Abstract Galeaspids are an extinct group of jawless fishes from the Silurian–Devonian of China and northern Vietnam that are key to understanding the origin of vertebrate anatomical innovations. A new eugaleaspid, Bataspis crux gen. et. sp. nov., is described based on fossil material from the Lochkovian (Early Devonian) Xishancun Formation of Qujing, Yunnan, China. Bataspis crux possesses a suite of unusual features, especially its bat‐wing‐like cornual processes that are seamlessly integrated with a brim‐like rostral margin without a rostral process, constituting a unique morphology for galeaspids. Maximum parsimony, maximum likelihood and Bayesian phylogenetic inference all support membership in the family Tridensaspidae. We employed computational fluid dynamics to infer the hydrodynamic properties of the headshield of B. crux . Our analysis reveals that this species achieves an exceptionally high lift‐to‐drag ratio; the highest recorded among known galeaspids. This remarkable efficiency stems from its low drag across various angles of attack, coupled with passive lift generation through the exploitation of the Bernoulli effect by the airfoil cross‐section of the cornual processes. This suggests that the species was an effective gliding cruiser, outperforming not only galeaspids but also other stem gnathostomes, such as osteostracans and pteraspidomorphs. These results provide new insights into our understanding of the evolution of Tridensaspidae, the ecological habits of stem gnathostomes and convergence in the evolutionary assembly of the gnathostome bodyplan.
An enigmatic, yellowish-brown, variably branched organic-walled microfossil (palynomorph) marks the Late Glacial Maximum of Upper Pleistocene sediments in the Marmara Sea. This taxon, previously called a Multiplicisphaeridium-type acritarch, a putative algal cyst, or a possible chytrid fungus, virtually disappears at the end of the Ponto-Caspian lacustrine phase, making it a valuable marker for regional ecostratigraphic correlation. However, uncertainty surrounding its biological affinity limits interpretations of its taxonomy, palaeoecology, evolutionary history, and broader geographic significance. We document the morphology and variability of well-preserved cf. Multiplicisphaeridium specimens from Marmara and Black Sea sediment cores using interference light microscopy and scanning electron microscopy. Detailed morphological comparisons with visually similar acritarchs, chytrids and dinoflagellates indicate a plausible, though non-definitive, affinity with chytrid fungi and exclude pre-Quaternary sedimentary reworking. Compositional analyses using attenuated total reflection Fourier transform infrared microspectroscopy reveal a close biomacromolecular match between cf. Multiplicisphaeridium and co-occurring chytrid sporangia, including evidence of wall melanization potentially characteristic of chytrids but distinct from other fungal clades. Additional comparative analyses of sporangia from extant marine Rhizophydium further contextualize chytrid wall taphonomy. The combined morphological and molecular evidence favours a chytrid-like affinity and demonstrates distinction from true Multiplicisphaeridium acritarchs, but does not justify assignment to a known chytrid lineage (extant Arkaya is identified as a potential close analogue). We therefore erect a new genus and species within the Acritarcha, Palaeoarkaya similis, and discuss its potential significance in low-salinity glacial palaeoenvironments. This integrative morpho-molecular approach confirms earlier evidence of possible fungal affinity among acritarchs.
Abstract The cranium of sauropodomorph dinosaurs is relatively small and diverse in shape. However, the cranial topology of sauropodomorphs has not previously been investigated. The distinct pattern of physical interactions (joints) among the elements (bones) of an anatomical system (cranium) reveals information about its morphology, leading to a better understanding of the evolutionary radiation of the clade. Namely, applying anatomical network analysis to the study of sauropodomorph cranial topology allows us to assess whether a given morphological change is more likely to be driven either by functional adaptation or by spatial constraints. Networks of the crania of a sample of 14 sauropodomorph species were built, each comprising roughly 40 nodes and over 100 edges, and analysed at two scales: the individual bones (locally) and the cranium in its entirety (globally). Locally, the results suggest that, in most species, the bones of the braincase and the maxilla were especially susceptible to sustaining and enforcing major spatial constraints, which probably channelled their morphological evolution. Globally, Williston's Law is not supported in Sauropodomorpha, although a discrete topological discrimination between non‐sauropod and macronarian sauropodomorphs based on the integration of their cranium is observed. Moreover, the community structure of the sauropodomorph cranium follows, most notably, a rostrocaudal modular pattern compatible with their overall morphogenetic separation into the snout and the braincase.
New post-embryonic specimens and the first known embryos of Octapyrgites elongatus, a medusozoan cnidarian in the family Olivooidae, are described from Member 5 of the Yanjiahe Formation (Cambrian Stage 2) in western Hubei Province, South China. This discovery extends the embryological record of olivooids beyond the Kuanchuanpu biota and from the Fortunian Stage to Cambrian Stage 2. Micro-CT scans of three embryos revealed internal anatomical structures, including relict soft tissue and stacked sets of four and eight embryonic oral lobes, with the four-lobed set situated closest to the oral pole. Together, available specimens of O. elongatus record a mostly complete developmental cycle extending from the early organogenesis stage to hatchling specimens showing 12 annulations in the aboral portion of the theca. Co-occurring, morphologically similar spheroidal specimens probably represent the earlier cleavage, blastula, or gastrula stages. Embryos of O. elongatus are relatively large, averaging 720 mu m long, though many embryos have undergone diagenetic shrinkage and deformation. As in other olivooids, development was direct, with adoral migration of the embryonic oral lobes. The early ontogeny of O. elongatus is most similar to that of Quadrapyrgites quadratacris, further suggesting that Octapyrgites and Quadrapyrgites, both of which exhibit tetraradial symmetry, were more closely related to each other phylogenetically than either was to Olivooides or to the three other, pentaradially symmetrical olivooid genera.
Body size evolution is commonly associated with climate change. For example, birds and mammals have been found to decrease in size with anthropogenic global warming. Recent studies have inferred distinct shifts in climatic niche preferences among the three major dinosaur clades. Following the Early Jurassic Toarcian extinction event (Jenkyns Event), sauropods increasingly occupied warmer and drier environments, while theropods shifted toward cooler and wetter climates. Ornithischians showed a similar pattern to theropods, but much later, coinciding with the Late Cretaceous Cenomanian/Turonian boundary. We apply phylogenetic comparative methods to test whether shifts in preferred climatic niches are coupled with dinosaur body size evolution. We find no support for a correlation between body size and local palaeotemperature, seasonality, or mean annual precipitation (MAP) among species in any dinosaur clade, before or after shifts in preferred climatic niches. With this original dataset, we find that larger eusauropod body sizes are weakly correlated with lower MAP after the Jenkyns Event. However, this trend is not recovered when using a larger and more recent dataset of eusauropods, demonstrating that the strength of such climate-size relationships is subject to sampling intensity. Our findings highlight the complex role of climate on body size evolution and how the detection of macroevolutionary patterns is influenced by sample size.
The Triassic was a unique time for beak evolution, as seen in a wide diversity of terrestrial tetrapods. Beaks were present in dicynodont synapsid survivors of the Permo-Triassic mass extinction event (PTME) and evolved independently several times in archosauromorphs and their relatives. Here, we explore the morpho-functional characteristics of the first beaked jaws as well as the roles of these beaks, using a combination of geometric and functional morphometric analyses on 2D material. This revealed the functional capabilities of these jaws, and enabled inferences on the trophic relationships of these early beaked tetrapods. Dicynodont morphospace occupation remained largely stable through the PTME, while newly evolved beaked archelosaurs (= archosaurs + turtles) occupied distinct areas of morphospace. Archelosaur and dicynodont beaks were functionally different, with archelosaurs exhibiting greater morpho-functional variation and further differentiation between subclades. Clear differences in jaw and beak shape and function indicate divergent feeding behaviours that are consistent with niche partitioning. We further identify three functional groups (snippers, shearers, and slicers) that reflect these different feeding specializations. Our study elucidates patterns of divergence along morpho-functional and phylogenetic trajectories that are rooted in the early evolution of beaked clades. While united by the convergent development of the specialized oral structure, these lineages evolved independent feeding strategies that highlight the strength of ecological pressures on morpho-functional evolution.
Symbiosis impacts ecological interactions and evolutionary innovations, yet, direct evidence of host-symbiont dynamics is rarely preserved in the fossil record. The study of the Middle Jurassic hydroid Protulophila gestroi bioclaustrated within the tubes of serpulid Propomatoceros lumbricalis provides valuable insights into syn vivo interactions and palaeoecological conditions that shaped this symbiosis. Specimens from four Bajocian-Callovian localities derive from different palaeoenvironments of the Polish Basin. Hydroids are preserved in the external tube portions as small apertures surrounded by bulges formed during bioclaustration, reflecting skeletal overgrowth by the serpulid host. High-resolution micro-CT imaging enabled reconstruction of internal hydroid morphology and morphometric quantification. The preserved traces consist of thin, branching and anastomosing stolons and elongated cavities corresponding to polyp chambers. Comparative analysis within individual serpulid specimens and across environments reveals strong host-symbiont interdependence; external aperture morphology correlates with the depth of colony incorporation, indicating significant influence of host biomineralization. Variation among hosts suggests that, besides host-symbiont dynamics, environmental and behavioural factors such as food availability and water dynamics also contributed to shaping these relationships. These findings provide rare, direct evidence of host-regulated symbiosis in deep time, demonstrating the complex physiological interdependence in Mesozoic mutualistic relationships.
Recent work has suggested that the presence of extraoral soft tissues ('lips'), in the form of labial scales in theropod dinosaurs, could be inferred based on: anteroposteriorly distributed foramina in the rostral bones, similar to extant lepidosaurs; vertically projected teeth; uniform enamel thickness in maxillary teeth; and an allometric relation between skull length and maxillary crown height. Here, we review the current state of knowledge on the presence of lips in saurischian dinosaurs and further contribute to the debate by inferring and discussing their presence in Triassic archosauromorphs, particularly those from southern Brazil, using the same methodological approach. Our results support the hypothesis that the lipped condition represents the plesiomorphic state in Sauropsida. Non-theropod Triassic saurischians and pseudosuchians exhibit a foraminal distribution similar to that of theropods and extant lepidosaurs. Histological thin sections reveal a uniform enamel thickness on both labial and lingual sides of functional and shed tooth crowns, and the dentine shows no evidence of wear, contrasting with the condition in crocodilian teeth. Additionally, our regression analysis supports an allometric trend in which increased skull length correlates with increased maxillary crown height in Theropoda, Sauropodomorpha, Herrerasauria and Pseudosuchia. We also infer and discuss the presence of a mandibular gap in Prestosuchus, as well as the occurrence of lips in specialized taxa from the clades Theropoda, Ornithosuchidae, Phytosauria and Proterosuchidae, based on convergent rostral features shared with extant lepidosaurs and actinopterygians. Furthermore, we examine the presence of both rhamphotheca and labial scales across the clades Silesauridae, Lagerpetidae and Rhynchosauria.
The extinct crocodyliform Diplocynodon represents one of the best sampled tetrapods of the Cenozoic era. Endemic to Europe, the fossil record of the taxon spans from the upper Paleocene to the Middle Miocene, documented by a vast number of occurrences comprising both exceptionally well-preserved and fragmentary material. The clade is considered to have reached a peak of diversity during the Eocene, implying allopatric or possibly even sympatric lineage divergence. Based on a critical review and first-hand examination of Diplocynodon species, we present the first comprehensive taxonomic revision of the group since its inclusion in modern phylogenetic works. We hereby demonstrate that the diagnoses of several species often include shared and/or irreproducible characters, hampering specific delimitation. This taxonomic revision of Diplocynodon spp. presents amended diagnoses for the genus and the species, and confirms 9 valid taxa out of the 11 previously published, recognizing two additional species among an updated list of dubious species. Furthermore, we quantitatively and qualitatively review the state of the published fossil record of Diplocynodon, based on two openly available databases, and comment on the state of the art of the taxon record with respect to recommended taxonomic practices.
Praearcturus gigas Woodward is a large arthropod of disputed affinity from the fluvial St Maughans Formation (Lower Devonian, Lochkovian) of the Old Red Sandstone of England and Wales. Originally described as an isopod in the nineteenth century, and subsequently compared to various arthropod groups, it was re-described with limited illustration as a gigantic scorpion in the 1980s. Recently, this interpretation has been challenged, warranting a modern revision of the material. Illustrating P. gigas with camera lucida drawings, light photography and tomographic data, we present a re-description of the type material and assign several other specimens from the same formation to this taxon, thence identifying Brontoscorpio anglicus Kjellesvig-Waering and Bennettarthra annwnensis Fayers et al. as junior synonyms of P. gigas. Several characters supporting a scorpion affinity are present in P. gigas, including large pedipalps with a fixed and movable finger, a stridulatory surface on one of the coxae, and an elongate subtriangular sternum morphology shared with the unambiguous Silurian scorpion Eramoscorpius brucensis Waddington et al. (Wenlock, Canada). Uniquely among scorpions, P. gigas has lateral epimera on the mesosomal tergites, and combined with the fluvial environment in which the fossils are preserved, we suggest that P. gigas may have been aquatic or amphibious. Finally, we review the evidence for scorpion gigantism and discuss the evolutionary context of a large arachnid predator in the Early Devonian.
Predaceous diving beetles (Dytiscidae) are among the best-known and most extensively studied beetle clades. Their fossil record, however, remains surprisingly sparse and uneven, failing to reflect their broad extant diversity. Consequently, the study of their evolutionary history, leveraging the fossil record, particularly their diversification dynamics, has often been limited. To overcome this issue, we used the Bayesian Brownian bridge model, which is particularly suited for clades with incomplete fossil records. Although primarily designed to estimate clade origination time, the model can also be applied to infer origination and extinction dynamics while accounting for bias due to uneven sampling. Using this model and a curated dataset of fossil occurrences covering 41 genera and 155 species of Dytiscidae, we estimated the timing of the family's origination and of each genus represented in its fossil record. Our results show an origin of Dytiscidae either during the Late Triassic (c. 220 Ma) or during the Early Jurassic (c. 190 Ma). Although these estimates are consistent with most recent time-calibrated phylogenies, they provide additional clues for an ancient origin of the family. Following their origin, Dytiscidae diversified across the different geological epochs, probably in response to tectonic shifts and climate oscillations.
Notosuchian crocodylomorphs were predominantly active terrestrial predators, exhibiting a wide range of ecomorphological specializations and body sizes. Given that body size plays an important role in the life history of vertebrates, its accurate estimation for notosuchians is crucial for understanding macroevolutionary and macroecological patterns in the group. Yet, reconstructing body size of fossil species with no living representatives is challenging, as demonstrated previously for Notosuchia, as well as other taxonomic groups. Here, we estimated the total body length of 40 Cretaceous-Cenozoic notosuchian species using a phylogenetic Bayesian inference approach that accounts for non-independence of taxa, based on cranial and femoral measurements from near-complete crocodylomorph specimens. Our results reveal notable discrepancies between estimates based on crania and femora, with skull length providing more robust estimates. We suggest that femoral length is more strongly influenced by factors such as locomotion, limb posture, and ecological habitat, all of which vary across Notosuchia (and Crocodylomorpha more broadly). Nevertheless, the sizes of both skeletal regions are significantly correlated with total body length in notosuchians. Larger body sizes are typically associated with a more semi-aquatic lifestyle, probably due to selective pressures associated with this ecology. Our findings also suggest that notosuchians from freshwater habitats and with less specialized diets were less affected by the Cretaceous-Palaeogene mass extinction event, allowing some lineages to persist and ultimately thrive in its aftermath.
The Pseudosuchia (Diapsida, Archosauria) arose during the Early Triassic and were the dominant large to medium-sized tetrapods in continental ecosystems until the Triassic-Jurassic extinction. Despite this important palaeoecological role, the group remains poorly examined. Here, we report several palaeobiological, palaeoecological and phylogenetic implications based on the bone histology of appendicular elements of seven species of non-crocodylomorph Pseudosuchia from South America, and provide a review of the current state of the osteohistological research on this group. Saurosuchus galilei (Paracrocodylomorpha, Loricata) and Sillosuchus longicervix (Paracrocodylomorpha, Poposauroidea) exhibit fibrolamellar complexes, showing extremely rapid growth. Similarly, Aetobarbakinoides brasiliensis (Aetosauria) and Gracilisuchus stipanicicorum (Gracilisuchidae) display woven-fibred bone, indicative of fast growth. However, Aetosaourides scagliai (Aetosauria) and Tarjadia ruthae (Erpetosuchidae) developed both woven-fibred and parallel fibred bone, which implies an intermediate or moderate growth rate. Finally, Riojasuchus tenuisceps (Ornithosuchidae) records parallel-fibred bone mostly, marking a slower growth rate. Nevertheless, when compared with other pseudosuchians worldwide, this diversity in growth rate does not indicate a reduction in growth rate within the lineage from stem towards crown Pseudosuchia (i.e. a phylogenetic signal). Neither does it correspond with estimated global palaeoclimatic patterns but instead seems to respond to more local environmental influences (e.g. seasonality) and to intrinsic physiological issues. In general, the diversity seen in the growth dynamics of the Triassic non-crocodylomorph Pseudosuchia from South America is similar to that reported for North America and Europe.
Lauraceae are a tropical-subtropical angiosperm family that exhibit significant diversity and a rich fossil record, primarily of leaves found worldwide from the Cretaceous to the present. However, the taxonomic placement of many fossil leaves remains uncertain because of morphological convergence and limited variation in leaf characters among both extant and fossil species. We analysed the evolution and systematic relevance of 13 leaf architecture characters in extant Lauraceae using ancestral character state reconstructions (maximum likelihood) and phylogenetic signal analysis. Our results indicate that these characters originated multiple times within the family and had a significant phylogenetic signal. Although the multiple character origins cannot define higher taxonomic levels, their phylogenetic signal indicates that these characters, in combination, are a useful diagnostic guide for identifying members at the family level. This is relevant to the fossil record because it helps explain morphological convergence, such as in Cinnamomum-type leaves and the genus Laurophyllum. They are also useful for relating Cretaceous fossils, a period marked by morphological complexity and the coexistence of stem and crown groups. A diagnostic guide may help identify crown group members, even when they exhibit unique, possibly automorphic, characters. Finally, the morphology of the last common ancestor is debatable due to the Cretaceous morphological mosaic, particularly for the lobed leaves. However, this will become clearer as the phylogenetic position of these Cretaceous fossils becomes better resolved. Although our findings are based on extant species, better-supported and clearly defined characters can help improve the integration of fossil data into phylogenetic systematics.
Iguanodontia (Dinosauria, Ornithischia) is a speciose group of herbivorous dinosaurs that include the famous genus Iguanodon, one of foundational members of the clade Dinosauria. Despite their very long history of research, several aspects of their systematic relationships and their evolutionary history remain somewhat nebulous. There is currently a lack of consensus between different phylogenetic matrices due mainly to: (1) undersampling of postcranial characters; and (2) the absence of several key taxa. We assembled a data matrix from pre-existing datasets, integrating our observations on several overlooked species (mainly from Europe) and extensively sampling cranial and postcranial characters, thereby creating one of the most complete datasets for iguanodontian dinosaurs to date. We performed a series of phylogenetic analyses, employing maximum parsimony and Bayesian inference, and an historical biogeographic analysis. Overall congruent topologies between the two methods recovered, for the first time, a new clade of high-sailed styracosternans here named Ouranosauria. We ran different Bayesian inference analyses, employing morphoclock and fossilized birth-death models. Some of the tip-dated analyses, indicated an Early to Middle Jurassic origin of Iguanodontia during a palaeoclimatically (hyperthermal) and palaeogeographically (continental fragmentation) dynamic context. According to this scenario, the Iguanodontian major radiation could be tracked back to the Pliensbachian-Toarcian, pre-dating by 16 million years the first ichnological evidence attributed to this clade. Furthermore, the diversification of all the major clades occurred by the Late Jurassic, then experienced local extinction events in different areas during the Early Cretaceous. Prior to the Jurassic-Cretaceous transition, iguanodontians spread globally.
Tommotiids are an enigmatic but important group of early Cambrian lophotrochozoans, characterized by a complex external skeleton (or scleritome) comprised of fused or cataphract organophosphatic sclerites produced by basal marginal accretion. Currently, tommotiids are informally subdivided into three main groups: the mobile, benthic camenellans that accreted a complex array of sclerites arranged in serial rows along the length of the body; and two sessile groups that include the tubiform eccentrothecimorphs and bimembrate caniculate tannuolinids, currently recognized as members of the Lophophorata. Here we undertake a detailed study of internal ultrastructure and surface ornamentation of partially fused tubular scleritomes and a wide range of isolated sclerite morphotypes of key early Cambrian eccentrothecimorph taxa from Australia. Comparisons are also made with the shell ultrastructure and ornamentation of the contemporaneous paterinate brachiopod Askepasma, along with other previously described paterinates and enigmatic stem group brachiopods. Mode of fusion between adjacent sclerites in the scleritomes of Kulparina rostrata and Eccentrotheca helenia is shown to be identical, consisting of a series interlocking dome and saddle features. New data also reveal that all Australian eccentrothecimorph sclerites possess first and second order organophosphatic laminations, distinctive penetrative polygonal structures (PPS), and surface ornament textures, which are also shared with Askepasma and other early Cambrian paterinates, reinforcing the close relationship between these taxa. In addition, the newly discovered scleritome of Kulparina rostrata is briefly described for the first time herein, providing further evidence that a tubular scleritome is a shared feature of eccentrothecimorphs.
The tetrapod water-land transition has been studied for more than a century, but questions about the locomotor function of early tetrapod limbs still remain. The limb and girdle skeletons of stem tetrapods are morphologically distinct from those of crown tetrapods, probably resulting in differences in range of motion and muscle leverage. To test hypotheses about their limb function, we built three-dimensional musculoskeletal models of the stem tetrapods Acanthostega (Devonian) and Pederpes (Carboniferous), and of an extant salamander and lizard for comparison. We predicted that the joints of stem tetrapods would not be able to accommodate the full range of movements used by extant tetrapods during terrestrial walking, and that stem tetrapods would have less muscle leverage for resisting vertical forces and for hindlimb-based propulsion. As expected, hip and shoulder mobility in the two stem tetrapods was incompatible with the kinematic patterns used by extant sprawling tetrapods. In contrast, their hip and shoulder depression muscle moment arms were similar to or greater than those of the crown tetrapods, and retraction moment arms were similar between the hip and shoulder in all four tetrapods, showing little evidence that the limbs of stem tetrapods were less adapted for weight support or HL-driven locomotion. However, the moment arm results were sensitive to methodological choices such as joint angles and normalization. Comparison with additional extinct and extant tetrapods with different locomotor strategies could clarify how muscle moment arms are related to limb mechanics and aquatic versus terrestrial locomotion.
Sauropods are the largest-known terrestrial animals, characterized by their columnar limbs and obligate quadrupedality. They are nested within Sauropodomorpha, a clade whose earliest representatives were, however, small bipeds. The early evolution of gigantism and quadrupedality within sauropodomorphs remains debated, since several non-sauropods reached large sizes before the emergence of the sauropod bauplan, and are frequently interpreted as quadrupedal. Recently, a study of sauropodomorph limb long bones highlighted a differential evolutionary pattern between the forelimb and hindlimb, with sauropod-related traits appearing abruptly in the former and gradually in the latter. However, conclusions were limited for the humerus by poor preservation of this bone in large non-sauropodan sauropodomorphs. We aimed to clarify how humeral morphology evolved with the emergence of the sauropod bauplan. Using 3D geometric morphometrics, we analysed humeral proximal and distal halves, adding numerous key but incomplete specimens. We show that humeral halves evolved differently: proximally, locomotor groups are overlapping, reflecting morphological similarities between those groups, whereas distally, quadrupedal sauropods are markedly distinct. This highlights a decoupled evolutionary pattern within the humerus itself, with sauropod-related traits appearing gradually proximally, and abruptly distally as previously found for the antebrachium. This congruence suggests the existence of a morphological module centred around the elbow. It corroborates that sauropodomorph forelimb evolution was more complex than a progressive transition towards the sauropod condition, questioning how quadrupedality was feasible in non-sauropods. Forelimb evolution may be regionalized around joints rather than bone elements, similarly to distantly-related mammalian groups, suggesting a more widespread trend in amniotes.
Sympatry of numerous predatory marine reptiles appears to be the rule rather than the exception in many Mesozoic formations, implying that these lineages are likely to have evolved some form of ecological partitioning. Many studies have focused on dental morphology as a proxy for the feeding habits of aquatic tetrapods, but much more ecological insight may be gained through simulations of the mechanical performance of craniomandibular elements. Here, we conducted the first, large-scale comparative study of marine reptile jaw biomechanics, applying muscle-driven finite element analyses (FEA) on a dataset of high-resolution three-dimensional models. Our study-system included mosasaurids and polycotylid plesiosaurians from the Santonian-Maastrichtian of the Western Interior Seaway (WIS), a vast inland sea that stretched longitudinally across North America during the Late Cretaceous. Muscle insertions were identified to reconstruct jaw adductor muscles and simulate respective muscle and bite forces. We simulated realistic muscle traction dynamics during biting, including simulations at multiple opening angles and bite locations. We recover clearly distinct biomechanical performances among the sample, notably between the slender-snouted mosasaurids (e.g. Clidastes) plus polycotylids, and the robust-jawed mosasaurids (e.g. Prognathodon). By integrating jaw length and other biomechanical metrics derived from our analyses, we provide strong support for differential biting mechanics among these marine predators, which doubtless influenced their ecological roles. Our results offer deeper insight into the feeding ecologies of Late Cretaceous marine reptiles, and provide a unified protocol to assess the role of feeding biomechanics in niche partitioning among sympatric marine reptiles from well-sampled regions.
The Silica Shale brachiopod, Paraspirifer bownockeri, of Ohio and Michigan, USA, preserves a unique window into Middle Devonian communities, as individuals hosted numerous epibionts. Herein, we use qualitative and quantitative methods to test hypotheses regarding the palaeoecology of these brachiopod hosts and their epibionts. We analysed the number and type of epibionts on the dorsal valve, ventral valve, hinge, and commissure of over 200 specimens. Using a variety of statistical techniques, we tested hypotheses regarding the relationships of these epibionts both to their host and to one another. We also produced 3D models of these specimens to explore hypotheses as to how epibiont colonization impacted host morphology. Finally, we compare our results to previous work on Silica Shale brachiopods. Our data show a correlation between shell morphology and epibiont placement that may indicate preferential placement in the water column or epibiont influence on host morphology. We found an average of 1.96 epibionts per host, with several significant correlations between co-occurring pairs. By applying these new data to previously published life position models and epibiont placement data, we reevaluated the life position of these brachiopods and found that the most likely position for these brachiopods in life would have been with the commissure 30-45 degrees angled above the sea floor. Our interpretation of the results differs from the original work on these brachiopods with regards to the epibiont relationships to one another, colonization patterns, and life position but supports more recent work evaluating spirifer life position and morphology.
