilibria come to play a coordinating role within a view of evolution that differed starkly from the one Gould held in 1972? And why did it only begin to play this role after 1977? This article answers these questions, focusing on the aims of Gould’s early research program and its transformation in response to external stimuli. In so doing, it illuminates an important and frequently misunderstood episode in the history of paleobiology.

The Cretaceous/Paleogene (K/Pg) mass extinction was a pivotal event in Earth history, the latest among five mass extinctions that devastated marine and terrestrial life. Whereas much research has focused on the global demise of dominant vertebrate groups, less is known about changes among plant communities during the K/Pg mass extinction. This study investigates a suite of 11 floral assemblages leading up to and across the K/Pg boundary in northeastern Montana constrained within a well-resolved chronostratigraphic framework. We evaluate the impact of the mass extinction on local plant communities as well as the timing of post-K/Pg recovery. Our results indicate that taxonomic composition changed significantly from the Late Cretaceous to Paleocene; we estimate that 63% of latest-Cretaceous plant taxa disappeared across the K/Pg boundary, on par with other records from North America. Overall, taxonomic richness dropped by ~23–33% from the Late Cretaceous to the Paleocene, a moderate decline compared with other plant records from this time. However, richness returned to Late Cretaceous levels within 900 kyr after the K/Pg boundary, significantly faster than observed elsewhere. We find no evidence that these results are due to preservational bias (i.e., differences in depositional environment) and instead interpret a dramatic effect of the K/Pg mass extinction on plant diversity and ecology. Overall, plant communities experienced major restructuring, that is, changes in relative abundance and unseating of dominant groups during the K/Pg mass extinction, even though no major (e.g., family-level) plant groups went extinct and communities in Montana quickly recovered in terms of taxonomic diversity. These results have direct bearing on our understanding of vegetation change during diversity crises, the differing responses of plant groups (e.g., angiosperms vs. gymnosperms), and spatial variation in extinction and recovery timing.

Drilling predation is a common reason for mortality of benthic mollusks but did not become common until the late Mesozoic. The scarcity of drill holes in the early Mesozoic fossil record limits our understanding of the evolution of drilling behavior and its role on shaping early Mesozoic marine communities. Here, we use drilling traces on several bivalve taxa from the Lower Jurassic (Pliensbachian) marine soft-bottom deposits in northern Germany to explore behavioral patterns of the predator (e.g., site selectivity, change in site-selective behavior with age). Although none of the known drilling gastropod groups existed in the Pliensbachian, including the studied localities, the drill-hole morphology suggests that the predator was probably a gastropod. The ecology and identity of the target prey changes from a diverse array of epifaunal to infaunal taxa in older deposits to focus on a single, large, deep infaunal taxon, Gresslya intermedia, in younger deposits, suggesting a potential trend in prey selectivity over time. Spatial point pattern analysis of traces (SPPAT) reveals an aggregated pattern of drill holes on Gresslya, suggesting strong selectivity in drill-hole location. Drilling on a single large infaunal taxon and site selectivity are common patterns also inferred previously from the drilled deep infaunal Eothyasira from the Pliensbachian of southern Germany. In addition to the scarcity of predators, the highly specialized behavior of the early drilling predators, including strong prey selectivity in terms of prey identity and life habit, can partly explain the rarity of the early Mesozoic drill holes.

We analyzed the oxygen isotope composition of biogenic apatite phosphate (δ18Op) in fossil tooth enameloid to investigate the paleoecology of Late Cretaceous sharks in the Gulf Coastal Plain of Alabama, USA. We analyzed six different shark taxa from both the Mooreville Chalk and the Blufftown Formation. We compared shark δ18Op with the δ18Op of a co-occurring poikilothermic bony fish Enchodus petrosus as a reference for ambient conditions. Enchodus petrosus tooth enamel δ18Op values are similar between formations (21.3‰ and 21.4‰ Vienna Standard Mean Ocean Water [VSMOW], respectively), suggesting minimal differences in water δ18O between formations. Most shark taxa in this study are characterized by δ18Op values that overlap with E. petrosus values, indicating they likely lived in similar habitats and were also poikilothermic. Ptychodus mortoni and Cretoxyrhina mantelli exhibit significantly lower δ18Op values than co-occurring E. petrosus (P. mortoni δ18Op is 19.1‰ VSMOW in the Mooreville Chalk; C mantelli δ18Op is 20.2‰ VSMOW in the Mooreville Chalk and 18.1‰ VSMOW in the Blufftown Formation). Excursions into brackish or freshwater habitats and thermal water-depth gradients are unlikely explanations for the lower P. mortoni and C. mantelli δ18Op values. The low P. mortoni δ18Op value is best explained by higher body temperature relative to surrounding temperatures due to active heating (e.g., mesothermy) or passive heating due to its large body size (e.g., gigantothermy). The low C. mantelli δ18Op values are best explained by a combination of mesothermy (e.g., active heating) and migration (e.g., from the Western Interior Seaway, low-latitude warmer waters, or the paleo–Gulf Stream), supporting the hypothesis that mesothermy evolved in lamniform shark taxa during the Late Cretaceous. If the anomalous P. mortoni δ18Op values are also driven by active thermoregulation, this suggests that mesothermy evolved independently in multiple families of Late Cretaceous sharks.

Variation in observed global generic richness over the Phanerozoic must be partly explained by changes in the numbers of fossils and their geographic spread over time. The influence of sampling intensity (i.e., the number of samples) has been well addressed, but the extent to which the geographic distribution of samples might influence recovered biodiversity is comparatively unknown. To investigate this question, we create models of genus richness through time by resampling the same occurrence dataset of modern global biodiversity using spatially explicit sampling intensities defined by the paleo-coordinates of fossil occurrences from successive time intervals. Our steady-state null model explains about half of observed change in uncorrected fossil diversity and a quarter of variation in sampling-standardized diversity estimates. The inclusion in linear models of two additional explanatory variables associated with the spatial array of fossil data (absolute latitudinal range of occurrences, percentage of occurrences from shallow environments) and a Cenozoic step increases the accuracy of steady-state models, accounting for 67% of variation in sampling-standardized estimates and more than one-third of the variation in first differences. Our results make clear that the spatial distribution of samples is at least as important as numerical sampling intensity in determining the trajectory of recovered fossil biodiversity through time and caution against the overinterpretation of both the variation and the trend that emerge from analyses of global Phanerozoic diversity.

Conodont elements have high rates of morphological evolution, but the drivers of this disparity are debated. Positive allometric relationships between dimensions of food-processing surfaces and entire P1 elements have been used to argue that these elements performed mechanical digestion. If involved in food processing, the surface of the element should grow at a rate proportional to the increase in energy requirements of the animal. This inference of function relies on the assumption that the energy requirements of the animal grew faster (≅ mass0.75) than the tooth area (≅ mass0.67). We reevaluate this assumption based on metabolic rates across animals and calculate the allometry in platform-bearing P1 elements of Late Triassic co-occurring taxa, Metapolygnathus communisti and Epigondolella rigoi, using 3D models of ontogenetic series. Positive allometry is found in platform and element dimensions in both species, supporting a grasping-tooth hypothesis, based on the assumption that metabolic rate in conodonts scaled with body mass similarly to that in fish and ectotherms. We also calculate the curvature of the P1 platform surface using the Dirichlet normal energy (DNE) as a proxy for diet. DNE values increase with body mass, supporting the assumption that conodont metabolic rates increased faster than mass0.67. We finally find that adults in both taxa differ in their food bases, which supports trophic diversification as an important driver of the remarkable disparity of conodont elements.

The hyoid apparatus is essential for underwater feeding in marine tetrapods, but it is unclear whether this complex has evolved as convergently as other traits, such as dentition or locomotion. Here we compare the ossified hyoid elements in ophthalmosaurid ichthyosaurs and odontocete cetaceans, two groups with an overall similar body shape, to understand whether the hyoid elements show any signs of convergence in the context of feeding. We examined three types of data (size, morphology, and internal bone microstructure) in ophthalmosaurid and odontocete taxa in which these elements are preserved. Our data show that ichthyosaurs never experienced a shift in feeding mode, which might indicate that their hyoid apparatus never adapted to suction feeding. Also, the internal microstructure of the two animal groups differs; where the odontocetes have an overall less compact structure, ophthalmosaurid ichthyosaurs have cancellous inner cones in an outer, more compact sheath. These differences are likely explained as biomechanical adaptations to different feeding modes. Thus, the hyoid changed less and acted more as a constraint for feeding innovation in ichthyosaurs compared with cetaceans, and through a much longer time span (more than 150 Myr).