Ossification patterns of the carpus and tarsus in salamanders and impacts of preaxial dominance on the fin-to-limb transition.

Early limb skeletogenesis in salamanders is characterized by preaxial elements, digits I and II forming earlier than their postaxial counterparts (digits III to V), a phenomenon known as preaxial dominance, whereas in amniotes and anurans, these developmental sequences are reversed. This pattern characterizes the late skeletogenesis of digits and zeugopodium of anamniote tetrapods but remains unknown in carpals/tarsals. To correct this gap in knowledge, we investigate the ossification patterns of the carpals/tarsals in six salamander families/clades based on micro-computed tomography scans. We found that preaxial dominance is seen in the distal carpals/tarsals of several salamander clades and diverse early tetrapods, such as temnospondyls and amniotes. This distribution suggests that preaxial dominance is a primitive developmental pattern in tetrapods. Our results demonstrate that the distal carpals/tarsals are developmentally and evolutionarily independent in the autopodium, and preaxial dominance facilitates stabilization of the number of distal carpals/tarsals during fin-to-limb transition and digit reduction in early tetrapods.

Salamander braincase morphology as revealed by micro-computed tomography.

Morphological data sets are misleading in salamander (Caudata) phylogeny due to the relative homoplasy of the dermal skull observed in paedomorphic forms, leading to the trend of excluding morphology when exploring questions of salamander phylogeny. Investigations in caecilians (Gymnophiona) have demonstrated that the inclusion of braincase morphology can rescue morphological phylogenetic analyses and produce topologies congruent with molecular data sets. We scanned 28 species (25 genera) of salamander, representing all 10 families, with high-resolution micro-computed tomography to investigate braincase variation. We describe the morphology of the braincase for all 10 families and distinguish between paedomorphic and metamorphic morphologies. Our results demonstrate a general uniformity amongst metamorphic species with variation largely restricted to the occipito-otic region. A greater range of variation is observed within paedomorphic forms than would be expected when considering the homoplasy of the dermal skull. Obligate paedomorphic forms demonstrate considerably more variation in the anterior braincase than do facultative paedomorphs, which we suggest is evidence of a greater complexity in the evolution and development of these forms than neoteny alone would produce. This raises the question of character independence within morphological data sets and warrants further investigation into the correlation of other characters before morphological data are omitted.

Middle Jurassic stem hynobiids from China shed light on the evolution of basal salamanders.

The Hynobiidae are an early-diverging clade of crown-group salamanders (urodeles) with an important bearing on the evolution of urodeles. Paleobiology and early-branching patterns of the Hynobiidae remain unclear owing to a poorly documented fossil record. We reported a newly referred specimen to the stem hynobiid, originally named as "Liaoxitriton daohugouensis," but here as Neimengtriton daohugouensis comb. nov., and predates the previously estimated origination time of Hynobiidae for at least 8 Myr. We interpret N. daohugouensis as semiaquatic at the adult stage, a previously unknown paleoecological preference among Mesozoic salamanders. Phenotypic variations of N. daohugouensis enlighten an unrecognized association between caudosacral vertebrae and fertilization modes in the early evolution of urodeles. Our cladistic analyses based on morphological characters not only recognize several stem hynobiids and establish Panhynobia nomen cladinovum for the total-group hynobiids but also shed light on the sequential evolution of morphological features in this primitive urodele clade.

Locomotory behaviour of early tetrapods from Blue Beach, Nova Scotia, revealed by novel microanatomical analysis.

Evidence for terrestriality in early tetrapods is fundamentally contradictory. Fossil trackways attributed to early terrestrial tetrapods long predate the first body fossils from the Late Devonian. However, the Devonian body fossils demonstrate an obligatorily aquatic lifestyle. Complicating our understanding of the transition from water to land is a pronounced gap in the fossil record between the aquatic Devonian taxa and presumably terrestrial tetrapods from the later Early Carboniferous. Recent work suggests that an obligatorily aquatic habit persists much higher in the tetrapod tree than previously recognized. Here, we present independent microanatomical data of locomotor capability from the earliest Carboniferous of Blue Beach, Nova Scotia. The site preserves limb bones from taxa representative of Late Devonian to mid-Carboniferous faunas as well as a rich trackway record. Given that bone remodels in response to functional stresses including gravity and ground reaction forces, we analysed both the midshaft compactness profiles and trabecular anisotropy, the latter using a new whole bone approach. Our findings suggest that early tetrapods retained an aquatic lifestyle despite varied limb morphologies, prior to their emergence onto land. These results suggest that trackways attributed to early tetrapods be closely scrutinized for additional information regarding their creation conditions, and demand an expansion of sampling to better identify the first terrestrial tetrapods.

A multimethod approach to the differentiation of enthesis bone microstructure based on soft tissue type.

Whereas there is a wealth of research studying the nature of various soft tissues that attach to bone, comparatively little research focuses on the bone's microscopic properties in the area where these tissues attach. Using scanning electron microscopy to generate a dataset of 1600 images of soft tissue attachment sites, an image classification program with novel convolutional neural network architecture can categorize images of attachment areas by soft tissue type based on observed patterns in microstructure morphology. Using stained histological thin section and liquid crystal cross-polarized microscopy, it is determined that soft tissue type can be quantitatively determined from the microstructure. The primary diagnostic characters are the orientation of collagen fibers and heterogeneity of collagen density throughout the attachment area thickness. These determinations are made across broad taxonomic sampling and multiple skeletal elements.

A platysomid occurrence from the Tournaisian of Nova Scotia.

The Hangenberg extinction has been hypothesized as a first order event in vertebrate evolution; however, information on the earliest Carboniferous vertebrate fauna, crucial in evaluating biodiversity changes, is scarce. Post-extinction recovery has been suggested as the driver of ray-finned fish (actinopterygian) richness increase and differentiation in the Carboniferous. Under this model, actinopterygian postcranial morphology differentiates in the second stage of their radiation. Here, we report on a platysomid occurrence from the Tournaisian of Nova Scotia, Canada. Despite long-standing taxonomic issues with deep-bodied actinopterygians, this specimen represents the earliest known occurrence of one such fish. Its presence in the earliest Carboniferous indicates that actinopterygians were already postcranially differentiated in the aftermath of the Hangenberg. Moreover, this specimen suggests that earliest Carboniferous actinopterygians used multiple locomotory modes; recent data from later Carboniferous taxa suggest that actinopterygian locomotory modes proliferated throughout the Carboniferous. Taken together, these data suggest that early Carboniferous actinopterygians were morphologically, ecologically, and functionally diverse.

A new elasmosaurid (Sauropterygia: Plesiosauria) from the non-marine to paralic Dinosaur Park Formation of southern Alberta, Canada.

Elasmosaurid plesiosaurian remains have been documented from non-marine to paralic (fluvial to estuarine) sediments of the upper Campanian Dinosaur Park Formation (DPF) of southern Alberta since 1898. Despite this long collection history, this material has received relatively little research attention, largely due to the highly fragmentary nature of most recovered specimens. However, this assemblage is significant, as it constitutes a rare occurrence of plesiosaurian remains in a non-marine depositional environment. This study reports on a recently collected and prepared specimen, which represents the most complete elasmosaurid yet collected from the DPF. This specimen preserves the trunk region, the base of the neck and tail, a partial fore and hind limb, and tooth, and is sufficiently complete to be assigned as the holotype of a new genus and species. This new taxon is diagnosed by a distinctive character state combination including a boomerang-shaped clavicular arch with acute anterior process, convex anterolateral margin, deeply embayed posterior margin, and pronounced ventral keel, together with the presence of 22 dorsal vertebrae, and the anterior dorsal centra bearing a ventral notch. The DPF plesiosaurian fossils were recovered from both estuarine/bay and fluvial palaeochannel sediments. The holotype skeleton represents an osteologically mature individual with an estimated body length of around 5 m, although the largest referred DPF elasmosaurid might have been closer to 7 m, which is considerably larger than other plesiosaurians reported from non-marine deposits. This suggests small-body lengths relative to typical elasmosaurids from marine settings, but is consistent with other plesiosaurians recovered from non-marine sediments. The identification of a distinct elasmosaurid taxon in the DPF might be evidence of niche-partitioning among the predominantly oceanic members of the ubiquitous plesiosaurian clade.

Can We Reliably Calibrate Deep Nodes in the Tetrapod Tree? Case Studies in Deep Tetrapod Divergences.

Recent efforts have led to the development of extremely sophisticated methods for incorporating tree-wide data and accommodating uncertainty when estimating the temporal patterns of phylogenetic trees, but assignment of prior constraints on node age remains the most important factor. This depends largely on understanding substantive disagreements between specialists (paleontologists, geologists, and comparative anatomists), which are often opaque to phylogeneticists and molecular biologists who rely on these data as downstream users. This often leads to misunderstandings of how the uncertainty associated with node age minima arises, leading to inappropriate treatments of that uncertainty by phylogeneticists. In order to promote dialogue on this subject, we here review factors (phylogeny, preservational megabiases, spatial and temporal patterns in the tetrapod fossil record) that complicate assignment of prior node age constraints for deep divergences in the tetrapod tree, focusing on the origin of crown-group Amniota, crown-group Amphibia, and crown-group Tetrapoda. We find that node priors for amphibians and tetrapods show high phylogenetic lability and different phylogenetic treatments identifying disparate taxa as the earliest representatives of these crown groups. This corresponds partially to the well-known problem of lissamphibian origins but increasingly reflects deeper instabilities in early tetrapod phylogeny. Conversely, differences in phylogenetic treatment do not affect our ability to recognize the earliest crown-group amniotes but do affect how diverse we understand the earliest amniote faunas to be. Preservational megabiases and spatiotemporal heterogeneity of the early tetrapod fossil record present unrecognized challenges in reliably estimating the ages of tetrapod nodes; the tetrapod record throughout the relevant interval is spatially restricted and disrupted by several major intervals of minimal sampling coincident with the emergence of all three crown groups. Going forward, researchers attempting to calibrate the ages for these nodes, and other similar deep nodes in the metazoan fossil record, should consciously consider major phylogenetic uncertainty, preservational megabias, and spatiotemporal heterogeneity, preferably examining the impact of working hypotheses from multiple research groups. We emphasize a need for major tetrapod collection effort outside of classic European and North American sections, particularly from the southern hemisphere, and suggest that such sampling may dramatically change our timelines of tetrapod evolution.

Ecomorphological associations of scapulocoracoid form in Greater Antillean Anolis lizards.

External morphological metrics have featured prominently in comparative studies examining the morphological convergence that characterizes anoline ecomorphs. To what degree the appendicular-skeletal morphology of Greater Antillean island Anolis lizards tracks their diversity and ecological adaptation, however, remains relatively unexplored. Here we employ computed tomographic scanning techniques to visualize in situ the scapulocoracoid of ecomorph representatives (trunk-ground, trunk-crown, crown-giant, twig) from three islands (Jamaica, Hispaniola, and Puerto Rico), and compare its three-dimensional geometry using qualitative-descriptive and quantitative-morphometric techniques. In contrast to our previous, similarly-conducted study of the pelvic girdle of these same species, the form of the scapulocoracoid varies markedly both within and between species, with much of the variation relating to phylogenetic relationship, specimen size, and assigned ecomorph category. Morphometric variation that correlates with size and/or phylogenetic signal varies between species and cannot be eliminated from the data set without markedly reducing its overall variability. The discovered patterns of skeletal variation are consistent with the demands of locomotor mechanics imposed by the structural configuration of the microhabitat of these ecomorphs. Most pertinently the ecomorphs differ in the anteroposterior length of the coracoid, the dorsoventral height of the scapulocoracoid, the dorsoventral height of the scapula in relation to the height of the suprascapula, and the relative positioning of the borders of the scapulocoracoid fenestra. In the examined ecomorph categories these skeletal differences likely relate to microhabitat usage by permitting different degrees of tilting and displacement of the scapulocoracoid in the parasagittal plane and influencing the sizes of muscle origins and the vectors of their actions. These differences relate to the amount of humeral adduction applied during its protraction, and to the structural stability of the shoulder girdle during acrobatic maneuvers, thus influencing the perch diameter that can be effectively negotiated, a critical factor in the microhabitat structure of Anolis ecomorphs.

New application of strontium isotopes reveals evidence of limited migratory behaviour in Late Cretaceous hadrosaurs.

Dinosaur migration patterns are very difficult to determine, often relying solely on the geographical distribution of fossils. Unfortunately, it is generally not possible to determine if a fossil taxon's geographical distribution is the result of migration or simply a wide distribution. Whereas some attempts have been made to use isotopic systems to determine migratory patterns in dinosaurs, these methods have yet to achieve wider usage in the study of dinosaur ecology. Here, we have used strontium isotope ratios from fossil enamel to reconstruct the movements of an individual hadrosaur from Dinosaur Provincial Park in Alberta, Canada. Results from this study are consistent with a range or migratory pattern between Dinosaur Provincial Park and a contemporaneous locality in the South Saskatchewan River area, Alberta, Canada. This represents a minimum distance of approximately 80 km, which is consistent with migrations seen in modern elephants. These results suggest the continent-wide distribution of some hadrosaur species in the Late Cretaceous of North America is not the result of extremely long-range migratory behaviours.

A method for deducing neck mobility in plesiosaurs, using the exceptionally preserved Nichollssaura borealis.

The elongate-necked aquatic plesiosaurs existed for 135 Myr during the Mesozoic. The function of this elongate neck is a point of debate. Using computed tomography and three-dimensional (3D) modelling, the range of motion (ROM) of the plesiosaur Nichollssaura borealis neck was assessed. To quantify the ROM, the intervertebral mobility was measured along the cervical vertebral column. This was done by manipulating the 3D models in the lateral and dorsoventral directions during two trials. The first assessed the mean intervertebral ROM between pairs of cervical vertebrae along the entire column, and the second assessed ROM with reduced intervertebral spaces. The results suggest that there may be preference for lateral neck movements in N. borealis, which could correspond to an ecological function related to prey capture. This study demonstrates that 3D modelling is an effective tool for assessing function morphology for structures where no good modern analogue exists.

A primitive actinopterygian braincase from the Tournaisian of Nova Scotia.

The vertebrate fossil record of the earliest Carboniferous is notoriously poorly sampled, obscuring a critical interval in vertebrate evolution and diversity. Recent studies of diversity across the Devonian-Carboniferous boundary have proposed a vertebrate mass extinction at the end-Devonian, and recent phylogenies suggest that the origin of the actinopterygian crown may have occurred in the earliest Carboniferous, as part of a broader recovery fauna. However, the data necessary to test this are limited. Here, we describe a partial actinopterygian skull, including diagnostic elements of the posterior braincase, from the Tournaisian Horton Bluff Formation of Blue Beach, Nova Scotia. The braincase surprisingly shows a confluence of characters common in Devonian taxa but absent in Mississippian forms, such as an open spiracular groove; lateral dorsal aortae that pass through open broadly separated, parallel grooves in the ventral otoccipital region, posterior to the articulation of the first infrapharyngobranchial and an intertemporal-supratemporal complex. Phylogenetic analysis places it deep within the actinopterygian stem, among Devonian moythomasiids and mimiids, suggesting more phylogenetically inclusive survivorship of stem group actinopterygians across the end-Devonian mass extinction. With a high lineage survivorship in tetrapods and lungfish across the Devonian-Carboniferous boundary and high vertebrate diversity at Tournaisian localities, this hints at a more gradual turnover between Devonian and Carboniferous vertebrate faunas.

What is bred in the bone: Ecomorphological associations of pelvic girdle form in greater Antillean Anolis lizards.

Ecological niche partitioning of Anolis lizards of the Greater Antillean islands has been the focus of many comparative studies, and much is known about external morphological convergence that characterizes anole ecomorphs. Their internal anatomy, however, has rarely been explored in an ecomorphological context, and it remains unknown to what degree skeletal morphology tracks the diversity and ecological adaptation of these lizards. Herein, we employ CT scanning techniques to visualise the skeleton of the pelvic girdle in situ, and 3D geometric morphometrics to compare the form of the ilium, ischium, and pubis within and between ecomorphs. We examine 26 species of anoles representing four ecomorphs (trunk-ground, trunk-crown, crown-giant, twig) from three islands (Jamaica, Hispaniola, and Puerto Rico). The subtle variations in pelvic girdle morphology discovered are directly associable with all three parameters that we set out to focus on: phylogenetic relationship, specimen size, and assigned ecomorph category. Morphometric variation that correlates with size and/or phylogenetic signal varies between species and cannot be eliminated from the data set without markedly reducing its overall variability. The discovered patterns of skeletal variation are consistent with the demands of locomotor mechanics pertinent to the structural configuration of the microhabitat of three of the four ecomorphs, with the fourth having no discernible distinctive features. This manifests itself chiefly in the relative anteroposterior extent and anteroventral inclination of the ilium and pubis, which differ between ecomorphs and are postulated to reflect optimization of the direction of muscle vectors of the femoral protractors and retractors. Our investigation of the form of the pelvic girdle of anoles allows us to generalize our findings to entire ecomorph categories within a broad phylogenetic and biogeographic context. Differences in the form and configuration of the postcranial skeleton are directly related to ecological patterns.

Hidden morphological diversity among early tetrapods.

Phylogenetic analysis of early tetrapod evolution has resulted in a consensus across diverse data sets in which the tetrapod stem group is a relatively homogenous collection of medium- to large-sized animals showing a progressive loss of 'fish' characters as they become increasingly terrestrial, whereas the crown group demonstrates marked morphological diversity and disparity. The oldest fossil attributed to the tetrapod crown group is the highly specialized aïstopod Lethiscus stocki, which shows a small size, extreme axial elongation, loss of limbs, spool-shaped vertebral centra, and a skull with reduced centres of ossification, in common with an otherwise disparate group of small animals known as lepospondyls. Here we use micro-computed tomography of the only known specimen of Lethiscus to provide new information that strongly challenges this consensus. Digital dissection reveals extremely primitive cranial morphology, including a spiracular notch, a large remnant of the notochord within the braincase, an open ventral cranial fissure, an anteriorly restricted parasphenoid element, and Meckelian ossifications. The braincase is elongate and lies atop a dorsally projecting septum of the parasphenoid bone, similar to stem tetrapods such as embolomeres. This morphology is consistent in a second aïstopod, Coloraderpeton, although the details differ. Phylogenetic analysis, including critical new braincase data, places aïstopods deep on the tetrapod stem, whereas another major lepospondyl lineage is displaced into the amniotes. These results show that stem group tetrapods were much more diverse in their body plans than previously thought. Our study requires a change in commonly used calibration dates for molecular analyses, and emphasizes the importance of character sampling for early tetrapod evolutionary relationships.

Cranial Morphology of the Carboniferous-Permian Tetrapod Brachydectes newberryi (Lepospondyli, Lysorophia): New Data from µCT.

Lysorophians are a group of early tetrapods with extremely elongate trunks, reduced limbs, and highly reduced skulls. Since the first discovery of this group, general similarities in outward appearance between lysorophians and some modern lissamphibian orders (specifically Urodela and Gymnophiona) have been recognized, and sometimes been the basis for hypotheses of lissamphibian origins. We studied the morphology of the skull, with particular emphasis on the neurocranium, of a partial growth series of the lysorophian Brachydectes newberryi using x-ray micro-computed tomography (µCT). Our study reveals similarities between the braincase of Brachydectes and brachystelechid recumbirostrans, corroborating prior work suggesting a close relationship between these taxa. We also describe the morphology of the epipterygoid, stapes, and quadrate in this taxon for the first time. Contra the proposals of some workers, we find no evidence of expected lissamphibian synapomorphies in the skull morphology in Brachydectes newberryi, and instead recognize a number of derived amniote characteristics within the braincase and suspensorium. Morphology previously considered indicative of taxonomic diversity within Lysorophia may reflect ontogenetic rather than taxonomic variation. The highly divergent morphology of lysorophians represents a refinement of morphological and functional trends within recumbirostrans, and is analogous to morphology observed in many modern fossorial reptiles.

Cranial Morphology of the Brachystelechid 'Microsaur' Quasicaecilia texana Carroll Provides New Insights into the Diversity and Evolution of Braincase Morphology in Recumbirostran 'Microsaurs'.

Recumbirostran 'microsaurs,' a group of early tetrapods from the Late Carboniferous and Early Permian, are the earliest known example of adaptation to head-first burrowing in the tetrapod fossil record. However, understanding of the diversity of fossorial adaptation within the Recumbirostra has been hindered by poor anatomical knowledge of the more divergent forms within the group. Here we report the results of µCT study of Quasicaecilia texana, a poorly-known recumbirostran with a unique, broad, shovel-like snout. The organization of the skull roof and braincase of Quasicaecilia is found to be more in line with that of other recumbirostrans than previously described, despite differences in overall shape. The braincase is found to be broadly comparable to Carrolla craddocki, with a large presphenoid that encompasses much of the interorbital septum and the columella ethmoidalis, and a single compound ossification encompassing the sphenoid, otic, and occipital regions. The recumbirostran braincase conserves general structure and topology of braincase regions and cranial nerve foramina, but it is highly variable in the number of ossifications and their extent, likely associated with the reliance on braincase ossifications to resist compression during sediment compaction and mechanical manipulation by epaxial and hypaxial musculature. Expansion of the deep ventral neck musculature in Quasicaecilia, autapomorphic among recumbirostrans, may reflect unique biomechanical function, and underscores the importance of future attention to the role of the cervical musculature in contextualizing the origin and evolution of fossoriality in recumbirostrans.

Micro-CT Study of Rhynchonkos stovalli (Lepospondyli, Recumbirostra), with Description of Two New Genera.

The Early Permian recumbirostran lepospondyl Rhynchonkos stovalli has been identified as a possible close relative of caecilians due to general similarities in skull shape as well as similar robustness of the braincase, a hypothesis that implies the polyphyly of extant lissamphibians. In order to better assess this phylogenetic hypothesis, we studied the morphology of the holotype and three specimens previously attributed to R. stovalli. With the use of micro-computed x-ray tomography (µCT) we are able to completely describe the external and internal cranial morphology of these specimens, dramatically revising our knowledge of R. stovalli and recognizing two new taxa, Aletrimyti gaskillae gen et sp. n. and Dvellacanus carrolli gen et sp. n. The braincases of R. stovalli, A. gaskillae, and D. carrolli are described in detail, demonstrating detailed braincase morphology and new information on the recumbirostran supraoccipital bone. All three taxa show fossorial adaptations in the braincase, sutural articulations of skull roof bones, and in the lower jaw, but variation in cranial morphology between these three taxa may reflect different modes of head-first burrowing behaviors and capabilities. We revisit the homology of the supraoccipital, median anterior bone, and temporal bone of recumbirostrans, and discuss implications of alternate interpretations of the homology of these elements. Finally, we evaluate the characteristics previously used to unite Rhynchonkos stovalli with caecilians in light of these new data. These proposed similarities are more ambiguous than previous descriptions suggest, and result from the composite nature of previous descriptions, ambiguities in external morphology, and functional convergence between recumbirostrans and caecilians for head-first burrowing.

The Braincase and Endosseous Labyrinth of Plioplatecarpus peckensis (Mosasauridae, Plioplatecarpinae), With Functional Implications for Locomotor Behavior.

Adaptations of mosasaurs to the aquatic realm have been extensively studied from the perspective of modifications to the post-cranial skeleton. In recent years, imaging techniques such as computed tomography have permitted the acquisition of anatomical data from previously inaccessible sources. An exquisitely preserved specimen of the plioplatecarpine mosasaur Plioplatecarpus peckensis presents an opportunity to examine the detailed structure of the braincase, as well as the form of the otic capsule endocast. These data elaborate upon previous descriptions of the braincase of Plioplatecarpus, and provide a detailed, three dimensional reconstruction of the osseous labyrinth for the first time. The otic capsule endocasts reveal that the size of the labyrinth relative to head size is comparable to that of other squamates, suggesting that labyrinth size was not a factor in increasing sensitivity. However, all three semicircular canals are tall and strongly arced to a degree comparable to, and even exceeding, that observed in arboreal and aquatic lizards. Comparison of the sensitivity of the canals in each of the three major axes of rotation suggests Plioplatecarpus peckensis may have been most sensitive to movements in the pitch axis. Although early mosasaurs were probably anguilliform swimmers, most are thought to have been subcarangiform to thunniform locomotors with a near-rigid body form and likely decreased maneuverability. The data from the labyrinth presented here add a potential new dimension to this model of locomotion for further consideration, wherein changes in orientation, such as pitch, may have been more common locomotor behaviors than previously thought.

A Diverse Tetrapod Fauna at the Base of 'Romer's Gap'.

The lack of fossil tetrapod bearing deposits in the earliest Carboniferous ('Romer's Gap') has provoked some recent discussions regarding the proximal cause, with three explanations being offered: environmental, taphonomic, and collection failure. One of the few, and earliest, windows into this time is the locality of Blue Beach exposed in the Tournaisian deposits at Horton Bluff lying along the Avon River near Hantsport, Nova Scotia, Canada. This locality has long been known but, because the fossils were deposited in high energy settings they are almost always disarticulated, so the fauna has not been described in detail. Recent intensive collection has revealed a diverse assemblage of material, including for the first time associated elements, which permits an evaluation of the faunal constituents at the locality. Although not diagnosable to a fine taxonomic level, sufficient apomorphies are present to identify representatives from numerous clades known from more complete specimens elsewhere. The evidence suggests a diverse fauna was present, including whatcheeriids and embolomeres. A single humerus previously had been attributed to a colosteid, but there is some uncertainty with this identification. Additional elements suggest the presence of taxa otherwise only known from the late Devonian. Depositional biases at the locality favor tetrapod fossils from larger individuals, but indirect evidence from trackways and tantalizing isolated bones evidences the presence of small taxa that remain to be discovered. The fossils from Blue Beach demonstrate that when windows into the fauna of 'Romer's Gap' are found a rich diversity of tetrapods will be shown to be present, contra arguments that suggested this hiatus in the fossil record was due to extrinsic factors such as atmospheric oxygen levels. They also show that the early tetrapod fauna is not easily divisible into Devonian and Carboniferous faunas, suggesting that some tetrapods passed through the end Devonian extinction event unaffected.

The functional and palaeoecological implications of tooth morphology and wear for the megaherbivorous dinosaurs from the Dinosaur Park Formation (upper Campanian) of Alberta, Canada.

Megaherbivorous dinosaurs were exceptionally diverse on the Late Cretaceous island continent of Laramidia, and a growing body of evidence suggests that this diversity was facilitated by dietary niche partitioning. We test this hypothesis using the fossil megaherbivore assemblage from the Dinosaur Park Formation (upper Campanian) of Alberta as a model. Comparative tooth morphology and wear, including the first use of quantitative dental microwear analysis in the context of Cretaceous palaeosynecology, are used to infer the mechanical properties of the foods these dinosaurs consumed. The phylliform teeth of ankylosaurs were poorly adapted for habitually processing high-fibre plant matter. Nevertheless, ankylosaur diets were likely more varied than traditionally assumed: the relatively large, bladed teeth of nodosaurids would have been better adapted to processing a tougher, more fibrous diet than the smaller, cusp-like teeth of ankylosaurids. Ankylosaur microwear is characterized by a preponderance of pits and scratches, akin to modern mixed feeders, but offers no support for interspecific dietary differences. The shearing tooth batteries of ceratopsids are much better adapted to high-fibre herbivory, attested by their scratch-dominated microwear signature. There is tentative microwear evidence to suggest differences in the feeding habits of centrosaurines and chasmosaurines, but statistical support is not significant. The tooth batteries of hadrosaurids were capable of both shearing and crushing functions, suggestive of a broad dietary range. Their microwear signal overlaps broadly with that of ankylosaurs, and suggests possible dietary differences between hadrosaurines and lambeosaurines. Tooth wear evidence further indicates that all forms considered here exhibited some degree of masticatory propaliny. Our findings reveal that tooth morphology and wear exhibit different, but complimentary, dietary signals that combine to support the hypothesis of dietary niche partitioning. The inferred mechanical and dietary patterns appear constant over the 1.5 Myr timespan of the Dinosaur Park Formation megaherbivore chronofauna, despite continual species turnover.