Sea dragons of Avalon

Tourists driving through the village2 of Street on their way to Glastonbury might well wonder at the representation of a skeleton on the road sign. Could this perhaps be a warning that this stretch of the A39 is a roadkill hotspot? I (Stig Walsh, once a local inhabitant) suspect that the skeleton’s true identity may be far from what most outsiders expect of this part of Somerset (and most locals too). Cider, cheddar cheese, sheepskins, sensible shoes and scratched vinyl LPs of ‘The Best of the Wurzels’ probably rank highly in a top ten list of ‘objects found on and around the Somerset Levels’; Mesozoic ichthyosaurs probably wouldn’t make the top 40. Street nonetheless has an important place in the history of vertebrate palaeontology, and the PalAss review seminar held in late July was organised to look at what can be said about those fossils today

A revision of the ‘coelophysoid-grade’ theropod specimen from the Lower Jurassic of the Isle of Skye (Scotland)

The broadest diversification of early predatory dinosaurs is represented by the ‘coelophysoid-grade’ neotheropods, but their Hettangian–Sinemurian (c. 191–201 Ma) record is scarce worldwide. More information is needed to shed light on the evolution of this dinosaur group after the end-Triassic mass extinction (c. 201 Ma). Here we revisit the anatomy and phylogeny of one of these earliest Jurassic neotheropod specimens, an isolated partial tibia from the lower Sinemurian of the Isle of Skye (Scotland) that was previously identified as probably closely related to Liliensternus liliensterni and coelophysids. However, we found that the Skye specimen is positioned in the branch leading to Averostra (Ceratosauria + Tetanurae), in a polytomy with Sarcosaurus woodi from the late Hettangian–lower Sinemurian of central England and a clade composed of Tachiraptor admirabilis and Averostra. The morphology of the Skye specimen is congruent with that of referred specimens of Sarcosaurus woodi, but because it probably represents a skeletally immature specimen, we assign it to cf. Sarcosaurus woodi. The Skye specimen increases the number of averostran-line neotheropod specimens recorded in the Lower Jurassic of Europe and current evidence indicates that these forms, and not coelophysoids, were relatively common in this part of the world at that time

A reassessment of the postcanine dentition and systematics of the tritylodontid Stereognathus (Cynodontia, Tritylodontidae, Mammaliamorpha), from the Middle Jurassic of the United Kingdom

Tritylodontidae was a successful advanced cynodont clade with a close relationship to mammals, but falling outside the clade Mammaliaformes. Stereognathus ooliticus was the first tritylodontid to be named and described in 1854, but since then no comprehensive description for this species has been produced. A second species, S. hebridicus, was named in 1972 and diagnosed based solely on size difference, being larger than the S. ooliticus holotype. We reexamined all postcanine tooth material attributed to the genus Stereognathus to test the species diagnosis and identify diagnostic morphological characters for this genus. We find no statistical difference in size distribution between S. ooliticus and S. hebridicus postcanine specimens. Specimens previously attributed to the different species fall along an ontogenetic spectrum of size, with no clear clustering. Morphologically, we affirm many previously described features for Stereognathus and identify new morphological features in upper and lower postcanines. We find no morphological features to distinguish these two species, and therefore we synonymize S. hebridicus under S. ooliticus. We reevaluate the scoring of S. ooliticus in previous phylogenetic analyses, generating a new tree using rescored Stereognathus characters. Finally, we suggest that similar reevaluations and redescriptions of other poorly described tritylodontid material are necessary to further clarify relationships among Tritylodontidae and the evolution of characters in derived genera such as Stereognathus.Peer reviewe

Avian cerebellar floccular fossa size is not a proxy for flying ability in birds

Extinct animal behavior has often been inferred from qualitative assessments of relative brain region size in fossil endocranial casts. For instance, flight capability in pterosaurs and early birds has been inferred from the relative size of the cerebellar flocculus, which in life protrudes from the lateral surface of the cerebellum. A primary role of the flocculus is to integrate sensory information about head rotation and translation to stabilize visual gaze via the vestibulo-occular reflex (VOR). Because gaze stabilization is a critical aspect of flight, some authors have suggested that the flocculus is enlarged in flying species. Whether this can be further extended to a floccular expansion in highly maneuverable flying species or floccular reduction in flightless species is unknown. Here, we used micro computed-tomography to reconstruct “virtual” endocranial casts of 60 extant bird species, to extract the same level of anatomical information offered by fossils. Volumes of the floccular fossa and entire brain cavity were measured and these values correlated with four indices of flying behavior. Although a weak positive relationship was found between floccular fossa size and brachial index, no significant relationship was found between floccular fossa size and any other flight mode classification. These findings could be the result of the bony endocranium inaccurately reflecting the size of the neural flocculus, but might also reflect the importance of the flocculus for all modes of locomotion in birds. We therefore conclude that the relative size of the flocculus of endocranial casts is an unreliable predictor of locomotor behavior in extinct birds, and probably also pterosaurs and non-avian dinosaurs

The braincase and inner ear of ‘Metriorhynchus’ cf. ‘M.’ brachyrhynchus – implications for aquatic sensory adaptations in crocodylomorphs

During their long evolutionary history crocodylomorphs achieved a great diversity of body sizes, ecomorphotypes and inferred feeding ecologies. One unique group of crocodylomorphs are the thalattosuchians, which lived during the Jurassic and Cretaceous (ca. 191–125 Ma). They transitioned from shallow marine species, like teleosauroids, into fully pelagic forms with paddle shaped limbs and a vertically orientated tail fluke, the metriorhynchids. The osteological adaptations that allowed metriorhynchids to live in the water are generally well understood, but less is known about their neurosensory and endocranial systems, such as the brain, inner ears, sinuses and cranial nerves and how they relate to their aquatic lifestyle. Based on micro-computed tomography (μCT) data and three-dimensional models, we here describe the braincase and endocranial anatomy of a fully marine metriorhynchid, ‘Metriorhynchus’ cf. ‘M.’ brachyrhynchus (NHMUK PV OR 32617). We found several neuroanatomical features that likely helped this species function in its marine environment. These include a unique flexure in the brain endocast not seen in other thalattosuchians. Other features that have previously been seen in thalattosuchians include enlarged cerebral hemispheres, a hypertrophied venous sinus system, enlarged internal carotid arteries and foramina, and closed/absent lateral pharyngotympanic foramina. The specimen also possesses a pelagic metriorhynchid bony labyrinth morphology, with a compact and dorsoventrally short shape, thick semicircular canals, an enlarged vestibule and potentially a short cochlear duct. A review of character distribution confirms that some of these features evolved at the base of Thalattosuchia in semiaquatic species, long before metriorhynchids became pelagic, suggesting that endocranial anatomy helped allow metriorhynchoids colonize the ocean realm.Fil: Schwab, Julia A.. University of Edinburgh; Reino UnidoFil: Young, Mark T.. University of Edinburgh; Reino UnidoFil: Herrera, Laura Yanina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Witmer, Lawrence. Ohio University; Estados UnidosFil: Walsh, Stig A.. University of Southampton; Reino UnidoFil: Katsamensis, Orestis. Faculty Of Engineering And Physical Sciences; Reino UnidoFil: Brusatte, Stephen L.. University of Edinburgh; Reino Unid

Halcyornis toliapicus (aves: Lower Eocene, England) indicates advanced neuromorphology in Mesozoic Neornithes

Our recent X-ray micro computer-tomographic (μCT) investigations of Prophaethon shrubsolei and Odontopteryx toliapica from the Lower Eocene London Clay Formation of England revealed the avian brain to have been essentially modern in form by 55 Ma, but that an important vision-related synapomorphy of living birds, the eminentia sagittalis of the telencephalon, was poorly developed. This evidence suggested that the feature probably appeared close to the end of the Mesozoic. Here we use μCT analysis to describe the endocranium of Halcyornis toliapicus, also from the London Clay Formation. The affinities of Halcyornis have been hotly debated, with the taxon referred to the Charadriiformes (Laridae), Coraciiformes (Alcedinidae, and its own family Halcyornithidae) and most recently that Halcyornithidae may be a possible senior synonym of Pseudasturidae (Pan-Psittaciformes). Unlike Prophaethon and Odontopteryx, the eminentia sagittalis of Halcyornis is strongly developed and comparable to that of living species. Like those London Clay taxa, the eminentia sagittalis occupies a rostral position on the telencephalon. The senses of Halcyornis appear to have been well developed. The length of the cochlear duct of the inner ear indicates a hearing sensitivity within the upper range of living species, and enlarged olfactory lobes suggest a reasonable reliance on sense of smell. The optic nerves were especially well developed which, together with the strong development of the eminentia sagittalis, indicates a high degree of visual specialization in Halcyornis. The advanced development of the eminentia sagittalis further supports a Mesozoic age for the appearance of this structure and associated neural architectural complexity found in extant Aves. The eminentia sagittalis of living Psittaciformes is situated caudally on the telencephalon, making a Pan-Psittaciformes relationship unlikely for Halcyorni

Revision of Erpetosuchus (Archosauria: Pseudosuchia) and new erpetosuchid material from the Late Triassic ‘Elgin Reptile’ fauna based on µCT scanning techniques

The Late Triassic fauna of the Lossiemouth Sandstone Formation (LSF) from the Elgin area, Scotland, has been pivotal in expanding our understanding of Triassic terrestrial tetrapods. Frustratingly, due to their odd preservation, interpretations of the Elgin Triassic specimens have relied on destructive moulding techniques, which only provide incomplete, and potentially distorted, information. Here, we show that micro-computed tomography (μCT) could revitalise the study of this important assemblage. We describe a long-neglected specimen that was originally identified as a pseudosuchian archosaur, Ornithosuchus woodwardi. μCT scans revealed dozens of bones belonging to at least two taxa: a small-bodied pseudosuchian and a specimen of the procolophonid Leptopleuron lacertinum. The pseudosuchian skeleton possesses a combination of characters that are unique to the clade Erpetosuchidae. As a basis for investigating the phylogenetic relationships of this new specimen, we reviewed the anatomy, taxonomy and systematics of other erpetosuchid specimens from the LSF (all previously referred to Erpetosuchus). Unfortunately, due to the differing representation of the skeleton in the available Erpetosuchus specimens, we cannot determine whether the erpetosuchid specimen we describe here belongs to Erpetosuchus granti (to which we show it is closely related) or if it represents a distinct new taxon. Nevertheless, our results shed light on rarely preserved details of erpetosuchid anatomy. Finally, the unanticipated new information extracted from both previously studied and neglected specimens suggests that fossil remains may be much more widely distributed in the Elgin quarries than previously recognised, and that the richness of the LSF might have been underestimated

Ontogenetic variation in the crocodylian vestibular system

Crocodylians today live in tropical to subtropical environments, occupying mostly shallow waters. Their body size changes drastically during ontogeny, as do their skull dimensions and bite forces, which are associated with changes in prey preferences. Endocranial neurosensory structures have also shown to change ontogenetically, but less is known about the vestibular system of the inner ear. Here we use 30 high-resolution computed tomography (CT) scans and three-dimensional geometric morphometrics to investigate the size and shape changes of crocodylian endosseous labyrinths throughout ontogeny, across four stages (hatchling, juvenile, subadult and adult). We find two major patterns of ontogenetic change. First, the labyrinth increases in size during ontogeny, with negative allometry in relation to skull size. Second, labyrinth shape changes significantly, with hatchlings having shorter semicircular canal radii, with thicker diameters and an overall dorsoventrally shorter labyrinth than those of more mature individuals. We argue that the modification of the labyrinth during crocodylian ontogeny is related to constraints imposed by skull growth, due to fundamental changes in the crocodylian braincase during ontogeny (e.g. verticalisation of the basicranium), rather than changes in locomotion, diet, or other biological functions or behaviours

‘Ear stones’ in crocodylians: a cross-species comparative and ontogenetic survey of otolith structures

The vestibular system of the inner ear is a crucial sensory organ, involved in the sensation of balance and equilibrium. It consists of three semicircular canals that sense angular rotations of the head and the vestibule that detects linear acceleration and gravity. The vestibule often contains structures, known as the otoliths or ‘ear stones’. Otoliths are present in many vertebrates and are particularly well known from the fossil record of fish, but surprisingly have not been described in detail in most tetrapods, living or extinct. Here, we present for the first time a survey of the otoliths of a broad sample of extant crocodylian species, based on computed tomography scans. We find that otoliths are present in numerous crocodylian species of different growth stages, and they continue to increase in size during ontogeny, with positive allometry compared to skull length. Our results confirm that otoliths are a common component of the crocodylian vestibular system, and suggest they play an important role in sensory detection. Otoliths are likely common, but overlooked, constituents of the inner ear in tetrapods, and a broader study of their size, shape and distribution promises insight into sensory abilities