Dorsal Skull Research Articles

The first record of the genus Prosantorhinus (Perissodactyla: Rhinocerotidae) of East Asia

Abstract Prosantorhinus is a genus of small extinct teleoceratine rhinoceroses with shortened limb bones, widely distributed in Europe. However, the Asian evolution of the teleoceratine Prosantorhinus has remained unclear because of a scarcity of fossil records of the genus. Here, we report the first record of Prosantorhinus in East Asia from the Middle Miocene of Tongxin, Ningxia. The new specimen is characterized by a concave dorsal skull profile and elevated nasals; short and stout nasal bones with drooping margins on both sides; the thickened, enlarged, and roughened nasal extremity supporting a small horn; the semi-molarized upper premolars with a lingual bridge between the protocone and hypocone; the metaloph constriction present on P2–4; the protocone equal to the hypocone on P2; the crista present on P3; and the cement on the cheek teeth developed. With all the morphological evidence considered, we establish a new species, Prosantorhinus yei sp. nov.. A phylogenetic analysis based on 282 morphological characters scored for 36 taxa reveals that Prosantorhinus yei sp. nov. is a relatively derived taxon in the genus. We hypothesize that Prosantorhinus yei sp. nov. lived in relatively moist environments.

Persistent fontanelles in Chihuahuas. Part I. Distribution and clinical relevance.

BackgroundThe Chihuahua dog breed is known for frequent occurrence of a bregmatic fontanelle on the dorsal skull. A common conception is that this skull defect is a clinically irrelevant finding. No studies, however, describe its prevalence or whether it is accompanied by other persistent fontanelles (PFs). Although Chihuahuas are predisposed to Chiari‐like malformation (CM) and syringomyelia (SM), it is unknown whether PFs occur more commonly in dogs with clinical signs that are caused by CM or SM.Hypothesis/ObjectivesTo describe the number and location of PFs at cranial sutures (CSs) and to compare the occurrence of these PFs in dogs with and without CM/SM‐related clinical signs. We hypothesized that PFs also occur commonly at lateral and caudal cranial surfaces, affect a higher number of CSs, and are larger in dogs with CM/SM‐related clinical signs.AnimalsFifty client‐owned Chihuahuas with or without CM/SM‐related clinical signs.ResultsOf the 50 dogs evaluated, 46 (92%) had either 1 or several PFs. The mean ± SD number of PFs was 2.8 ± 3.0 (range, 0‐13). A total of 138 PFs occupied 118 CSs with 57 (48%) located dorsally, 44 (37%) caudally, and 17 (14%) laterally. The number of CSs affected by PFs was significantly higher (P ≤ .001) and total PF area was significantly larger (P = .003) in dogs with CM/SM‐related clinical signs.Conclusions and Clinical ImportancePersistent fontanelles are very common in this group of Chihuahuas and appear at dorsal, lateral, and caudal cranial surfaces. They are more numerous and larger in Chihuahuas with CM/SM‐related clinical signs.

Potentially Neomorphic Cranial Bone Revealed in First Micro‐CT Study of Southern Cassowary Casque Development

Modern cassowaries are a group of flightless birds that possess unusual cranial ornamentation. These bony and keratinous dorsal skull projections, referred to as casques, have been of interest to anatomists for the past two centuries. The osteological configuration of cassowary casques has been described by numerous authors during that period; however, interpretations have differed widely. This ambiguity, arising from purely direct observational studies has prompted the need to redescribe the osteology of cassowary casques across an extensive developmental series (n = 54) using micro-computed tomography (μCT) imaging, digital visualization, and gross dissection. Tracking cranial elements from embryo to adult form in southern cassowaries (Casuarius casuarius) and comparing those bones to non-casqued ratites (Dromaius novaehollandiae and Struthio camelus)revealed that eight distinct cranial bones comprise the casques of adult C. casuarius. The cranial pattern of three paired (nasals, lacrimals, frontals) and two unpaired elements (median casque element, mesethmoid) is unique among the bony ornaments of extant avians. Our analysis documents the median casque element as being distinct from the mesethmoid and absent in other, closely related flightless birds, suggesting this bone is neomorphic in modern cassowaries. This research sets an anatomical baseline for future studies regarding comparative ornament ontogeny and casque function in these poorly-understood birds, as well as the evolutionary and developmental origins of cranial ornamentation across vertebrates.

A new baenid turtle, Palatobaena knellerorum sp. nov., from the lower Paleocene (Danian) Denver Formation of south-central Colorado, U.S.A.

ABSTRACT Baenidae are the most diverse clade of turtles from the latest Cretaceous and earliest Paleogene of North America. Palatobaena species have a distinctive cranial bauplan within baenid turtles and we herein describe a new species, P. knellerorum, based on a complete cranium from the lower Paleocene Denver Formation in the Denver Basin, Colorado. Palatobaena knellerorum differs from other Palatobaena species in the extreme degree of its dorsally oriented orbits, as well as the presence of a broad pentagonal midline crest formed by the supraoccipital and parietals. It can be further diagnosed from other species of Palatobaena by the following unique combination of characters: having a broadly rounded cranium, presence of upper temporal emargination that extends well anterior to the otic chamber, a broad exposure of the supraoccipital on the dorsal skull roof, a broadly rounded ‘tongue groove’ between the maxillae and premaxillae, and a deeply emarginated nasal region that exposes the underlying premaxillae in dorsal view. Palatobaena knellerorum most closely resembles the Maastrichtian/Danian taxon Palatobaena cohen and the Danian taxon P. bairdi. A phylogenetic analysis places P. knellerorum as sister to P. bairdi, and these taxa are sister to P. cohen. Palatobaena knellerorum overlaps in time with P. cohen, but the two are separated geographically with P. knellerorum restricted to the Denver Basin and P. cohen restricted to the Williston Basin. Cranial anatomical data and sedimentological data suggest Palatobaena spp. were bottom dwelling turtles living in shallow water environments that used a putative proboscis to prey upon freshwater-shelled invertebrates.

The Effects of Propofol on Neural Responses in the Mouse Primary Auditory Cortex.

Two-photon laser-scanning microscopy allows for the monitoring of all brain neurons with single-cell and single-action potential accuracy. This study aimed to investigate the neural responses of the primary auditory cortex to sound stimuli in awake and propofol-anesthetized mice using 2-photon laser-scanning microscopy. Twelve healthy adult male C57BL/6 mice were used in the present study. In each mouse, the scalp was removed over the entire dorsal skull, and the right primary auditory cortex (A1) located. The test stimulus, used in the awake and propofol-induced anesthetic state, was a group of tones with a random combination of 3 sound intensities and 8 sound frequencies. The calcium indicator GCaMP6s was virally expressed in cortical neurons and neuronal activity was recorded using 2-photon imaging. Calcium responses to sound stimuli in two thirds of the neuronal population of the A1 layer were significantly inhibited by propofol anesthesia. In a single neuron, the calcium responses were also inhibited by propofol anesthesia. In the waking state, △F/F (where F is the time series of fluorescence intensity) of all single neurons was significantly higher than that in the propofol-induced anesthetic state (n=669, P<0.001). Finally, in one example session and averaged across different fields of views (n=6 sessions), the response events to sound stimuli were also inhibited by propofol anesthesia. Anesthetic doses of propofol inhibited calcium transients and neuronal activity in the primary auditory cortex of mice.

An Osteo‐Developmental Baseline for Cranial Casque Anatomy of Southern Cassowaries Better Informs Functional Interpretations

Seemingly bizarre cranial ornaments can be found among most major tetrapod groups. The casques (i.e., dorsal skull projections of bone surrounded by keratin sheathing) of modern cassowaries (Casuarius) are perhaps the most enigmatic of modern Aves. Both the biological role(s) and anatomical configuration of this headgear has been debated for the past 150 years, limiting our understanding of the life history of these unique birds as well as the selective conditions under which cranial elaborations appear in archosaurs. Because these structures are poorly understood, it is essential to set an osteo‐developmental foundation from which biomechanical, behavioral, physiological, and functional studies can radiate from. To address the commonly proposed roles of cassowary casques (e.g., ramming, vocalization, thermoregulation, display), we conducted μCT analyses of cranial anatomy in a developmental series of southern cassowaries (C. casuarius). This allowed us to describe details of both external and internal anatomy as well as timings of sutural fusions and inflations of casque elements. We compared the developmental timing of casques to physical, behavioral, and reproductive maturity to determine the plausibility of each function. Our sample (n = 130) indicates the majority of casque growth occurs prior to sexual maturity; although, casque morphology changes substantially throughout adulthood. Deviation from midline is particularly common in the casques of C. casuarius and such asymmetries appear to be primarily dextral. Form does not support functions for either physical ramming or vocalization; however, thermoregulation and display are not refuted by ontogeny nor adult phenotype, necessitating more focused future study.Support or Funding Information2019 New York Institute of Technology College of Osteopathic Medicine (Akinobu Watanabe)2019 Western Interior Paleontological Society ‐ Karl Hirsch Memorial Grant (Todd L. Green)2018 American Association of Anatomists ‐ Visiting Scholarship (Todd L. Green)2017 National Science Foundation ‐ Major Research Instrumentation Grant (Paul M. Gignac)2016 Western Interior Paleontological Society ‐ Karl Hirsch Memorial Grant (Todd L. Green)2015 National Science Foundation ‐ Early‐concept Grant for Exploratory Research (Paul M. Gignac)2015 National Science Foundation ‐ Division of Environmental Biology (Paul M. Gignac)

The impact of the different habitats on skull variation in the fossorial subterranean rodents (Rodentia: Spalacidae) from Middle Anatolia

AbstractIn this study, the morphometric variations were investigated in Farmland and Hillside populations of subterranean rodent Nannospalax xanthodon from Central Anatolia. A total of 31 parameters were measured in the skull and mandible of 35 male individuals. Multivariate analysis (MVA) of the obtained cranial data was used to determine the parameters that varied between habitats and chromosomal populations (2n = 54 and 2n = 60). Furthermore, the effect of soil hardness on the morphology of the dorsal skull of male and female individuals was investigated. As a result, habitat differences caused some morphometric variations in the skull dorsal, especially facial bones, whereas the samples with diploid chromosome number 2n = 54 and 2n = 60 were separated by eight cranial parametric measurements. Accordingly, the known effect of ecological factors on phylogenetic variations in digging animals has first discussed in Nannospalax xantodon cytotypes.

Revision of the European species of Prosantorhinus (Mammalia, Perissodactyla, Rhinocerotidae)

t is not size that distinguishes the genus Prosantorhinus from Diaceratherium , but the following characters: a concave dorsal skull profile with upslanting nasals and narrowing on the distal side of the last upper molar. Using these characters, in addition to the type species Prosantorhinus germanicus (), the following species can be added to the genus: Prosantorhinus douvillei () (, .), from the Early and Middle Miocene (MN 3–5) of Western Europe, Prosantorhinus laubei from MN 3 of northern Bohemia, Prosantorhinus aurelianensis () from MN 3–4a of Western Europe, and with some reservation “Rhinoceros” tagicus (), an enigmatic species from the Early Miocene (MN 3) of Portugal, known only by its upper cheek teeth. At the beginning of MN 3 (), the metapodials of Prosantorhinus aurelianensis were considerably more robust than those of the latest Diaceratherium species (Laugnac, MN 2b) (.) Within the genus shortening of the distal limb segments and narrowing of the distal side of M3 increased with time. The metapodials of Prosantorhinus laubei are less robust but of medium length, in contrast to the Middle Miocene (MN 5) Prosantorhinus germanicus in which they are extremely shortened. No transitional species or co-occurrence of Diaceratherium and Prosantorhinus are known.

An enigmatic marine reptile, Hispaniasaurus cranioelongatus (gen. et sp. nov.) with nothosauroid affinities from the Ladinian of the Iberian Range (Spain)

An incomplete skull of a marine reptile with an atypical elongation of the postorbital region is described. The find comes from the Muschelkalk facies (Cañete Formation) of the Villora section (Iberian Range, Cuenca Province, Spain), characterised by a shallow marine (intertidal) environment and dated as Ladinian in age. The small skull has a rectangular shape, lacking, as preserved, upper temporal openings and a parietal foramen. The upper temporal openings might be secondarily closed. However, the absence of a parietal foramen and squamosals in the preserved part and the incompleteness of the pterygoids make a posteriorly postponed location of the upper temporal openings also conceivable. Teeth are all broken off but alveolar spaces indicate large and massive maxillary dentition. Micro-CT-data revealed a highly vascularised inner structure of the dorsal skull elements, which might indicate special feeding adaptations. Adding the new find to an existing phylogenetic analysis of Triassic marine reptiles reveals eosauropterygian, especially nothosauroid, affinities. However, morphological differences to nothosauroids justify the erection of a new genus and species for this enigmatic marine reptile. Its atypical morphology, without any extinct or modern analogue, fits well with the continuously increasing diversity of Triassic marine reptiles, exhibiting various specialised feeding strategies urn:lsid:zoobank.org:act:6D75AEC7-A5C5-4844-B71A-8215AB099134

Dimorphism in the Skull Form of Golden Jackals (Canis aureus Linnaeus, 1758) in the Western Balkans: A Geometric Morphometric Approach

Geometric morphometrics analyses are now often used to examine morphological variation in carnivore skull. Differences in golden jackal skull shape and size due to sexual dimorphism were examined using two dimensional geometric morphometrics approach. A total of 21 landmarks described the dorsal side of the skull and lateral side of the mandible. Individual variation in skull and mandible morphology was statistically significant for the shape (p<0.01). Sexual dimorphism as main effect was highly significant for the dorsal skull shape and the mandible shape and size (p<0.01). The comparison of mandible mean shapes using discriminant function analysis and parametric test did not reveal significant differences between the sexes, while dorsal mean skull shape was statistically significant (p<0.05). The shape comparison between males and females using permutation tests with procrustes distance yielded with significant results for both skull and mandible shape. Further studies are required with increased sample size and number of landmarks so as to obtain a more accurate expression of form and better differentiation between the sexes.

An early geikiid dicynodont from the Tropidostoma Assemblage Zone (late Permian) of South Africa.

Based on specimens previously identified as Tropidostoma, a new taxon of dicynodont (Bulbasaurus phylloxyron gen. et sp. nov.) from the Karoo Basin of South Africa is described. Bulbasaurus is a medium-sized dicynodont (maximum dorsal skull length 16.0 cm) restricted to the Tropidostoma Assemblage Zone (early Lopingian) of the Beaufort Group. Bulbasaurus can be distinguished from Tropidostoma by an array of characters including the presence of a tall, sharp premaxillary ridge, large, rugose, nearly-confluent nasal bosses, a nasofrontal ridge, massive tusks, robust pterygoids, prominently twisted subtemporal bar, and absence of a distinct postfrontal. Inclusion of Bulbasaurus in a phylogenetic analysis of anomodont therapsids recovers it as a member of Geikiidae, a clade of otherwise later Permian dicynodonts such as Aulacephalodon and Pelanomodon. Bulbasaurus exhibits many of the characters typical of adult Aulacephalodon, but at substantially smaller skull size (these characters are absent in comparably-sized Aulacephalodon juveniles), suggesting that the evolution of typical geikiid morphology preceded gigantism in the clade. Bulbasaurus is the earliest known geikiid and the only member of the group known from the Tropidostoma Assemblage Zone; discovery of this taxon shortens a perplexing ghost lineage and indicates that abundant clades from the later Permian of South Africa (e.g., Geikiidae, Dicynodontoidea) may have originated as rare components of earlier Karoo assemblage zones.

Evolutionary morphology of the rabbit skull.

The skull of leporids (rabbits and hares) is highly transformed, typified by pronounced arching of the dorsal skull and ventral flexion of the facial region (i.e., facial tilt). Previous studies show that locomotor behavior influences aspects of cranial shape in leporids, and here we use an extensive 3D geometric morphometrics dataset to further explore what influences leporid cranial diversity. Facial tilt angle, a trait that strongly correlates with locomotor mode, significantly predicts the cranial shape variation captured by the primary axis of cranial shape space, and describes a small proportion (13.2%) of overall cranial shape variation in the clade. However, locomotor mode does not correlate with overall cranial shape variation in the clade, because there are two district morphologies of generalist species, and saltators and cursorial species have similar morphologies. Cranial shape changes due to phyletic size change (evolutionary allometry) also describes a small proportion (12.5%) of cranial shape variation in the clade, but this is largely driven by the smallest living leporid, the pygmy rabbit (Brachylagus idahoensis). By integrating phylogenetic history with our geometric morphometric data, we show that the leporid cranium exhibits weak phylogenetic signal and substantial homoplasy. Though these results make it difficult to reconstruct what the ‘ancestral’ leporid skull looked like, the fossil records suggest that dorsal arching and facial tilt could have occurred before the origin of the crown group. Lastly, our study highlights the diversity of cranial variation in crown leporids, and highlights a need for additional phylogenetic work that includes stem (fossil) leporids and includes morphological data that captures the transformed morphology of rabbits and hares.

A New Brachylophosaurin Hadrosaur (Dinosauria: Ornithischia) with an Intermediate Nasal Crest from the Campanian Judith River Formation of Northcentral Montana.

BackgroundBrachylophosaurini is a clade of hadrosaurine dinosaurs currently known from the Campanian (Late Cretaceous) of North America. Its members include: Acristavus gagslarsoni, which lacks a nasal crest; Brachylophosaurus canadensis, which possesses a flat paddle-shaped nasal crest projecting posteriorly over the dorsal skull roof; and Maiasaura peeblesorum, which possesses a dorsally-projecting nasofrontal crest. Acristavus, from the lower Two Medicine Formation of Montana (~81–80 Ma), is hypothesized to be the ancestral member of the clade. Brachylophosaurus specimens are from the middle Oldman Formation of Alberta and equivalent beds in the Judith River Formation of Montana; the upper Oldman Formation is dated 77.8 Ma.Methodology/Principal FindingsA new brachylophosaurin hadrosaur, Probrachylophosaurus bergei (gen. et sp. nov.) is described and phylogenetically analyzed based on the skull and postcranium of a large individual from the Judith River Formation of northcentral Montana (79.8–79.5 Ma); the horizon is equivalent to the lower Oldman Formation of Alberta. Cranial morphology of Probrachylophosaurus, most notably the nasal crest, is intermediate between Acristavus and Brachylophosaurus. In Brachylophosaurus, the nasal crest lengthens and flattens ontogenetically, covering the supratemporal fenestrae in large adults. The smaller nasal crest of Probrachylophosaurus is strongly triangular in cross section and only minimally overhangs the supratemporal fenestrae, similar to an ontogenetically earlier stage of Brachylophosaurus. Sutural fusion and tibial osteohistology reveal that the holotype of Probrachylophosaurus was relatively more mature than a similarly large Brachylophosaurus specimen; thus, Probrachylophosaurus is not simply an immature Brachylophosaurus.Conclusions/SignificanceThe small triangular posteriorly oriented nasal crest of Probrachylophosaurus is proposed to represent a transitional nasal morphology between that of a non-crested ancestor such as Acristavus and the large flat posteriorly oriented nasal crest of adult Brachylophosaurus. Because Probrachylophosaurus is stratigraphically and morphologically intermediate between these taxa, Probrachylophosaurus is hypothesized to be an intermediate member of the Acristavus-Brachylophosaurus evolutionary lineage.

The ontogenetic origins of skull shape disparity in the Triturus cristatus group.

Comparative studies of ontogenies of closely related species provide insights into the mechanisms responsible for morphological diversification. Using geometric morphometrics, we investigated the ontogenetic dynamics of postlarval skull shape and disparity in three closely related crested newt species. The skull shapes of juveniles just after metamorphosis (hereafter metamorphs) and adult individuals were sampled by landmark configurations that describe the shape of the dorsal and ventral side of the newt skull, and analyzed separately. The three species differ in skull size and shape in metamorphs and adults. The ontogenies of dorsal and ventral skull differ in the orientation but not lengths of the ontogenetic trajectories. The disparity of dorsal skull shape increases over ontogeny, but that of ventral skull shape does not. Thus, modifications of ontogenetic trajectories can, but need not, increase the disparity of shape. In species with biphasic life-cycles, when ontogenetic trajectories for one stage can be decoupled from those of another, increases and decreases in disparity are feasible, but our results show that they need not occur.

The Roots of Amphibian Morphospace: A Geometric Morphometric Analysis of Paleozoic Temnospondyls

Abstract Temnospondyls—a major component of Permian and Carboniferous terrestrial ecosystems—display great diversity in skull shapes and proportions. To quantify and interpret this diversity, we conducted a geometric morphometric analysis using 45 landmarks on the dorsal skull surface of 90 species with well-represented cranial material. Results show a correlation between morphospace occupation and phylogenetic proximity of taxa for trees in which dvinosaurs and dissorophoids are sister groups and join an edopoid-–eryopoid–basal archegosauriform clade. Most large groups of Carboniferous and Permian temnospondyls occupy specific areas of morphospace. Nearest-neighbor analyses reveal significantly greater taxon clustering than expected under either uniform or Gaussian null models. Size correlates strongly with shape across the whole data set, highlighting the association of some features (short, broad snout; large orbits) with small size. A significant relationship between size and shape is not observed in ...

Cerebrovascular responses of the rat brain to noxious stimuli as examined by functional near-infrared whole brain imaging

While near-infrared (NIR) spectroscopy has been increasingly used to detect stimulated brain activities with an advantage of dissociating regional oxy- and deoxyhemoglobin concentrations simultaneously, it has not been utilized much in pain research. Here, we investigated and demonstrated the feasibility of using this technique to obtain whole brain hemodynamics in rats and speculated on the functional relevance of the NIR-based hemodynamic signals during pain processing. NIR signals were emitted and collected using a 26-optodes array on rat's dorsal skull surface after the removal of skin. Following the subcutaneous injection of formalin (50 μl, 3%) into a hindpaw, several isolable brain regions showed hemodynamic changes, including the anterior cingulate cortex, primary/secondary somatosensory cortexes, thalamus, and periaqueductal gray (n = 6). Time courses of hemodynamic changes in respective regions matched with the well-documented biphasic excitatory response. Surprisingly, an atypical pattern (i.e., a decrease in oxyhemoglobin concentration with a concomitant increase in deoxyhemoglobin concentration) was seen in phase II. In a separate group of rats with innocuous brush and noxious pinch of the same area (n = 11), results confirmed that the atypical pattern occurred more likely in the presence of nociception than nonpainful stimulation, suggesting it as a physiological substrate when the brain processes pain. In conclusion, the NIR whole brain imaging provides a useful alternative to study pain in vivo using small-animal models. Our results support the notion that neurovascular response patterns depend on stimuli, bringing attention to the interpretation of vascular-based neuroimaging data in studies of pain.

Spatial Memory Deficits and Their Correlations with Clusters of Shrunken Neuronal Soma in the Cortices and Limbic System Following a “Mild’’ Mechanical Impact to the Dorsal Skull in Female Rats

Background: Previous results showed that quantitative changes in behavioural accuracies by rats that sustained a “mild” closed head injury were moderately correlated with the total areas (numbers) of anomalous neuronal soma within regions below the impact. Method: Water maze behavioural measures within one day or two months after a single impact of mechanical force over the right dorsal skull, with or without stunning and with or without subsequent pregnancy, were measured and compared to proportions of anomalous neurons under the impact site. Results: The consequences of the impact accommodated about 20% of the variance in the rats’ scores for less proficient spatial learning and memory. There were significantly more anomalous cells within right hemisphere below the impact site that were correlated with poorer initial maze learning. Maternal experience reduced the numbers of anomalous cells in the right limbic area only. Conclusion: These results suggest weak mechanical impacts produce changes in histomorphology within some neurons that are still evident two months later and that the presence of these anomalous clusters, corresponding to less than 1% of the cross-sectional area and below the resolution of contemporary MRI in human cases, are strongly correlated with specific behavioural impairments.

A phylogenetic view on skull size and shape variation in the smooth newt ( Lissotriton vulgaris , Caudata, Salamandridae)

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No relationship between canalization and developmental stability of the skull in a natural population ofMastomys natalensis(Rodentia: Muridae)

The aim of the present work was to investigate the relationship between canalization and developmental stability under varying environmental conditions. Three different cohorts of Mastomys natalensis (Rodentia, Muridae), displaying different growth trajectories, were analysed by means of geometric morphometrics. A set of 23 landmarks was digitalized on the dorsal skull of 292 specimens from Morogoro (Tanzania). Patterns of among- and within-individual (measured as fluctuating asymmetry, FA) variation were assessed and compared among and within the three groups to test for the presence of a common mechanism between canalization and developmental stability. Results showed that there was no congruence between canalization and developmental stability: (1) levels of FA and among-individual variation varied in a discordant fashion, (2) no correspondence between the variance–covariance matrix of among- and within individual variation was found, and (3) environmental effects were able to alter the covariance structure of among-individual variation leaving patterns associated with fluctuating asymmetry unaffected. These findings support the view of multiple mechanisms underlying developmental buffering of shape variation. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104, 207–216.

The cranial morphology of a new genus of lungfish (Osteichthyes: Dipnoi) from the Upper Jurassic Morrison Formation of North America

ABSTRACT Much of Mesozoic diversity within the lungfishes (Osteichthyes: Dipnoi) has traditionally been relegated to the genus Ceratodus, primarily on the basis of the highly stereotypical dental plates characteristic of post-Devonian lungfishes. The new genus Potamoceratodus contains the single species P. guentheri (Marsh, 1878), comb. nov. Newly discovered material allows clarification of the features of this species, including description of a complete skull roof and partial palate. The new genus can be differentiated from the European Ceratodus on the basis of characters of the skull roof, palate, and dentition, including lack of tubercular ornamentation of the skull roof, modest convexity of the dorsal skull roof, absence of sensory sulci anteriorly in the EF bone, and an enlarged and elongate anterior odontode series on the pterygoid dental plate. The North American Ceratodus record is reexamined in light of more complete material from the Temple Canyon localities of the Morrison Formation of Colorado, USA. Ceratodus is found to be an assemblage of forms with disparate cranial morphology. The succession of North American lungfish communities in the late Paleozoic and Mesozoic is most characteristic of serial replacement rather than in situ evolution, and it is possible that the isolation of North America subsequent to the breakup of Laurentia contributed to the regional extinction of lungfishes in North America.