The osteology of the Late Triassic reptile Scleromochlus taylori from μCT data

Scleromochlus taylori is one of the most enigmatic members of the herpetofauna from the Lossiemouth Sandstone Formation (Upper Triassic) of Elgin (Moray, Scotland). For many years it was thought to be closely related to pterosaurs and dinosaurs, but the anatomy of this animal is difficult to interpret because of the notoriously poor preservation of the six available specimens, which comprise void space in the sandstone after the bones were destroyed by diagenesis. Historically, these fossils have been studied using physical molds, which provide only incomplete, and potentially distorted, information. Due to these uncertainties, interpretations of the anatomy, phylogenetic relationships, and paleobiology of Scleromochlus taylori have remained contentious. Here, we use microcomputed tomographic (μCT) techniques to redescribe and illustrate the osteology of Scleromochlus in detail, building upon a short redescription of keystone features of the anatomy that we recently published. We digitally visualize, describe, and figure previously inaccessible-and thus unaltered-portions of its skeleton, as well as providing new observations on the exposed parts of each specimen. This work reveals many novel features of the skull, mandible, trunk, tail, girdles, forelimb, and hindlimb (particularly of the manus, femur, and pes), demonstrating that historic molding techniques failed, in some cases, to accurately capture the anatomy of Scleromochlus. Our review sheds light on some of the most controversial aspects of Scleromochlus morphology showing that this taxon retains plesiomorphic features of Avemetatarsalia in the postcranial skeleton, alongside a suite of synapomorphies diagnostic of pterosauromorphs (the broad clade of pterosaurs and taxa more closely related to them than dinosaurs), particularly one subgroup, the lagerpetids. Consistent with recent work, our updated phylogenetic analyses (Maximum Parsimony and Bayesian Inference) demonstrate that Scleromochlus taylori is an avemetatarsalian archosaur that is recovered firmly in an early diverging position within Pterosauromorpha, as a member of Lagerpetidae, thus shedding important information on the origin of pterosaurs, the first group of vertebrates to evolve powered flight.

Hwiccewyrm trispiculum gen. et sp. nov., a new leptopleuronine procolophonid from the Late Triassic of southwest England

The fissure fill localities of southwest England and South Wales are well-known for preserving rich assemblages of predominantly small-bodied Late Triassic to Early Jurassic tetrapods, but many aspects of these assemblages remain contentious. The age of the Late Triassic fissures is disputed, with some lines of argument suggesting a latest Triassic (Rhaetian) age, whereas other evidence suggests they may be as old as Carnian. The fissures have been hypothesized by some workers to have formed on an archipelago, with island effects invoked to explain aspects of the assemblages such as the abundance of small-bodied species. Procolophonids were a successful group of Triassic parareptiles, best known from Early to early Late Triassic assemblages, but have only recently been described from one of the fissure fill sites (Ruthin) based upon fragmentary remains. Here, we describe new procolophonid specimens from another fissure (Cromhall) that represent at least six individuals of different sizes, with much of the skeleton represented including well-preserved skull material. The Cromhall procolophonid shows strong similarities to Late Triassic procolophonids from Scotland, Brazil and North America, but both autapomorphies and a unique character combination demonstrate that it represents a new species, which we name as Hwiccewyrm trispiculum gen. et sp. nov. Phylogenetic analysis places Hwiccewyrm in a derived clade within Leptopleuroninae, together with Leptopleuron, Hypsognathus, and Soturnia. The largest specimens of Hwiccewyrm demonstrate a body size that is similar to Leptopleuron and Hypsognathus, supporting other recent work that has questioned the insular dwarfism hypothesis for the fissure fill assemblages.

Functional morphology of the Triassic apex predator Saurosuchus galilei (Pseudosuchia: Loricata) and convergence with a post-Triassic theropod dinosaur

Pseudosuchian archosaurs, reptiles more closely related to crocodylians than to birds, exhibited high morphological diversity during the Triassic and are thus associated with hypotheses of high ecological diversity during this time. One example involves basal loricatans which are non-crocodylomorph pseudosuchians traditionally known as "rauisuchians." Their large size (5-8+ m long) and morphological similarities to post-Triassic theropod dinosaurs, including dorsoventrally deep skulls and serrated dentitions, suggest basal loricatans were apex predators. However, this hypothesis does not consider functional behaviors that can influence more refined roles of predators in their environment, for example, degree of carcass utilization. Here, we apply finite element analysis to a juvenile but three-dimensionally well-preserved cranium of the basal loricatan Saurosuchus galilei to investigate its functional morphology and to compare with stress distributions from the theropod Allosaurus fragilis to assess degrees of functional convergence between Triassic and post-Triassic carnivores. We find similar stress distributions and magnitudes between the two study taxa under the same functional simulations, indicating that Saurosuchus had a somewhat strong skull and thus exhibited some degree of functional convergence with theropods. However, Saurosuchus also had a weak bite for an animal of its size (1015-1885 N) that is broadly equivalent to the bite force of modern gharials (Gavialis gangeticus). We infer that Saurosuchus potentially avoided tooth-bone interactions and consumed the softer parts of carcasses, unlike theropods and other basal loricatans. This deduced feeding mode for Saurosuchus increases the known functional diversity of basal loricatans and highlights functional differences between Triassic and post-Triassic apex predators.

The skeletal completeness of the Palaeozoic chondrichthyan fossil record

Chondrichthyes (sharks, rays, ratfish and their extinct relatives) originated and diversified in the Palaeozoic but are rarely preserved as articulated or partly articulated remains because of their predominantly cartilaginous endoskeletons. Consequently, their evolutionary history is perceived to be documented predominantly by isolated teeth, scales and fin spines. Here, we aim to capture and analyse the quality of the Palaeozoic chondrichthyan fossil record by using a variation of the skeletal completeness metric, which calculates how complete the skeletons of individuals are compared to estimates of their original entirety. Notably, chondrichthyan completeness is significantly lower than any published vertebrate group: low throughout the Silurian and Permian but peaking in the Devonian and Carboniferous. Scores increase to a range similar to pelycosaurs and parareptiles only when taxa identified solely from isolated teeth, scales and spines are excluded. We argue that environmental influences probably played an important role in chondrichthyan completeness. Sea level significantly negatively correlates with chondrichthyan completeness records and resembles patterns already evident in records of ichthyosaurs, plesiosaurs and sauropodomorphs. Such observed variations in completeness highlight the impact of different sampling biases on the chondrichthyan fossil record and the need to acknowledge these when inferring patterns of chondrichthyan macroevolution.

A new archosauriform species from the Panchet Formation of India and the diversification of Proterosuchidae after the end-Permian mass extinction

Proterosuchidae represents the oldest substantial diversification of Archosauromorpha and plays a key role in understanding the biotic recovery after the end-Permian mass extinction. Proterosuchidae was long treated as a wastebasket taxon, but recent revisions have reduced its taxonomic content to five valid species from the latest Permian of Russia and the earliest Triassic (Induan) of South Africa and China. In addition to these occurrences, several isolated proterosuchid bones have been reported from the Induan Panchet Formation of India for over 150 years. Following the re-study of historical specimens and newly collected material from this unit, we erect the new proterosuchid species Samsarasuchus pamelae, which is represented by most of the presacral vertebral column. We also describe cf. proterosuchid and proterosuchid cranial, girdle and limb bones that are not referred to Samsarasuchus pamelae. Phylogenetic analyses recovered Samsarasuchus pamelae within the new proterosuchid clade Chasmatosuchinae. The taxonomic diversity of Proterosuchidae is substantially expanded here, with at least 11 nominal species and several currently unnamed specimens, and a biogeographical range encompassing present-day South Africa, China, Russia, India, Brazil, Uruguay and Australia. This indicates a broader taxonomic, phylogenetic and biogeographic diversification of Proterosuchidae than previously thought in the aftermath of the end-Permian mass extinction.

New Middle to ?Late Jurassic dinosaur tracksites in the Central High Atlas Mountains, Morocco

Besides bones, fossil tracks and trackways are important sources of knowledge about dinosaur palaeobiology. Here, we report three new tracksites from two different synclines in the Imilchil area, Central High Atlas, Morocco. The tracks and trackways are preserved in fluvial deposits in different levels of the Isli Formation (Early Bathonian-?Upper Jurassic), and contain impressions made by sauropods, theropods and ornithopods, as well as tracks that might represent bird-like non-avian theropod dinosaurs. In addition to traditional field measurements, three-dimensional digital models of the track sites were created using photogrammetry. These new tracksites add to the rich faunal ichnoassemblage already recorded from the High Atlas Mountains and North Africa, which is considerably richer than the contemporaneous body fossil record, and also provide new data on dinosaurs-substrate interactions.

Mechanistic neutral models show that sampling biases drive the apparent explosion of early tetrapod diversity

Estimates of deep-time biodiversity typically rely on statistical methods to mitigate the impacts of sampling biases in the fossil record. However, these methods are limited by the spatial and temporal scale of the underlying data. Here we use a spatially explicit mechanistic model, based on neutral theory, to test hypotheses of early tetrapod diversity change during the late Carboniferous and early Permian, critical intervals for the diversification of vertebrate life on land. Our simulations suggest that apparent increases in early tetrapod diversity were not driven by local endemism following the 'Carboniferous rainforest collapse'. Instead, changes in face-value diversity can be explained by variation in sampling intensity through time. Our results further demonstrate the importance of accounting for sampling biases in analyses of the fossil record and highlight the vast potential of mechanistic models, including neutral models, for testing hypotheses in palaeobiology.

Radial porosity profiles are a powerful tool for tracing locomotor maturation in developing limb bones

Radial porosity profiles (RPP) are a new quantitative osteohistological parameter designed to capture the dynamic changes in the primary porosity of limb bones through ontogeny, providing insights into skeletal growth and functional development of extant and extinct vertebrates. Previous work hypothesized that RPP channelization-the intraskeletal alignment of RPPs across different bones resulting from similar cortical compaction patterns-indicates increasing locomotor performance of the developing limbs. By investigating RPPs in ontogenetic series of pheasants, pigeons and ducks representing distinct locomotor developmental strategies, we test this hypothesis here and show that RPPs are indeed powerful osteohistological correlates of locomotor ontogeny. Qualitative and quantitative analyses reveal strong association between RPP channelization and fledging, the most drastic locomotor transition in the life history of volant birds. The channelization signal is less clear in precocial leg function; however, when additional intraskeletal and intercohort RPP characteristics are considered, patterns related to leg precocity can also be identified. Thus, we demonstrate that RPPs can be used in future by palaeobiologists to generate breakthroughs in the study of the ontogeny and evolution of flight in fossil birds and pterosaurs. With further baseline data collection from modern terrestrial vertebrates, RPPs could also test hypotheses regarding ontogenetic postural shifts in dinosaurs and other terrestrial archosaurs.

Climatic controls on the ecological ascendancy of dinosaurs

The ascendancy of dinosaurs to become dominant components of terrestrial ecosystems was a pivotal event in the history of life, yet the drivers of their early evolution and biodiversity are poorly understood.^1,2,3 During their early diversification in the Late Triassic, dinosaurs were initially rare and geographically restricted, only attaining wider distributions and greater abundance following the end-Triassic mass extinction event.^4,5,6 This pattern is consistent with an opportunistic expansion model, initiated by the extinction of co-occurring groups such as aetosaurs, rauisuchians, and therapsids.^4,7,8 However, this pattern could instead be a response to changes in global climatic distributions through the Triassic to Jurassic transition, especially given the increasing evidence that climate played a key role in constraining Triassic dinosaur distributions.^{7,9,10,11,12,13,14,15,16} Here, we test this hypothesis and elucidate how climate influenced early dinosaur distribution by quantitatively examining changes in dinosaur and tetrapod "climatic niche space" across the Triassic-Jurassic boundary. Statistical analyses show that Late Triassic sauropodomorph dinosaurs occupied a more restricted climatic niche space than other tetrapods and dinosaurs, being excluded from the hottest, low-latitude climate zones. A subsequent, earliest Jurassic expansion of sauropodomorph geographic distribution is linked to the expansion of their preferred climatic conditions. Evolutionary model-fitting analyses provide evidence for an important evolutionary shift from cooler to warmer climatic niches during the origin of Sauropoda. These results are consistent with the hypothesis that global abundance of sauropodomorph dinosaurs was facilitated by climatic change and provide support for the key role of climate in the ascendancy of dinosaurs.

Guttigomphus avilionis gen. et sp. nov., a trirachodontid cynodont from the upper Cynognathus Assemblage Zone, Burgersdorp Formation of South Africa

The Burgersdorp Formation of South Africa is a richly fossiliferous rock sequence at the top of the Permian-Triassic Beaufort Group and is known for its abundance of Early-Middle Triassic vertebrate remains, particularly cynodonts. Fossils from the Burgersdorp Formation are referred biostratigraphically to the Cynognathus Assemblage Zone (CAZ), which is further divided into three subzones: Langbergia-Garjainia, Trirachodon-Kannemeyeria, and Cricodon-Ufudocyclops. Each subzone is characterised by the presence of a distinct species of trirachodontid, a group of gomphodont cynodonts found relatively abundantly throughout the CAZ, with the lower two subzones characterised by the medium-sized trirachodontids Langbergia and Trirachodon. The uppermost part of the formation, the Cricodon-Ufudocyclops subzone, yields trirachodontids of larger size. The majority of these trirachodontid specimens have previously been referred to Cricodon metabolus, a taxon also known from the Manda Beds of Tanzania and the Ntawere Formation of Zambia. Here we identify one of the specimens (BP/1/5538) previously referred to Cricodon as a new taxon, Guttigomphus avilionis. Guttigomphus can be distinguished from other gomphodont cynodonts by features of the upper postcanine teeth, such as an asymmetric crown in occlusal view (crown narrower along the lingual margin than the labial). Our phylogenetic analysis recovers Guttigomphus as a basal member of Trirachodontidae, outside of the clade including Cricodon, Langbergia and Trirachodon.

Radial porosity profiles: a new bone histological method for comparative developmental analysis of diametric limb bone growth

In fossil tetrapods, limb bone histology is considered the most reliable tool not only for inferring skeletal maturity-a crucial assessment in palaeobiological and evolutionary studies-but also for evaluating the growth dynamics within the ontogenetic window represented by the primary bone cortex. Due to its complex relationship with bone growth and functional maturation, primary cortical vascularity is an indispensable osteohistological character for reconstructing growth dynamics, especially in the context of various developmental strategies along the precocial-altricial spectrum. Using this concept as our working hypothesis, we developed a new quantitative osteohistological parameter, radial porosity profile (RPP), that captures relative cortical porosity changes in limb bones as trajectories. We built a proof-of-concept RPP dataset on extant birds, then added fossil paravian dinosaurs and performed a set of trajectory-grouping analyses to identify potential RPP categories and evaluate them in the context of our ontogeny-developmental strategy working hypothesis. We found that RPPs, indeed, reflect important developmental features within and across elements, specimens and taxa, supporting their analytical power. Our RPPs also revealed unexpected potential osteohistological correlates of growth and functional development of limb bones. The diverse potential applications of RPPs open up new research directions in the evolution of locomotor ontogeny.

A new pseudosuchian archosaur, Mambawakale ruhuhu gen. et sp. nov., from the Middle Triassic Manda Beds of Tanzania

The Manda Beds of southwest Tanzania have yielded key insights into the early evolutionary radiation of archosaurian reptiles. Many key archosaur specimens were collected from the Manda Beds in the 1930s and 1960s, but until recently, few of these had been formally published. Here, we describe an archosaur specimen collected in 1963 which has previously been referred to informally as Pallisteria angustimentum. We recognize this specimen as the type of a new taxon, Mambawakale ruhuhu gen. et sp. nov. The holotype and only known specimen of M. ruhuhu comprises a partial skull of large size (greater than 75 cm inferred length), lower jaws and fragments of the postcranium, including three anterior cervical vertebrae and a nearly complete left manus. Mambawakale ruhuhu is characterized by several cranial autapomorphies that allow it to be distinguished with confidence from all other Manda Beds archosaurs, with the possible exception of Stagonosuchus nyassicus for which comparisons are highly constrained due to very limited overlapping material. Phylogenetic analysis suggests that M. ruhuhu is an early diverging pseudosuchian, but more precise resolution is hampered by missing data. Mambawakale ruhuhu is one of the largest known pseudosuchians recovered to date from the Middle Triassic.

Macroevolutionary trends in theropod dinosaur feeding mechanics

Theropod dinosaurs underwent some of the most remarkable dietary changes in vertebrate evolutionary history, shifting from ancestral carnivory^1-3 to hypercarnivory^4,5 and omnivory/herbivory,^6-9 with some taxa eventually reverting to carnivory.^10-12 The mandible is an important tool for food acquisition in vertebrates and reflects adaptations to feeding modes and diets.^13,14 The morphofunctional modifications accompanying the dietary changes in theropod dinosaurs are not well understood because most of the previous studies focused solely on the cranium and/or were phylogenetically limited in scope,^12,15-21 while studies that include multiple clades are usually based on linear measurements and/or discrete osteological characters.^8,22 Given the potential relationship between macroevolutionary change and ontogenetic pattern,²³ we explore whether functional morphological patterns observed in theropod mandibular evolution show similarities to the ontogenetic trajectory. Here, we use finite element analysis to study the mandibles of non-avialan coelurosaurian theropods and demonstrate how feeding mechanics vary between dietary groups and major clades. We reveal an overall reduction in feeding-induced stresses along all theropod lineages through time. This is facilitated by a post-dentary expansion and the development of a downturned dentary in herbivores and an upturned dentary in carnivores likely via the "curved bone effect." We also observed the same reduction in feeding-induced stress in an ontogenetic series of jaws of the tyrannosaurids Tarbosaurus and Tyrannosaurus, which is best attributed to bone functional adaptation. This suggests that this common tendency for structural strengthening of the theropod mandible through time, irrespective of diet, is linked to "functional peramorphosis" of bone functional adaptations acquired during ontogeny.

Cranial functional morphology of the pseudosuchian Effigia and implications for its ecological role in the Triassic

Pseudosuchians, archosaurian reptiles more closely related to crocodylians than to birds, exhibited high morphological diversity during the Triassic with numerous examples of morphological convergence described between Triassic pseudosuchians and post-Triassic dinosaurs. One example is the shuvosaurid Effigia okeeffeae which exhibits an "ostrich-like" bauplan comprising a gracile skeleton with edentulous jaws and large orbits, similar to ornithomimid dinosaurs and extant palaeognaths. This bauplan is regarded as an adaptation for herbivory, but this hypothesis assumes morphological convergence confers functional convergence, and has received little explicit testing. Here, we restore the skull morphology of Effigia, perform myological reconstructions, and apply finite element analysis to quantitatively investigate skull function. We also perform finite element analysis on the crania of the ornithomimid dinosaur Ornithomimus edmontonicus, the extant palaeognath Struthio camelus and the extant pseudosuchian Alligator mississippiensis to assess the degree of functional convergence with a taxon that exhibit "ostrich-like" bauplans and its closest extant relatives. We find that Effigia possesses a mosaic of mechanically strong and weak features, including a weak mandible that likely restricted feeding to the anterior portion of the jaws. We find limited functional convergence with Ornithomimus and Struthio and limited evidence of phylogenetic constraints with extant pseudosuchians. We infer that Effigia was a specialist herbivore that likely fed on softer plant material, a niche unique among the study taxa and potentially among contemporaneous Triassic herbivores. This study increases the known functional diversity of pseudosuchians and highlights that superficial morphological similarity between unrelated taxa does not always imply functional and ecological convergence.

Pendraig milnerae, a new small-sized coelophysoid theropod from the Late Triassic of Wales

We describe a new small-bodied coelophysoid theropod dinosaur, Pendraig milnerae gen. et sp. nov, from the Late Triassic fissure fill deposits of Pant-y-ffynnon in southern Wales. The species is represented by the holotype, consisting of an articulated pelvic girdle, sacrum and posterior dorsal vertebrae, and an associated left femur, and by two referred specimens, comprising an isolated dorsal vertebra and a partial left ischium. Our phylogenetic analysis recovers P. milnerae as a non-coelophysid coelophysoid theropod, representing the first-named unambiguous theropod from the Triassic of the UK. Recently, it has been suggested that Pant-y-ffynnon and other nearby Late Triassic to Early Jurassic fissure fill faunas might have been subjected to insular dwarfism. To test this hypothesis for P. milnerae, we performed an ancestral state reconstruction analysis of body size in early neotheropods. Although our results indicate that a reduced body size is autapomorphic for P. milnerae, some other coelophysoid taxa show a similar size reduction, and there is, therefore, ambiguous evidence to indicate that this species was subjected to dwarfism. Our analyses further indicate that, in contrast with averostran-line neotheropods, which increased in body size during the Triassic, coelophysoids underwent a small body size decrease early in their evolution.

Taxonomic identification bias does not drive patterns of abundance and diversity in theropod dinosaurs

The ability of palaeontologists to correctly diagnose and classify new fossil species from incomplete morphological data is fundamental to our understanding of evolution. Different parts of the vertebrate skeleton have different likelihoods of fossil preservation and varying amounts of taxonomic information, which could bias our interpretations of fossil material. Substantial previous research has focused on the diversity and macroevolution of non-avian theropod dinosaurs. Theropods provide a rich dataset for analysis of the interactions between taxonomic diagnosability and fossil preservation. We use specimen data and formal taxonomic diagnoses to create a new metric, the Likelihood of Diagnosis, which quantifies the diagnostic likelihood of fossil species in relation to bone preservation potential. We use this to assess whether a taxonomic identification bias impacts the non-avian theropod fossil record. We find that the patterns of differential species abundance and clade diversity are not a consequence of their relative diagnosability. Although there are other factors that bias the theropod fossil record that are not investigated here, our results suggest that patterns of relative abundance and diversity for theropods might be more representative of Mesozoic ecology than often considered.

A new Heterodontosaurus specimen elucidates the unique ventilatory macroevolution of ornithischian dinosaurs

Ornithischian dinosaurs were ecologically prominent herbivores of the Mesozoic Era that achieved a global distribution by the onset of the Cretaceous. The ornithischian body plan is aberrant relative to other ornithodiran clades, and crucial details of their early evolution remain obscure. We present a new, fully articulated skeleton of the early branching ornithischian Heterodontosaurus tucki. Phase-contrast enhanced synchrotron data of this new specimen reveal a suite of novel postcranial features unknown in any other ornithischian, with implications for the early evolution of the group. These features include a large, anteriorly projecting sternum; bizarre, paddle-shaped sternal ribs; and a full gastral basket – the first recovered in Ornithischia. These unusual anatomical traits provide key information on the evolution of the ornithischian body plan and suggest functional shifts in the ventilatory apparatus occurred close to the base of the clade. We complement these anatomical data with a quantitative analysis of ornithischian pelvic architecture, which allows us to make a specific, stepwise hypothesis for their ventilatory evolution.

The fossilised skeletons of long extinct dinosaurs are more than just stones. By comparing these remains to their living relatives such as birds and crocodiles, palaeontologists can reveal how dinosaurs grew, moved, ate and socialised. Previous research indicates that dinosaurs were likely warm-blooded and also more active than modern reptiles. This means they would have required breathing mechanisms capable of supplying enough oxygen to allow these elevated activity levels.

So far, much of our insight into dinosaur breathing biology has been biased towards dinosaur species more closely related to modern birds, such as Tyrannosaurus rex, as well as the long-necked sauropods. The group of herbivorous dinosaurs known as ornithischians, which include animals with head ornamentation, spikes and heavy body armour, like that found in Triceratops and Stegosaurus, have often been overlooked. As a result, there are still significant gaps in ornithischian biology, especially in understanding how they breathed.

Radermacher et al. used high-powered X-rays to study a new specimen of the most primitive ornithischian dinosaur, Heterodontosaurus tucki, and discovered that this South African dinosaur has bones researchers did not know existed in this species. These include bones that are part of the breathing system of extant reptiles and birds, including toothpick-shaped bones called gastralia, paired sternal bones and sternal ribs shaped like tennis rackets.

Together, these new pieces of anatomy form a complicated chest skeleton with a large range of motion that would have allowed the body to expand during breathing cycles. But this increased motion of the chest was only possible in more primitive ornithischians. More advanced species lost much of the anatomy that made this motion possible. Radermacher et al. show that while the chest was simpler in advanced species, their pelvis was more specialised and likely played a role in breathing as it does in modern crocodiles.

This new discovery could inform the work of biologists who study the respiratory diversity of both living and extinct species. Differences in breathing strategies might be one of the underlying reasons that some lineages of animals go extinct. It could explain why some species do better than others under stressful conditions, like when the climate is warmer or has less oxygen.

The anatomy and palaeobiology of the early armoured dinosaur Scutellosaurus lawleri (Ornithischia: Thyreophora) from the Kayenta Formation (Lower Jurassic) of Arizona

The armoured dinosaurs, Thyreophora, were a diverse clade of ornithischians known from the Early Jurassic to the end of the Cretaceous. During the Middle and Late Jurassic, the thyreophorans radiated to evolve large body size, quadrupedality, and complex chewing mechanisms, and members of the group include some of the most iconic dinosaurs, including the plated Stegosaurus and the club-tailed Ankylosaurus; however, the early stages of thyreophoran evolution are poorly understood due to a paucity of relatively complete remains from early diverging thyreophoran taxa. Scutellosaurus lawleri is generally reconstructed as the earliest-diverging thyreophoran and is known from over 70 specimens from the Lower Jurassic Kayenta Formation of Arizona, USA. Whereas Scutellosaurus lawleri is pivotal to our understanding of character-state changes at the base of Thyreophora that can shed light on the early evolution of the armoured dinosaurs, the taxon has received limited study. Herein, we provide a detailed account of the osteology of Scutellosaurus lawleri, figuring many elements for the first time. Scutellosaurus lawleri was the only definitive bipedal thyreophoran. Histological studies indicate that it grew slowly throughout its life, possessing lamellar-zonal tissue that was a consequence neither of its small size nor phylogenetic position, but may instead be autapomorphic, and supporting other studies that suggest thyreophorans had lower basal metabolic rates than other ornithischian dinosaurs. Faunal diversity of the Kayenta Formation in comparison with other well-known Early Jurassic-aged dinosaur-bearing formations indicates that there was considerable spatial and/or environmental variation in Early Jurassic dinosaur faunas.

Deep-time biodiversity patterns and the dinosaurian fossil record of the Late Cretaceous Western Interior, North America

In order for palaeontological data to be informative to ecologists seeking to understand the causes of today's diversity patterns, palaeontologists must demonstrate that actual biodiversity patterns are preserved in our reconstructions of past ecosystems. During the Late Cretaceous, North America was divided into two landmasses, Laramidia and Appalachia. Previous work has suggested strong faunal provinciality on Laramidia at this time, but these arguments are almost entirely qualitative. We quantitatively investigated faunal provinciality in ceratopsid and hadrosaurid dinosaurs using a biogeographic network approach and investigated sampling biases by examining correlations between dinosaur occurrences and collections. We carried out a model-fitting approach using generalized least-squares regression to investigate the sources of sampling bias we identified. We find that while the raw data strongly support faunal provinciality, this result is driven by sampling bias. The data quality of ceratopsids and hadrosaurids is currently too poor to enable fair tests of provincialism, even in this intensively sampled region, which probably represents the best-known Late Cretaceous terrestrial ecosystem on Earth. To accurately reconstruct biodiversity patterns in deep time, future work should focus on smaller scale, higher resolution case studies in which the effects of sampling bias can be better controlled.

A Nation-Wide Survey of High School Baseball Coaches' Perceptions Indicates their Arm Care Programs Play a Role in Injury Prevention

BACKGROUND

Arm care programs consisting of upper extremity strengthening and stretching have been recommended for injury prevention for pitchers of all ages. There has been no investigation into high school baseball coaches' usage and perceptions of arm care programs to mitigate physical impairments associated with injuries in baseball players.

HYPOTHESIS/PURPOSE

The purpose of this study was to investigate the current usage of arm care programs by high school baseball coaches. The primary objective was to determine if coaches use group-based or individualized arm care programs. The secondary objective sought to determine if the use of arm care programs is influenced by coaches' age, education, and experience level. Finally, this study explored the potential barriers to arm care implementation and high school baseball coaches' current awareness and beliefs of injury prevention.

STUDY DESIGN

Descriptive cross-sectional survey.

METHODS

A 29-item online survey was emailed to 18,500 high school baseball coaches throughout the United States. Data were collected for three months, and the response rate was 3.7%.

RESULTS

A total of 87.3% (n=571/654) of responding coaches use arm care programs with their players. Of coaches performing arm care, only 18.5% of 571 individualize their arm care exercises based on specific player needs. However, older and more experienced coaches are more likely to individualize their programs. Among the 12.7% (n=83/654) of coaches who do not use arm care programs, the two most commonly cited reasons for not implementing arm care were lack of observed benefit (41%) and insufficient staff (31%). Although 42% of 654 coaches recognized reduced shoulder mobility as a major contributor to injury, risk factors such as throwing with a fatigued arm, previous injury history, and throwing > 8 months per year were not consistently identified as primary risk factors.

CONCLUSION

The results of this study suggest that the majority high school baseball coaches implement group-based arm care exercise programs to prevent injury. Lack of confidence in the effectiveness and staffing limitations were major barriers to implementation of arm care programming. However, the responding coaches exhibited inconsistent risk factor awareness and dated injury prevention beliefs. Therefore, better educational collaboration between rehabilitation professionals and high school coaches regarding injury risk factors and preventative strategies is warranted.

LEVEL OF EVIDENCE

Level 3.

New species of mammaliaform and the cranium of Borealestes (Mammaliformes: Docodonta) from the Middle Jurassic of the British Isles

Docodonta are one of the earliest diverging groups of mammaliaforms, and their morphology provides key information on the transition between non-mammalian cynodonts and Mammalia. We describe the partial skulls of two docodontans Borealestes serendipitus and Borealestes cuillinensis sp. nov. from the Kilmaluag Formation (Middle Jurassic: Bathonian), Isle of Skye, Scotland. We visualize their cranial anatomy using laboratory and synchrotron X-ray micro-CT. The skulls belong to two partial skeletons, currently comprising the most complete Mesozoic mammal fossils reported from the British Isles. The associated upper and lower dentitions show that the lower dentition of Borealestes is not diagnostic to species level. We establish, B. cuillinensis, based on upper molar characters, and re-identify upper molars previously assigned to ‘Borealestes’ mussettae as belonging to B. cuillinensis. ‘Borealestes’ mussettae, based on distinctive lower molars, is found to be morphologically and phylogenetically distinct from Borealestes, necessitating assignment to a new genus, Dobunnodon gen. nov. The skulls of Borealestes retain many plesiomorphic features seen in Morganucodon but absent in more crownward mammaliaforms. Our study highlights that generic and species taxonomy of docodontans are more reliable when based on both upper and lower teeth, while lower molar morphology may underrepresent the true diversity of Mesozoic mammaliaforms.

Impact of nurse burnout on organizational and position turnover

BACKGROUND

The National Academies of Medicine describes clinician burnout as a serious threat to organizational health, including employee turnover.

PURPOSE

To determine the relationship between resilience, burnout, and organizational and position turnover.

METHODS

We surveyed direct care nurses in three hospitals 1 year apart between 2018 and 2019; 1,688 nurses completed 3,135 surveys included in analysis.

FINDINGS

Fifty-four percent of nurses in our sample suffer from moderate burnout, with emotional exhaustion scores increasing by 10% and cynicism scores increasing 19% after 1 year. The impact of burnout on organizational turnover was significant, with a 12% increase in a nurse leaving for each unit increase on the emotional exhaustion scale, though it was not a factor in position turnover.

DISCUSSION

These findings contribute to the growing body of evidence of nurse burnout and support policies and programs for annual measurement of burnout, increased employee wellbeing support, and improved work environments.

The postcranial skeleton of the erythrosuchid archosauriform Garjainia prima from the Early Triassic of European Russia

Erythrosuchidae were large-bodied, quadrupedal, predatory archosauriforms that dominated the hypercarnivorous niche in the aftermath of the Permo-Triassic mass extinction. Garjainia, one of the oldest members of the clade, is known from the late Olenekian of European Russia. The holotype of Garjainia prima comprises a well-preserved skull, but highly incomplete postcranium. Recent taxonomic reappraisal demonstrates that material from a bone bed found close to the type locality, previously referred to as 'Vjushkovia triplicostata', is referable to G. prima. At least, seven individuals comprising cranial remains and virtually the entire postcranium are represented, and we describe this material in detail for the first time. An updated phylogenetic analysis confirms previous results that a monophyletic Garjainia is the sister taxon to a clade containing Erythrosuchus, Shansisuchus and Chalishevia. Muscle scars on many limb elements are clear, allowing reconstruction of the proximal locomotor musculature. We calculate the body mass of G. prima to have been 147-248 kg, similar to that of an adult male lion. Large body size in erythrosuchids may have been attained as part of a trend of increasing body size after the Permo-Triassic mass extinction and allowed erythrosuchids to become the dominant carnivores of the Early and Middle Triassic.

Dietary diversity and evolution of the earliest flying vertebrates revealed by dental microwear texture analysis

Pterosaurs, the first vertebrates to evolve active flight, lived between 210 and 66 million years ago. They were important components of Mesozoic ecosystems, and reconstructing pterosaur diets is vital for understanding their origins, their roles within Mesozoic food webs and the impact of other flying vertebrates (i.e. birds) on their evolution. However, pterosaur dietary hypotheses are poorly constrained as most rely on morphological-functional analogies. Here we constrain the diets of 17 pterosaur genera by applying dental microwear texture analysis to the three-dimensional sub-micrometre scale tooth textures that formed during food consumption. We reveal broad patterns of dietary diversity (e.g. Dimorphodon as a vertebrate consumer; Austriadactylus as a consumer of 'hard' invertebrates) and direct evidence of sympatric niche partitioning (Rhamphorhynchus as a piscivore; Pterodactylus as a generalist invertebrate consumer). We propose that the ancestral pterosaur diet was dominated by invertebrates and later pterosaurs evolved into piscivores and carnivores, shifts that might reflect ecological displacements due to pterosaur-bird competition.

A revision of the early neotheropod genus Sarcosaurus from the Early Jurassic (Hettangian–Sinemurian) of central England

Neotheropoda represents the main evolutionary radiation of predatory dinosaurs and its oldest records come from Upper Triassic rocks (c. 219 Mya). The Early Jurassic record of Neotheropoda is taxonomically richer and geographically more widespread than that of the Late Triassic. The Lower Jurassic (upper Hettangian–lower Sinemurian) rocks of central England have yielded three neotheropod specimens that have been assigned to two species within the genus Sarcosaurus, S. woodi (type species) and S. andrewsi. These species have received little attention in discussions of the early evolution of Neotheropoda and recently have been considered as nomina dubia. Here, we provide a detailed redescription of one of these specimens (WARMS G667–690) and reassess the taxonomy and phylogenetic relationships of the genus Sarcosaurus. We propose that the three neotheropod specimens from the Early Jurassic of central England represent a single valid species, S. woodi. The second species of the genus, ‘S. andrewsi’, is a subjective junior synonym of the former. A quantitative phylogenetic analysis of early theropods recovered S. woodi as one of the closest sister-taxa to Averostra and provides new information on the sequence of character state transformations in the lead up to the phylogenetic split between Ceratosauria and Tetanurae.

The spatial structure of Phanerozoic marine animal diversity

The global fossil record of marine animals has fueled long-standing debates about diversity change through time and the drivers of this change. However, the fossil record is not truly global. It varies considerably in geographic scope and in the sampling of environments among intervals of geological time. We account for this variability using a spatially explicit approach to quantify regional-scale diversity through the Phanerozoic. Among-region variation in diversity is comparable to variation through time, and much of this is explained by environmental factors, particularly the extent of reefs. By contrast, influential hypotheses of diversity change through time, including sustained long-term increases, have little explanatory power. Modeling the spatial structure of the fossil record transforms interpretations of Phanerozoic diversity patterns and their macroevolutionary explanations. This necessitates a refocus of deep-time diversification studies.

The apparent exponential radiation of Phanerozoic land vertebrates is an artefact of spatial sampling biases

There is no consensus about how terrestrial biodiversity was assembled through deep time, and in particular whether it has risen exponentially over the Phanerozoic. Using a database of 60 859 fossil occurrences, we show that the spatial extent of the worldwide terrestrial tetrapod fossil record itself expands exponentially through the Phanerozoic. Changes in spatial sampling explain up to 67% of the change in known fossil species counts, and these changes are decoupled from variation in habitable land area that existed through time. Spatial sampling therefore represents a real and profound sampling bias that cannot be explained as redundancy. To address this bias, we estimate terrestrial tetrapod diversity for palaeogeographical regions of approximately equal size. We find that regional-scale diversity was constrained over timespans of tens to hundreds of millions of years, and similar patterns are recovered for major subgroups, such as dinosaurs, mammals and squamates. Although the Cretaceous/Palaeogene mass extinction catalysed an abrupt two- to three-fold increase in regional diversity 66 million years ago, no further increases occurred, and recent levels of regional diversity do not exceed those of the Palaeogene. These results parallel those recovered in analyses of local community-level richness. Taken together, our findings strongly contradict past studies that suggested unbounded diversity increases at local and regional scales over the last 100 million years.

A unique predator in a unique ecosystem: modelling the apex predator within a Late Cretaceous crocodyliform-dominated fauna from Brazil

Theropod dinosaurs were relatively scarce in the Late Cretaceous ecosystems of southeast Brazil. Instead, hypercarnivorous crocodyliforms known as baurusuchids were abundant and probably occupied the ecological role of apex predators. Baurusuchids exhibited a series of morphological adaptations hypothesized to be associated with this ecological role, but quantitative biomechanical analyses of their morphology have so far been lacking. Here, we employ a biomechanical modelling approach, applying finite element analysis (FEA) to models of the skull and mandibles of a baurusuchid specimen. This allows us to characterize the craniomandibular apparatus of baurusuchids, as well as to compare the functional morphology of the group with that of other archosaurian carnivores, such as theropods and crocodylians. Our results support the ecological role of baurusuchids as specialized apex predators in the continental Late Cretaceous ecosystems of South America. With a relatively weak bite force (~600 N), the predation strategies of baurusuchids likely relied on other morphological specializations, such as ziphodont dentition and strong cervical musculature. Comparative assessments of the stress distribution and magnitude of scaled models of other predators (the theropod Allosaurus fragilis and the living crocodylian Alligator mississippiensis) consistently show different responses to loadings under the same functional scenarios, suggesting distinct predatory behaviors for these animals. The unique selective pressures in the arid to semi-arid Late Cretaceous ecosystems of southeast Brazil, which were dominated by crocodyliforms, possibly drove the emergence and evolution of the biomechanical features seen in baurusuchids, which are distinct from those previously reported for other predatory taxa.

Colobops: a juvenile rhynchocephalian reptile (Lepidosauromorpha), not a diminutive archosauromorph with an unusually strong bite

Correctly identifying taxa at the root of major clades or the oldest clade-representatives is critical for meaningful interpretations of evolution. A small, partially crushed skull from the Late Triassic (Norian) of Connecticut, USA, originally described as an indeterminate rhynchocephalian saurian, was recently named Colobops noviportensis and reinterpreted as sister to all remaining Rhynchosauria, one of the earliest and globally distributed groups of herbivorous reptiles. It was also interpreted as having an exceptionally reinforced snout and powerful bite based on an especially large supratemporal fenestra. Here, after a re-analysis of the original scan data, we show that the skull was strongly dorsoventrally compressed post-mortem, with most bones out of life position. The cranial anatomy is consistent with that of other rhynchocephalian lepidosauromorphs, not rhynchosaurs. The 'reinforced snout' region and the 'exceptionally enlarged temporal region' are preservational artefacts and not exceptional among clevosaurid rhynchocephalians. Colobops is thus not a key taxon for understanding diapsid feeding apparatus evolution.

Cranial anatomy and taxonomy of the erythrosuchid archosauriform 'Vjushkovia triplicostata' Huene, 1960, from the Early Triassic of European Russia

Erythrosuchidae are a globally distributed and important group of apex predators that occupied Early and Middle Triassic terrestrial ecosystems following the Permo-Triassic mass extinction. The stratigraphically oldest known genus of Erythrosuchidae is Garjainia Ochev, 1958, which is known from the late Early Triassic (late Olenekian) of European Russia and South Africa. Two species of Garjainia have been reported from Russia: the type species, Garjainia prima Ochev, 1958, and 'Vjushkovia triplicostata' von Huene, 1960, which has been referred to Garjainia as either congeneric (Garjainia triplicostata) or conspecific (G. prima). The holotype of G. prima has received relatively extensive study, but little work has been conducted on type or referred material attributed to 'V. triplicostata'. However, this material includes well-preserved fossils representing all parts of the skeleton and comprises seven individuals. Here, we provide a comprehensive description and review of the cranial anatomy of material attributed to 'V. triplicostata', and draw comparisons with G. prima. We conclude that the two Russian taxa are indeed conspecific, and that minor differences between them result from a combination of preservation or intraspecific variation. Our reassessment therefore provides additional information on the cranial anatomy of G. prima. Moreover, we quantify relative head size in erythrosuchids and other early archosauromorphs in an explicit phylogenetic context for the first time. Our results show that erythrosuchids do indeed appear to have disproportionately large skulls, but that this is also true for other early archosauriforms (i.e. proterosuchids), and may reflect the invasion of hypercarnivorous niches by these groups following the Permo-Triassic extinction.

Osteology of the archosauromorph Teyujagua paradoxa and the early evolution of the archosauriform skull

Archosauriformes are a major group of fossil and living reptiles that include the crown group Archosauria (birds, crocodilians and their extinct relatives) and closely related taxa. Archosauriformes are characterized by a highly diagnostic skull architecture, which is linked to the predatory habits of their early representatives, and the development of extensive cranial pneumaticity associated with the nasal capsule. The evolution of the archosauriform skull from the more plesiomorphic configuration present ancestrally in the broader clade Archosauromorpha was, until recently, elusive. This began to change with the discovery and description of Teyujagua paradoxa, an early archosauromorph from the Lower Triassic Sanga do Cabral Formation of Brazil. Here, we provide a detailed osteological description of the holotype and, thus far, only known specimen of T. paradoxa. In addition to providing new details of the anatomy of T. paradoxa, our study also reveals an early development of skull pneumaticity prior to the emergence of the antorbital fenestra. We use these new data to discuss the evolution of antorbital openings within Archosauriformes. Reappraisal of the phylogenetic position of T. paradoxa supports previous hypotheses of a close relationship with Archosauriformes. The data presented here provide new insights into character evolution during the origin of the archosauriform skull.

The multi-peak adaptive landscape of crocodylomorph body size evolution

BACKGROUND

Little is known about the long-term patterns of body size evolution in Crocodylomorpha, the > 200-million-year-old group that includes living crocodylians and their extinct relatives. Extant crocodylians are mostly large-bodied (3-7 m) predators. However, extinct crocodylomorphs exhibit a wider range of phenotypes, and many of the earliest taxa were much smaller (< 1.2 m). This suggests a pattern of size increase through time that could be caused by multi-lineage evolutionary trends of size increase or by selective extinction of small-bodied species. Here, we characterise patterns of crocodylomorph body size evolution using a model fitting-approach (with cranial measurements serving as proxies). We also estimate body size disparity through time and quantitatively test hypotheses of biotic and abiotic factors as potential drivers of crocodylomorph body size evolution.

RESULTS

Crocodylomorphs reached an early peak in body size disparity during the Late Jurassic, and underwent an essentially continual decline since then. A multi-peak Ornstein-Uhlenbeck model outperforms all other evolutionary models fitted to our data (including both uniform and non-uniform), indicating that the macroevolutionary dynamics of crocodylomorph body size are better described within the concept of an adaptive landscape, with most body size variation emerging after shifts to new macroevolutionary regimes (analogous to adaptive zones). We did not find support for a consistent evolutionary trend towards larger sizes among lineages (i.e., Cope's rule), or strong correlations of body size with climate. Instead, the intermediate to large body sizes of some crocodylomorphs are better explained by group-specific adaptations. In particular, the evolution of a more aquatic lifestyle (especially marine) correlates with increases in average body size, though not without exceptions.

CONCLUSIONS

Shifts between macroevolutionary regimes provide a better explanation of crocodylomorph body size evolution on large phylogenetic and temporal scales, suggesting a central role for lineage-specific adaptations rather than climatic forcing. Shifts leading to larger body sizes occurred in most aquatic and semi-aquatic groups. This, combined with extinctions of groups occupying smaller body size regimes (particularly during the Late Cretaceous and Cenozoic), gave rise to the upward-shifted body size distribution of extant crocodylomorphs compared to their smaller-bodied terrestrial ancestors.

Description and phylogenetic placement of a new marine species of phytosaur (Archosauriformes: Phytosauria) from the Late Triassic of Austria

Phytosaurs are a group of carnivorous, semi-aquatic archosaurian reptiles that attained an almost global distribution during the Late Triassic. We here describe a new species of the phytosaur genus Mystriosuchus from the Norian Dachstein Limestone of Austria, from a marine lagoonal depositional environment. The new Austrian material comprises remains of at least four individuals of similar size (c. 4 m in total length) found in association but disarticulated, and includes one complete and two partial skulls and postcrania. All of these specimens apparently represent a single taxon, which is distinguished by numerous anatomical features from the two previously named Mystriosuchus species. Maximum parsimony analysis of a comprehensive morphological dataset provides strong statistical support for the phylogenetic position of the new Austrian taxon in Mystriosuchus, as the sister taxon to a clade comprising M. planirostris and M. westphali. Histological analysis suggests that the Austrian phytosaur specimens represent individuals that were at least eight years old at time of death, but which had not yet reached skeletal maturity. Taphonomic and palaeoenvironmental data suggest that these phytosaurs were living in the marine lagoon in which they were preserved, providing the strongest evidence to date of marine adaptations in phytosaurs.

The anatomy and phylogenetic position of the erythrosuchid archosauriform Guchengosuchus shiguaiensis from the earliest Middle Triassic of China

Erythrosuchidae is a clade of early archosauriform reptiles, which were apex predators in many late Early and Middle Triassic ecosystems, following the Permo-Triassic mass extinction. Erythrosuchids had a worldwide distribution, with well-preserved fossil material known from South Africa, European Russia, and China. We here redescribe the anatomy and revise the taxonomy of Guchengosuchus shiguaiensis, which is one of the stratigraphically oldest erythrosuchids and is known from a single partial skeleton from the lowermost Middle Triassic (lower Anisian) lower Ermaying Formation of Shaanxi Province, China. We provide a new differential diagnosis for Guchengosuchus shiguaiensis, and identify a series of autapomorphies relating to the morphologies of the skull roof and vertebrae. Incorporating updated anatomical information for Guchengosuchus into the most comprehensive morphological phylogenetic analysis available for early archosauromorphs recovers it as an early branching member of Erythrosuchidae, outside of the clade formed by Garjainia, Erythrosuchus, Chalishevia, and Shansisuchus. Fugusuchus hejiapanensis, from the uppermost Lower Triassic to lower Middle Triassic Heshanggou Formation of China, is recovered as the earliest branching member of Erythrosuchidae.

Diversity change during the rise of tetrapods and the impact of the 'Carboniferous rainforest collapse'

The Carboniferous and early Permian were critical intervals in the diversification of early four-limbed vertebrates (tetrapods), yet the major patterns of diversity and biogeography during this time remain unresolved. Previous estimates suggest that global tetrapod diversity rose continuously across this interval and that habitat fragmentation following the 'Carboniferous rainforest collapse' (CRC) drove increased endemism among communities. However, previous work failed to adequately account for spatial and temporal biases in sampling. Here, we reassess early tetrapod diversity and biogeography with a new global species-level dataset using sampling standardization and network biogeography methods. Our results support a tight relationship between observed richness and sampling, particularly during the Carboniferous. We found that subsampled species richness initially increased into the late Carboniferous, then decreased substantially across the Carboniferous/Permian boundary before slowly recovering in the early Permian. Our analysis of biogeography does not support the hypothesis that the CRC drove endemism; instead, we found evidence for increased cosmopolitanism in the early Permian. While a changing environment may have played a role in reducing diversity in the earliest Permian, our results suggest that the CRC was followed by increased global connectivity between communities, possibly reflecting both reduced barriers to dispersal and the diversification of amniotes.

A new phylogenetic analysis of Phytosauria (Archosauria: Pseudosuchia) with the application of continuous and geometric morphometric character coding

Phytosauria is a clade of large, carnivorous, semi-aquatic archosauromorphs which reached its peak diversity and an almost global distribution in the Late Triassic (c. 230-201 Mya). Previous phylogenetic analyses of Phytosauria have either focused primarily on the relationships of specific subclades, or were limited in taxonomic scope, and no taxonomically comprehensive dataset is currently available. We here present the most taxonomically comprehensive cladistic dataset of phytosaurs to date, based on extensive first-hand study, identification of novel characters and synthesis of previous matrices. This results in an almost twofold increase in phylogenetic information scored per taxon over previous analyses. Alongside a traditional discrete character matrix, three variant matrices were analysed in which selected characters were coded using continuous and landmarking methods, to more rigorously explore phytosaur relationships. Based on these four data matrices, four tree topologies were recovered. Relationships among non-leptosuchomorph phytosaurs are largely consistent between these four topologies, whereas those of more derived taxa are more variable. Rutiodon carolinensis consistently forms a sister relationship with Angistorhinus. In three topologies Nicrosaurus nests deeply within a group of traditionally non-Mystriosuchini taxa, leading us to redefine Mystriosuchini by excluding Nicrosaurus as an internal specifier. Two distinct patterns of relationships within Mystriosuchini are present in the four topologies, distinguished largely by the variable position of Mystriosuchus. In two topologies Mystriosuchus forms the most basal clade in Mystriosuchini, whilst in the others it occupies a highly derived position within the Machaeroprosopus clade. 'Redondasaurus' is consistently recovered as monophyletic; however, it also nests within the Machaeroprosopus clade. The greatest impact on tree topology was associated with the incorporation of continuous data into our matrices, with landmark characters exerting a relatively modest influence. All topologies correlated significantly with stratigraphic range estimates. Topological variability in our results highlights clades in which further investigation may better elucidate phytosaur relationships.

Pterosaur dietary hypotheses: a review of ideas and approaches

Pterosaurs are an extinct group of Mesozoic flying reptiles, whose fossil record extends from approximately 210 to 66 million years ago. They were integral components of continental and marginal marine ecosystems, yet their diets remain poorly constrained. Numerous dietary hypotheses have been proposed for different pterosaur groups, including insectivory, piscivory, carnivory, durophagy, herbivory/frugivory, filter-feeding and generalism. These hypotheses, and subsequent interpretations of pterosaur diet, are supported by qualitative (content fossils, associations, ichnology, comparative anatomy) and/or quantitative (functional morphology, stable isotope analysis) evidence. Pterosaur dietary interpretations are scattered throughout the literature with little attention paid to the supporting evidence. Reaching a robustly supported consensus on pterosaur diets is important for understanding their dietary evolution, and their roles in Mesozoic ecosystems. A comprehensive examination of the pterosaur literature identified 314 dietary interpretations (dietary statement plus supporting evidence) from 126 published studies. Multiple alternative diets have been hypothesised for most principal taxonomic pterosaur groups. Some groups exhibit a high degree of consensus, supported by multiple lines of evidence, while others exhibit less consensus. Qualitative evidence supports 87.3% of dietary interpretations, with comparative anatomy most common (62.1% of total). More speciose groups of pterosaur tend to have a greater range of hypothesised diets. Consideration of dietary interpretations within alternative phylogenetic contexts reveals high levels of consensus between equivalent monofenestratan groups, and lower levels of consensus between equivalent non-monofenestratan groups. Evaluating the possible non-biological controls on apparent patterns of dietary diversity reveals that numbers of dietary interpretations through time exhibit no correlation with patterns of publication (number of peer-reviewed publications through time). 73.8% of dietary interpretations were published in the 21st century. Overall, consensus interpretations of pterosaur diets are better accounted for by non-biological signals, such as the impact of the respective quality of the fossil record of different pterosaur groups on research levels. That many interpretations are based on qualitative, often untestable lines of evidence adds significant noise to the data. More experiment-led pterosaur dietary research, with greater consideration of pterosaurs as organisms with independent evolutionary histories, will lead to more robust conclusions drawn from repeatable results. This will allow greater understanding of pterosaur dietary diversity, disparity and evolution and facilitate reconstructions of Mesozoic ecosystems.

The rise of the ruling reptiles and ecosystem recovery from the Permo-Triassic mass extinction

One of the key faunal transitions in Earth history occurred after the Permo-Triassic mass extinction (ca 252.2 Ma), when the previously obscure archosauromorphs (which include crocodylians, dinosaurs and birds) become the dominant terrestrial vertebrates. Here, we place all known middle Permian-early Late Triassic archosauromorph species into an explicit phylogenetic context, and quantify biodiversity change through this interval. Our results indicate the following sequence of diversification: a morphologically conservative and globally distributed post-extinction 'disaster fauna'; a major but cryptic and poorly sampled phylogenetic diversification with significantly elevated evolutionary rates; and a marked increase in species counts, abundance, and disparity contemporaneous with global ecosystem stabilization some 5 million years after the extinction. This multiphase event transformed global ecosystems, with far-reaching consequences for Mesozoic and modern faunas.

Nursing Gender Pay Differentials in the New Millennium

BACKGROUND

The gender pay gap in the United States is an ongoing issue, affecting women in nearly all occupations. Jobs traditionally associated with men tend to pay better than traditionally female-dominated jobs, and there is evidence to suggest within-occupation gender pay differences as well.

PURPOSE

We compared and contrasted gender wage disparities for registered nurses (RNs), relative to gender wage disparities for another female-dominated occupation, teachers, while controlling for sociodemographic factors.

METHODS

Using data in the American Community Survey, we analyzed the largest U.S. random representative sample of self-identified RNs and primary or secondary school teachers from 2000 to 2013 using fixed-effects regression analysis.

RESULTS

There is greater disparity between nurse pay by gender than in teacher pay by gender. In addition, the net return in wages for additional education is higher for school teachers (21.7%) than for RNs (4.7%).

CONCLUSIONS

Findings support preferential wages for men in nursing, more so than for men in teaching.

CLINICAL RELEVANCE

The substantial gender disparities are an indirect measure of the misallocation of resources in effective patient care.

Mass extinctions drove increased global faunal cosmopolitanism on the supercontinent Pangaea

Mass extinctions have profoundly impacted the evolution of life through not only reducing taxonomic diversity but also reshaping ecosystems and biogeographic patterns. In particular, they are considered to have driven increased biogeographic cosmopolitanism, but quantitative tests of this hypothesis are rare and have not explicitly incorporated information on evolutionary relationships. Here we quantify faunal cosmopolitanism using a phylogenetic network approach for 891 terrestrial vertebrate species spanning the late Permian through Early Jurassic. This key interval witnessed the Permian–Triassic and Triassic–Jurassic mass extinctions, the onset of fragmentation of the supercontinent Pangaea, and the origins of dinosaurs and many modern vertebrate groups. Our results recover significant increases in global faunal cosmopolitanism following both mass extinctions, driven mainly by new, widespread taxa, leading to homogenous ‘disaster faunas’. Cosmopolitanism subsequently declines in post-recovery communities. These shared patterns in both biotic crises suggest that mass extinctions have predictable influences on animal distribution and may shed light on biodiversity loss in extant ecosystems.

Mass extinctions are thought to produce ‘disaster faunas’, communities dominated by a small number of widespread species. Here, Button et al. develop a phylogenetic network approach to test this hypothesis and find that mass extinctions did increase faunal cosmopolitanism across Pangaea during the late Palaeozoic and early Mesozoic.

Controlling for the species-area effect supports constrained long-term Mesozoic terrestrial vertebrate diversification

Variation in the geographic spread of fossil localities strongly biases inferences about the evolution of biodiversity, due to the ubiquitous scaling of species richness with area. This obscures answers to key questions, such as how tetrapods attained their tremendous extant diversity. Here, we address this problem by applying sampling standardization methods to spatial regions of equal size, within a global Mesozoic-early Palaeogene data set of non-flying terrestrial tetrapods. We recover no significant increase in species richness between the Late Triassic and the Cretaceous/Palaeogene (K/Pg) boundary, strongly supporting bounded diversification in Mesozoic tetrapods. An abrupt tripling of richness in the earliest Palaeogene suggests that this diversity equilibrium was reset following the K/Pg extinction. Spatial heterogeneity in sampling is among the most important biases of fossil data, but has often been overlooked. Our results indicate that controlling for variance in geographic spread in the fossil record significantly impacts inferred patterns of diversity through time.

Species richness increases with area sampled, potentially confounding biodiversity patterns from the fossil record. Here, the authors standardize spatial sampling to control for this bias and show that terrestrial vertebrate diversification was bounded during the Mesozoic but that equilibria were reset following the K/Pg extinction.

The completeness of the fossil record of plesiosaurs, marine reptiles from the Mesozoic

Plesiosaurs were a highly successful group of marine reptiles occurring worldwide in the Jurassic and Cretaceous, but to date few studies have focused on their preservation through time. Here, we conduct the first detailed assessment of the quality of the plesiosaur fossil record. Data was compiled for 178 specimens representing 114 valid species. For each species we calculated the character completeness metric (CCM: percentage of phylogenetic characters from a cladistic dataset that can be scored for that species) and the skeletal completeness metric (SCM: percentage of the overall skeleton that is preserved for that species). Average CCM and SCM values were calculated for individual geological stages. A strong significant positive correlation was recovered between CCM and SCM, suggesting that the two metrics are recording the same signal, at least for this clade. Although a significant correlation between changes in sea level and changes in plesiosaur completeness was not recovered, an underlying negative relationship may be present but obscured by poorly sampled time bins. Plesiosaur completeness though time is not significantly correlated with that for contemporary terrestrial groups (sauropods, pterosaurs, birds), but is significantly correlated with that for ichthyosaurs, suggesting common controls on skeletal preservation in the marine realm. Significantly higher median completeness values in plesiosaurs and ichthyosaurs than in contemporary terrestrial groups support the hypothesis that the marine tetrapod fossil record is more complete than that of terrestrial tetrapods. A collector's curve for plesiosaurs shows a generally slow constant rate of discovery from the latter part of the 19^th century until the 1990s, at which point the rate of discovery increased substantially and shows no sign of slowing. A significant but very weak negative correlation between SCM and the year in which a taxon was named suggests a weak tendency for more recently named species to have less complete skeletons.

A revision of tetrapod footprints from the late Carboniferous of the West Midlands, UK

A series of sandstone slabs from Hamstead, Birmingham (West Midlands, UK), preserve an assemblage of tetrapod trackways and individual tracks from the Enville Member of the Salop Formation (late Carboniferous: late Moscovian-Kasimovian). This material has received limited previous study, despite being one of the few British sites to preserve Carboniferous tetrapod footprints. Here, we restudy and revise the taxonomy of this material, and document it using 3D models produced using photogrammetry. The assemblage is dominated by large tracks assigned to Limnopus isp., which were made by early amphibians (temnospondyls). A number of similar but smaller tracks are assigned to Batrachichnus salamandroides (also made by temnospondyls). Dimetropus leisnerianus (made by early synapsids) and Dromopus lacertoides (made by lizard-like sauropsids such as araeoscelids) are also present. This ichnofauna contrasts with a slightly stratigraphically older, more extensive and better-studied assemblage from Alveley (Shropshire), which is dominated by small amphibians with relatively rare reptiliomorphs, but which lacks Dromopus tracks. The presence of Dromopus lacertoides at Hamstead is consistent with the trend towards increasing aridity through the late Carboniferous. It is possible that the assemblage is the stratigraphically oldest occurrence of this important amniote ichnotaxon.

A revision of Sanpasaurus yaoi Young, 1944 from the Early Jurassic of China, and its relevance to the early evolution of Sauropoda (Dinosauria)

The Early Jurassic of China has long been recognized for its diverse array of sauropodomorph dinosaurs. However, the contribution of this record to our understanding of early sauropod evolution is complicated by a dearth of information on important transitional taxa. We present a revision of the poorly known taxon Sanpasaurus yaoiYoung, 1944 from the late Early Jurassic Ziliujing Formation of Sichuan Province, southwest China. Initially described as the remains of an ornithopod ornithischian, we demonstrate that the material catalogued as IVPP V156 is unambiguously referable to Sauropoda. Although represented by multiple individuals of equivocal association, Sanpasaurus is nonetheless diagnosable with respect to an autapomorphic feature of the holotypic dorsal vertebral series. Additional material thought to be collected from the type locality is tentatively referred to Sanpasaurus. If correctly attributed, a second autapomorphy is present in a referred humerus. The presence of a dorsoventrally compressed pedal ungual in Sanpasaurus is of particular interest, with taxa possessing this typically ‘vulcanodontid’ character exhibiting a much broader geographic distribution than previously thought. Furthermore, the association of this trait with other features of Sanpasaurus that are broadly characteristic of basal eusauropods underscores the mosaic nature of the early sauropod–eusauropod transition. Our revision of Sanpasaurus has palaeobiogeographic implications for Early Jurassic sauropods, with evidence that the group maintained a cosmopolitan Pangaean distribution.

Unappreciated diversification of stem archosaurs during the Middle Triassic predated the dominance of dinosaurs

BACKGROUND

Archosauromorpha originated in the middle-late Permian, radiated during the Triassic, and gave rise to the crown group Archosauria, a highly successful clade of reptiles in terrestrial ecosystems over the last 250 million years. However, scientific attention has mainly focused on the diversification of archosaurs, while their stem lineage (i.e. non-archosaurian archosauromorphs) has often been overlooked in discussions of the evolutionary success of Archosauria. Here, we analyse the cranial disparity of late Permian to Early Jurassic archosauromorphs and make comparisons between non-archosaurian archosauromorphs and archosaurs (including Pseudosuchia and Ornithodira) on the basis of two-dimensional geometric morphometrics.

RESULTS

Our analysis recovers previously unappreciated high morphological disparity for non-archosaurian archosauromorphs, especially during the Middle Triassic, which abruptly declined during the early Late Triassic (Carnian). By contrast, cranial disparity of archosaurs increased from the Middle Triassic into the Late Triassic, declined during the end-Triassic extinction, but re-expanded towards the end of the Early Jurassic.

CONCLUSIONS

Our study indicates that non-archosaurian archosauromorphs were highly diverse components of terrestrial ecosystems prior to the major radiation of archosaurs, including dinosaurs, while disparity patterns of the Ladinian and Carnian indicate a gradual faunal replacement of stem archosaurs by the crown group, including a short interval of partial overlap in morphospace during the Ladinian.

Rating the digital help: electronic medical records, software providers, and physicians

To separate the effects of physicians' characteristics on the perceived productivity of EMRs from the effects of limitations on usability inherent in EMR design, a multivariate regression model is used to estimate the factors influencing physicians' rankings of five attributes of their EMRs, namely; ease of use and reliability; the EMRs effect on physician and staff productivity and the EMRs performance vs. vendor's promises. We divide the factors influencing the rankings into three groups: physician characteristics, EMR characteristics and practice characteristics (type of practice, size, and location). The data are from approximately 1800 practicing physicians in Arizona. Physician's characteristics influence perceived ease of use and physicians' productivity, but not staff productivity, reliability or vendors' promised performance. Practice type and EMR characteristics affect perceived productivity, reliability and performance versus vendors' promises. Vendor-specific effects are highly correlated across all five attributes and are always jointly significant. EMR characteristics are the most significant influence on physicians' perceptions of the EMRs effect on their productivity and that of their staff. Physicians' characteristics (particularly age) have a small but significant influence on perceived productivity.