Search

We redescribe the holotype and only known specimen of the early eureptile Coelostegus prothales from the Upper Carboniferous of the Czech Republic using photogrammetric scanning and a virtual 3D rendition of its skull. New information is available on several skull and lower jaw bones, including the postorbital, supratemporal, tabular, postparietal, angular, and prearticular. The new data also permit the correct identification of previously undetected or mis-identified elements (e.g., supratemporal; quadratojugal; angular). We provide an amended diagnosis of Coelostegus and a new reconstruction of the skull in dorsal and lateral views. To evaluate the affinities of Coelostegus, we code this taxon in two recently published taxon-character matrices. Parsimony and Bayesian analyses do not permit firm conclusions on the phylogenetic position of Coelostegus or, indeed, the status and extrinsic relationships of protorothyridid amniotes. Coelostegus emerges either as the sister taxon to the recently redefined Diapsida (Araeoscelidia; Varanopidae; Parareptilia; Neodiapsida), as one of the most basal protorothyridids, or as a derived stem-group amniote in various parsimony-based analyses, or as the basalmost protorothyridid in one Bayesian analysis, with protorothyridids forming a paraphyletic array relative to Diapsida. We review the cranial similarities and differences between Coelostegus and other protorothyridid genera and discuss the implications that various phylogenetic results have for our understanding of early amniote relationships. [ABSTRACT FROM AUTHOR]

Frogs exhibit complex anatomical features of the pelvis, limbs and spine, long assumed to represent specialisations for jumping. Yet frogs employ a wide range of locomotor modes, with several taxa featuring primary locomotor modes other than jumping. Using a combination of techniques (CT imaging and 3D visualization, morphometrics, phylogenetic mapping), this study aims to determine the link between skeletal anatomy and locomotor style, habitat type and phylogenetic history, shedding new light on how functional demands impact morphology. Body and limb measurements for 164 taxa from all the recognised anuran families are extracted from digitally segmented CT scans of whole frog skeletons and analysed using various statistical techniques. We find that the expansion of the sacral diapophyses is the most important variable for predicting locomotor mode, which was more closely correlated with frog morphology than either habitat type or phylogenetic relationships. Predictive analyses suggest that skeletal morphology is a useful indicator of jumping but less so for other locomotor modes, suggesting that there is a wide range of anatomical solutions to performing locomotor styles such as swimming, burrowing or walking. [ABSTRACT FROM AUTHOR]

Temnospondyli are a morphologically varied and ecologically diverse clade of tetrapods that survived for over 200 million years. The body mass of temnospondyls is a key variable in inferring their ecological, physiological and biomechanical attributes. However, estimating the body mass of these extinct creatures has proven difficult because the group has no extant descendants. Here we apply a wide range of body mass estimation techniques developed for tetrapods to the iconic temnospondyls Paracyclotosaurus davidi and Eryops megacephalus. These same methods are also applied to a collection of extant organisms that serve as ecological and morphological analogues. These include the giant salamanders Andrias japonicus and Andrias davidianus, the tiger salamander Ambystoma tigrinum, the California newt Taricha torosa and the saltwater crocodile, Crocodylus porosus. We find that several methods can provide accurate mass estimations across this range of living taxa, suggesting their suitability for estimating the body masses of temnospondyls. Based on this, we estimate the mass of Paracyclotosaurus to have been between 159 and 365 kg, and that of Eryops between 102 and 222 kg. These findings provide a basis for examining body size evolution in this clade across their entire temporal span. [ABSTRACT FROM AUTHOR]

Understanding the evolution of the tetrapod brain is essential to trace the history of ecomorphological diversification of modern clades. While previous studies focused on the morphological transformation of the nervous system along the dinosaur–bird transition, little is known about the brain anatomy of archosauriformes and early archosaurs. Here, we describe the endocast of Euparkeria capensis, a small bodied, terrestrial archosauriform closely related to Archosauria, with the goal of resolving the current uncertainties surrounding the ancestral condition of the archosaurian nervous system. The endocast of Euparkeria is sigmoidal, with large olfactory bulbs, an expanded cerebral hemisphere and an elongated flocculus. We suggest that this pivotal taxon was an active predator with a remarkable olfactory acuity. Overall, the endocast of Euparkeria resembles the ones observed in phytosaurs, crocodilians and early dinosaurs, implying that modern crocodilians retain an archosaurian plesiomorphic brain morphology. [ABSTRACT FROM AUTHOR]

This analysis brings Dresenkamp to a revised definition (p. 96) in which the essence of a musical realization is not identified with the I factual production i of sounds, but rather with their I determination i . In the first, Dresenkamp presents a first (provisional) definition of musical realization (p. 69), and defends it against possible objections. [Extracted from the article]

The earliest known crown‐group lepidosaurs are known from the Middle Triassic; however, their stem group is poorly sampled, with only a few representative fossils found. This is partly due to the small size and delicate bones of early stem‐lepidosaurs (= non‐lepidosaurian lepidosauromorphs), which make both preservation in the fossil record and subsequent discovery less likely. The Middle Jurassic lepidosauromorph Marmoretta oxoniensis is re‐examined using high‐resolution micro‐computed tomography to reveal parts of the skull anatomy that were previously unknown. These include a squamosal, postorbital, more complete parietal, pterygoids, and an articulated posterior section of the mandible. Some differences between this and other Marmoretta specimens were identified as a result, such as the arrangement of palatal teeth and the shape of the parabasisphenoid. The status of Marmoretta as a stem‐lepidosaur or stem‐squamate has been debated. To evaluate this, we tested the phylogenetic position of Marmoretta by including our new data in an adapted phylogenetic character matrix. We recover Marmoretta as a stem‐lepidosaur and sister to Fraxinisaura rozynekae. Our findings support the hypothesis that both taxa belonged to a clade of non‐lepidosaurian lepidosauromorphs that co‐existed with lepidosaurs into the Middle Jurassic. [ABSTRACT FROM AUTHOR]

Cladistic character matrices are routinely repurposed in analyses of morphological disparity. Unfortunately, the sampling of taxa and characters within such datasets reflects their intended application (to resolve phylogeny, rather than distinguish between phenotypes) resulting in tree shapes that often misrepresent broader taxonomic and morphological diversity. Here we use tree shape as a proxy to explore how sampling can affect perceptions of evolving morphological disparity. Through analyses of simulated and empirical data, we demonstrate that sampling can introduce biases in morphospace occupation between clades that are predicted by differences in tree symmetry and branch length distribution. Symmetrical trees with relatively long internal branches predict more expansive patterns of morphospace occupation. Conversely, asymmetrical trees with relatively short internal branches predict more compact distributions. Additionally, we find that long external branches predict greater phenotypic divergence by peripheral morphotypes. Taken together, our results caution against the uncritical repurposing of cladistic datasets in disparity analyses. However, they also demonstrate that when morphological diversity is proportionately sampled, differences in tree shape between clades can speak to genuine differences in morphospace occupation. While cladistic datasets may serve as a useful starting point, disparity datasets must attempt to achieve uniformity in lineage sampling across time and topology. Only when all potential sources of bias are accounted for can evolutionary phenomena be distinguished from artefactual signals. It must be accepted that the non‐uniformity of the fossil record may preclude representative sampling and, therefore, a faithful characterization of the evolution of morphological disparity. [ABSTRACT FROM AUTHOR]

Procolophonoidea was the only parareptile clade to survive the end‐Permian mass extinction, and they experienced a major adaptive radiation during the Triassic. The flourishing of procolophonoid lineages in highly stressful post‐extinction environments may be, at least in part, a result of their early adaptations to herbivory, which would eventually become the most common feeding strategy in later representatives of the group. Although procolophonoids are comparatively diverse in the South African Lystrosaurus declivis Assemblage Zone, only the Gondwanan widespread taxon Procolophon trigoniceps has been thus far reported in South American deposits of similar age. Here, we present a new procolophonid genus and species from the Lower Triassic Sanga do Cabral Formation of Brazil. Oryporan insolitus gen. et sp. nov. combines typical adaptations suggestive of herbivory with primitive character states that are peculiar to early procolophonoids. Accordingly, phylogenetic analysis places the new species as an early‐diverging procolophonid, thus far the phylogenetically earliest to develop apparent adaptations for herbivory. Character optimization shows that the bulbous, labiolingually expanded molariforms of most procolophonids (usually interpreted as indicative of high‐fibre herbivory) were co‐opted from an insectivorous dentition. The new taxon also highlights the diversity of feeding habits displayed by Early Triassic procolophonoids, which was probably crucial for the survival of the clade in post‐extinction disaster communities. [ABSTRACT FROM AUTHOR]

Cladistic datasets of morphological characters are comprised of observations that exhibit varying degrees of consistency with underlying phylogenetic hypotheses, reflecting the acquisition and retention of character states (highly consistent characters), or the convergent evolution and loss of character states (less consistent characters). The consistency between phylogenetic history and individual character histories has a bearing both on the evolutionary process and on the relative ease with which phylogenetic history may be inferred from morphological data. We surveyed 486 tetrapod morphological cladistic datasets to establish an empirical distribution of consistency among characters and datasets. Average dataset size has increased in the number of characters and taxa through time. The Consistency Index measure of homoplasy decreases as more characters are added but the most significant decreases result from the addition of taxa. Retention Index and Homoplasy Excess Ratio remain relatively constant with changes in taxa and character number. Our sampling of larger datasets confirms that the positive relationship between dataset size and homoplasy is primarily caused by an increase in taxa, not an increase in characters. Genealogies of cladistic data matrices for early vertebrates, scalidophorans and crocodilians, which have been modified in succession, show a trend of generally consistent quality through research time. Thus, we find no support for the widely shared conjecture that in the search for phylogenetic resolution, high quality phylogenetic characters are quickly exhausted, with subsequent research leading to the inclusion of potentially misleading characters exhibiting high levels of homoplasy. [ABSTRACT FROM AUTHOR]

Recumbirostran 'microsaurs' are a clade of Palaeozoic tetrapods that possess numerous morphological adaptations for fossorial ecologies. Re‐study of many 'microsaurs' using tomographic methods has provided substantial new data on poorly known anatomy that informs their debated phylogenetic position. Recent studies have identified suites of features among recumbirostrans that place the group within crown Amniota, contrary to hypothesized positions on the amniote stem or the lissamphibian stem. Herein we describe the cranial anatomy of the early Permian gymnarthrid Euryodus dalyae through tomographic analysis of the holotype from South Grandfield, Oklahoma and new specimens from karst deposits near Richards Spur. The braincase of E. dalyae is composed of well‐ossified pleurosphenoids, orbitosphenoids that brace against the skull roof, and unpaired median ossifications. The otic capsules are well‐ossified, and the occiput is unconsolidated. Analysis of the mandibles, typically obscured in articulated specimens, reveals a second tooth row on the dentary, a feature previously unknown in 'microsaurs' that is reminiscent of the condition of the co‐occurring captorhinid Captorhinus aguti. The Richards Spur specimens share many of these features, including the second tooth row, but the neurocranium of the scanned specimen (OMNH 53519) differs from that of the holotype of E. dalyae (e.g. absence of unpaired median ossifications), and these specimens are referred to Euryodus sp. These data add to the growing neurocranial dataset of 'microsaurs', which is essential for iterative reevaluation of early tetrapod phylogeny. This discovery of multiple tooth rows in 'microsaurs' provides further support for the hypothesized close relationships between 'microsaurs' and reptiles. [ABSTRACT FROM AUTHOR]

Cistecephalids are among the most distinctive Permian dicynodonts because of their highly derived skulls and postcrania, which indicate a fossorial ecology. Four cistecephalid species have been described from India, South Africa, and Tanzania; a fifth putative species has been reported from the Luangwa Basin of Zambia but never formally described. Here we present a detailed description of the Luangwa Basin cistecephalid, which we name Kembawacela kitchingi gen. et. sp. nov. The most obvious diagnostic character of K. kitchingi is the presence of caniniform tusks in most specimens. Other important characters include a pineal foramen located at the posterior end of the skull roof; an interparietal that has a pair of anterior processes that extend onto the dorsal surface of the skull, flanking the pineal foramen (but otherwise is restricted to the occipital surface); an undivided nuchal crest; and a trough on the ventral surface of the mid‐ventral vomerine plate. Phylogenetic analysis reconstructs Kembawacela as a basal cistecephalid and confirms that Cistecephalidae is a well‐supported clade. However, relationships within the clade received low branch support. Increased knowledge of cistecephalid diversity shows that they vary in functionally relevant characters, such as degree of inflation of the bony vestibule and the morphology of the scapula and humerus, indicating the need for a more nuanced approach to the relationship between form, function and ecology in the clade. The highly allopatric distribution of cistecephalid species suggests that they experienced strong interspecific competition for limited resources and had limited dispersal ability, similar to extant subterranean mammals. [ABSTRACT FROM AUTHOR]

We here describe the first Neogene record of the squamate clade Mabuyidae. Although this clade has a cosmopolitan distribution today, no pre‐Quaternary fossil record of these reptiles has so far been documented. The material comes from the locality Solnechnodolsk (Russia) and is dated to the late Miocene (MN 13). Although it comprises only jaw elements, it constitutes the first evidence of the occurrence of fossil skinks around the area of the Black Sea. The material is identical to Heremites vittatus, showing the existence of this lineage as early as the late Miocene. Thus, it may be used as a potential calibration point for further studies. The comparative anatomy of the structures of lower jaw in selected scincomorph taxa with a special reference to Mabuya group is presented. The closure of the Meckelian canal is the condition at the basal node of the clade Sphenomorphidae + Eugongylidae + Egerniidae + Mabuyidea, whereas the closed canal in Acontias (Acontidae) evolved independently. However, Sphenomorphidae (Asymblepharus and Scincella) + Eugongylidae (Ablepharus) retain a large anterior opening of the Meckelian canal, whereas only a small opening characterizes the basal node of Egerniidae and Mabuyidae, except for H. vittatus and H. septemtaeniatus. The closure of the Meckelian canal in these two taxa is less well developed in comparison with other mabuyid skinks. Thus, a heterochronic pedomorphic process might have played a role in the evolution of these skinks. The Meckelian canal condition supports the monophyly of Heremites. [ABSTRACT FROM AUTHOR]

Serial sectioning of a nodule encapsulating an adult specimen of the arthrodire placoderm Watsonosteus fletti from the Eday Flagstone Formation (Givetian) in the Orcadian Basin of northern Scotland has revealed the presence of a number of embryos within the adult. This specimen represents the oldest known record of fossilized vertebrate embryos. Thin sections of two of the slices have revealed the detailed histological structure of embryonic plates in placoderms, showing that as previously deduced from visual examination, the outer and inner layers were the first to form. Gut contents preserved near the embryos show that the species had a varied diet, with dermal bone fragments from sarcopterygians and placoderms. [ABSTRACT FROM AUTHOR]

Morphological variation (disparity) is almost invariably characterized by two non‐mutually exclusive approaches: (1) quantitatively, through geometric morphometrics; and (2) in terms of discrete, 'cladistic', or categorical characters. Uncertainty over the comparability of these approaches diminishes the potential to obtain nomothetic insights into the evolution of morphological disparity and the few benchmarking studies conducted so far show contrasting results. Here, we apply both approaches to characterizing morphology in the stem‐gnathostome clade Osteostraci in order to assess congruence between these alternative methods as well as to explore the evolutionary patterns of the group in terms of temporal disparity and the influence of phylogenetic relationships and habitat on morphospace occupation. Our results suggest that both approaches yield similar results in morphospace occupation and clustering, but also some differences indicating that these metrics may capture different aspects of morphology. Phylomorphospaces reveal convergence towards a generalized 'horseshoe'‐shaped cranial morphology and two strong trends involving major groups of osteostracans (benneviaspidids and thyestiids), which probably reflect adaptations to different lifestyles. Temporal patterns of disparity obtained from categorical and morphometric approaches appear congruent, however, disparity maxima occur at different times in the evolutionary history of the group. The results of our analyses indicate that categorical and continuous data sets may characterize different patterns of morphological disparity and that discrepancies could reflect preservational limitations of morphometric data and differences in the potential of each data type for characterizing more or less inclusive aspects of overall phenotype. [ABSTRACT FROM AUTHOR]

The late Viséan anthracosauroid Eldeceeon rolfei from the East Kirkton Limestone of Scotland is re-described. Information from two originally described and two newly identified specimens broadens our knowledge of this tetrapod. A detailed account of individual skull bones and a revision of key axial and appendicular features are provided, alongside the first complete reconstructions of the skull and lower jaw and a revised reconstruction of the postcranial skeleton. In comparison to Silvanerpeton, the only other anthracosauroid from East Kirkton, Eldeceeon is characterised by a proportionally wider semi-elliptical skull, comparatively smaller nostrils set farther apart, smaller and more rounded orbits, a shorter skull table with gently convex lateral margins, and a deeper suspensorium with a straight posterior margin and a small dorsal embayment. The remarkably large hind feet and elongate toes of Eldeceeon presumably represent an adaptation for attaining high locomotory speed through increased stride length and reduced stride frequency. This would necessitate great muscle force but few muscle contractions. At the beginning of a new stride cycle, repositioning the pes anteriorly and lifting the toes off the ground would require a strong and large muscle to pull the femur upward and rotate it inward and forward. It is hypothesised that such muscle might correspond to the puboischiofemoralis internus 2, which would extend along the posterior half of the vertebral column, consistent with the occurrence of long, curved ribs in the anterior half of the trunk. Using maximum parsimony and Bayesian inference, cladistic analyses of all major groups of stem amniotes retrieve a sister group relationship between Eldeceeon and Silvanerpeton, either as the most plesiomorphic stem amniote clade or as a clade immediately crownward of anthracosauroids. [ABSTRACT FROM AUTHOR]

Pleurodires are less diverse than cryptodires, together forming the two major lineages of crown turtles. Their fossil record, however, is rich. A particularly large number of fossil pleurodires, many belonging to the Podocnemidoidae, has been recovered from the Upper Cretaceous Bauru Group outcrops of south‐central Brazil. Herein we describe an additional pleurodire from this region, Amabilis uchoensis gen. et sp. nov., based on a partially preserved skull. A. uchoensis is recognized as belonging to the Podocnemidoidae by the small entrance to the antrum postoticum and completely developed cavum pterygoidei, being unique among other non‐podocnemidid podocnemidoids for its medially open fenestra postotica and absent basioccipital–opisthotic contact. Our cladistic analysis places A. uchoensis as a sister taxon to Hamadachelys + other podocnemidoids. We further explore the neuroanatomy of side‐necked turtles with the aid of micro‐computed tomography of specimens of the main pleurodiran lineages. Our data shed light on the different carotid circulation patterns in pleurodires, and we propose new phylogenetic characters to describe the neuroanatomical variation of the group. Optimization of these characters shows two independent acquisitions of a foramen for the palatal branch of the carotid in chelids and podocnemidoids, and a unique loss of the vidian nerve canal in chelids, in turtles in general. [ABSTRACT FROM AUTHOR]

Placodonts are a group of turtle‐like animals, including placochelyids that are restricted entirely to the Triassic Tethyan realm. Their fossil remains are rare compared with other contemporaneous marine reptiles. Here, we report the first subadult specimen of the placochelyid Psephochelys polyosteoderma from south‐western China. It is the most complete specimen of this taxon known. The new fossil is referred confidently to Psephochelys polyosteoderma on the basis of the narrow and spatulate rostrum, toothless premaxillae, and carapace composed of small and numerous armour plates with relatively smooth surfaces. The new specimen provides additional anatomical information for Psephochelys polyosteoderma including the presence of transverse processes on the dorsal vertebrae lacking anteroposterior expansion, and a phalangeal formula in the pes of 1‐2‐3‐4‐2. The phylogeny of placodonts, especially the family Placochelyidae, is revised based on a character matrix incorporating additional postcranial characters. This resulted in a better‐resolved tree when compared with previous studies, with Psephochelys as a derived genus within Placochelyidae. On comparison with the adult holotype specimen, the incompletely developed armour in the new specimen reveals a fusion pattern of the carapace beginning with the axial and marginal regions. This surface fusion pattern resembles the ontogenetic process in the embryonic turtle shell, hinting at a possible deep homology with their common diapsid ancestor. [ABSTRACT FROM AUTHOR]

The origin of amniotes was a key event in vertebrate evolution, enabling tetrapods to break their ties with water and invade terrestrial environments. Two pivotal clades of early tetrapods, the diadectomorphs and the seymouriamorphs, have played an unsurpassed role in debates about the ancestry of amniotes for over a century, but their skeletal morphology has provided conflicting evidence for their affinities. Using high‐resolution X‐ray microcomputed tomography, we reveal the three‐dimensional architecture of the well preserved endosseous labyrinth of the inner ear in representative species belonging to both groups. Data from the inner ear are coded in a new cladistic matrix of stem and primitive crown amniotes. Both maximum parsimony and Bayesian inference analyses retrieve seymouriamorphs as derived non‐crown amniotes and diadectomorphs as sister group to synapsids. If confirmed, this sister group relationship invites re‐examination of character polarity near the roots of the crown amniote radiation. Major changes in the endosseous labyrinth and adjacent braincase regions are mapped across the transition from non‐amniote to amniote tetrapods and include: a ventral shift of the cochlear recess relative to the vestibule and the semicircular canals; cochlear recess (primitively housed exclusively within the opisthotic) accommodated within both the prootic and the opisthotic; development of a distinct fossa subarcuata. The inner ear of seymouriamorphs foreshadows conditions of more derived groups, whereas that of diadectomorphs shows a mosaic of plesiomorphic and apomorphic traits, some of which are unambiguously amniote‐like, including a distinct and pyramid‐like cochlear recess. [ABSTRACT FROM AUTHOR]