Three-dimensional Skull Research Articles

Correlation between head shape and volumetric changes following spring-assisted posterior vault expansion

The aim of the study was to investigate whether different head shapes show different volumetric changes following spring-assisted posterior vault expansion (SA-PVE) and to investigate the influence of surgical and morphological parameters on SA-PVE.Preoperative three-dimensional skull models from patients who underwent SA-PVE were extracted from computed tomography scans. Patient head shape was described using statistical shape modelling (SSM) and principal component analysis (PCA). Preoperative and postoperative intracranial volume (ICV) and cranial index (CI) were calculated. Surgical and morphological parameters included skull bone thickness, number of springs, duration of spring insertion and type of osteotomy.In the analysis, 31 patients were included. SA-PVE resulted in a significant ICV increase (284.1 ± 171.6 cm3, p < 0.001) and a significant CI decrease (−2.9 ± 4.3%, p < 0.001). The first principal component was significantly correlated with change in ICV (Spearman ρ = 0.68, p < 0.001). Change in ICV was significantly correlated with skull bone thickness (ρ = −0.60, p < 0.001) and age at time of surgery (ρ = −0.60, p < 0.001). No correlations were found between the change in ICV and number of springs, duration of spring insertion and type of osteotomy.SA-PVE is effective for increasing the ICV and resolving raised intracranial pressure. Younger, brachycephalic patients benefit more from surgery in terms of ICV increase. Skull bone thickness seems to be a crucial factor and should be assessed to achieve optimal ICV increase. In contrast, insertion of more than two springs, duration of spring insertion or performing a fully cut through osteotomy do not seem to impact the ICV increase. When interpreting ICV increases, normal calvarial growth should be taken into account.

Osteology and digital reconstruction of the skull of the early tetrapod Whatcheeria deltae

ABSTRACT The Early Carboniferous stem tetrapod Whatcheeria deltae is among the earliest-branching limbed tetrapods represented by multiple near-complete specimens, making it an important taxon in understanding the vertebrate water-to-land transition. However, all preserved skulls of Whatcheeria suffer from post-mortem crushing and lateral compression, which has made cranial reconstruction problematic. In this study, computed tomography data of three Whatcheeria specimens were segmented using visualization software to digitally separate each individual skull bone from matrix. Digital methods were used to repair and retrodeform the bones and produce the first complete three-dimensional skull reconstruction of Whatcheeria. We provide a revised description of the cranial and lower jaw anatomy of Whatcheeria based on CT data, focusing on sutural morphology and previously unknown anatomical details. Our findings suggest that Whatcheeria had one of the narrowest skulls of any known early tetrapod, a gap between the nasals, and significant overlap of the lacrimal onto the nasal and prefrontal. Sutural morphology is used to infer loading regime in the skull during feeding and suggests the skull of Whatcheeria was well adapted to resist stresses induced by biting large prey with its enlarged anterior fangs.

Craniofacial Reconstruction Based on Geodesic Regression Model

<p indent=0mm>Craniofacial reconstruction refers to predicting the corresponding appearance based on the characteristics of an unknown skull. In order to solve the problem of large amount of data, manual work of calibrating feature points and difficulty in defining craniofacial feature points in the process of craniofacial reconstruction, for the three-dimensional skull and skin model represented by a triangular mesh, the craniofacial model is represented by a set of geodesics which are starting from the tip of a nose, thereby craniofacial reconstruction method based on geodesic regression is proposed. First, a set of geodesics is extracted from the nose tip point of the 3D face model; then the skull and the geodesics extracted from the corresponding face model are used as training samples, and the partial least square regression statistical model is used to reconstruct geodesics corresponding to the unknown skull; Finally, the iterative closest point algorithm is used to match the geodesics generated by the geodesic regression method with the facial statistical model to reconstruct the face of the test skull. Craniofacial reconstruction experiments have been conducted on 192 sets of craniofacial data. The reconstruction results based on geodesic regression were compared with the reconstruction results of principal component analysis and partial least squares regression. The experimental results showed that our method can improve the reconstruction accuracy, reduce the reconstruction time, and achieve a good reconstruction effect.

Three-Dimensional Skull Model for Endoscopic Skull Base Surgical Training

Nebor, Ivanna; Hussein, Ahmed; Montemagno, Kora; Fumagalli, Rebecca; Labiad, Ikrame; Anderson, Zoe; Xu, Alice; Sedaghat, Ahmad; Patil, Yash; Forbes, Jonathan A MD Author Information

Robotic stereotaxic system based on 3D skull reconstruction to improve surgical accuracy and speed

BackgroundSome experimental approaches in neuroscience research require the precise placement of a recording electrode, pipette or other tool into a specific brain area that can be quite small and/or located deep beneath the surface. This process is typically aided with stereotaxic methods but remains challenging due to a lack of advanced technology to aid the experimenter. Currently, procedures require a significant amount of skill, have a high failure rate, and take up a significant amount of time. New methodWe developed a next generation robotic stereotaxic platform for small rodents by combining a three-dimensional (3D) skull profiler sub-system and a full six degree-of-freedom (6DOF) robotic platform. The 3D skull profiler is based on structured illumination in which a series of horizontal and vertical line patterns are projected onto an animal skull. These patterns are captured by two two-dimensional (2D) CCD cameras which reconstruct an accurate 3D skull surface profile based on structured illumination and geometrical triangulation. Using the reconstructed 3D profile, the skull can be repositioned using a 6DOF robotic platform to accurately align a surgical tool. ResultsThe system was evaluated using mechanical measurement techniques, and the accuracy of the platform was demonstrated using agar brain phantoms and animal skulls. Additionally, a small and deep brain nucleus (the medial nucleus of the trapezoid body) were targeted in rodents to confirm the targeting accuracy. ConclusionsThe new stereotaxic system can accomplish “skull-flat” rapidly and precisely and with minimal user intervention, and thus reduces the failure rate of such experiments.

Bioanthropological analysis of human occipital condyles using geometric morphometric method.

Sex differences are present in all parts of the body, including the skeletal system. Several methods are used to analyze the sex differences of skeleton, while more recently, a new method called geometric morphometry has been used. The aim of this study was to examine the sexual dimorphism of occipital condyles on human skulls originating from the population of Bosnia and Herzegovina using the geometric morphometric method.Material and methodsThe study was conducted on 214 human skulls of known gender from Bosnian population. For analysis of sexual dimorphism of occipital condyles, we used geometric morphometry, where all the skulls were scanned to obtain three-dimensional skull models. On the obtained models, we marked anthropometric points on occipital condyles in a Landmark Editor program from which we exported data in the form NTSYS file and analyzed it in MorphoJ program.ResultsFirst principal component PC1 describes 26.917% of total variability, the second principal component PC2 describes 20.992% of total variability, while the first eight principal components together describe 100% of total variability. The greatest variability between the male skulls and female skulls was present in the anterior-posterior diameter (length of occipital condyles). Discriminant functional analysis of the shape and size of the occipital condyles was possible with 69.50% accuracy for male skulls and with 60.27% accuracy for female skulls. The size of the occipital condyles showed a statistically significant effect on sexual determination. Discriminant functional analysis of the shape of the occipital condyles without affecting size enabled the determination of gender with with 65.96% accuracy for male skulls and with 63.01% accuracy for female skulls.ConclusionAnalysis of sexual dimorphism of occipital condyles using geometric morphometry showed statistically significant differences in the shape and size of occipital condyles between the sexes. The accuracy of sex determination based on occipital condyles was higher for male gender.

Development of a sex estimation method for skulls using machine learning on three-dimensional shapes of skulls and skull parts

• A sex estimation method for skulls using machine learning was developed. • Homologous three-dimensional skull shapes with 40,962 vertices were modeled. • Partial least squares regression (PLS) was applied to dimensionality reduction. • Support vector machine (SVM) effectively classified the sex using PLS components. • Greater reliability is expected by increasing the training data for the SVM. Sex estimation from the skull plays an important role in the identification of skeletal remains. A novel sex estimation method from three-dimensional shapes of the skull using machine learning technology is presented. A total of 100 skull shapes were obtained from post-mortem computed tomography data. Homologous models of the whole skull, the cranium only, and the mandible only were created and the coordinates of 40,962 vertices of the models were reduced in dimensionality by principal component analysis (PCA) and partial least squares regression (PLS). Known sexes and the scores of the obtained components were supplied to the support vector machine, and the accuracy rates of sex estimation were obtained by a 10-fold double-looped cross-validation procedure., Lastly, the developed method was applied to six casework skulls with known sexes to validate the power of the estimation. By reducing dimensionality with PLS, remarkably high accuracy rates were obtained in the estimation. The rates reached 100% in all parts examined, while the rates of parts reduced with PCA remained around 90%. Virtual shapes created from very large and small scores of the first and second components of PLS showed the clear sexual dimorphisms that have been proposed by many researchers. The validation results on actual casework skulls were less acceptable than expected, suggesting the necessity of further study with greater numbers of samples for machine learning. The sex estimation method developed here enables us to perform objective identification of skeletal remains required in forensic anthropology field.

Collect the Bones, Avoid the Cones: A Game-Based App for Public Engagement.

Game-based applications (apps) and serious games enable educationalists to teach complex life sciences topics. Gamification principles (i.e. challenges, problem solving, critical thinking) improve learners' motivation and can also help science communicators discuss important scientific subjects and their real-world context in an effective, enjoyable manner. The aim of this study was to design, develop and evaluate a science communication game-based app, entitled Collect the Bones, Avoid the Cones, on human skull anatomy for use in public engagement activities with younger audiences. Specifically, the app contextualised three-dimensional (3D) skull anatomy within a narrative about cycling and helmet safety. The app was tested at the Glasgow Science Centre, with ethical approval from the Glasgow School of Art, to assess its potential pedagogical value, in terms of pre- and post-app knowledge and confidence, and general user evaluation. In total, 50 participants were recruited (mean age 15.6±1.647, range 7-64) with 62% of participants aged 7-12. Usability and educational value were rated highly with 70% of participants agreeing they could use the app without any external instructions and 90% agreeing they understand the anatomy of the skull better after app use. The enjoyability of the game was also positively perceived with 94% of participants agreeing they enjoyed the game. Although there was no statistical significance in pre- and post-app knowledge scores, there was a statistically significant increase in players' confidence relating to skull anatomy (pre-app: 3.00±1.265, post-app: 4.00±1.00, Z=-5.111, p<0.001). These results provide promising insight into the potential of game-based apps for public engagement in anatomical sciences. Future research on how the app influences attitudes towards helmet use in different demographic groups would be valuable in identifying its full pedagogical potential.

Surface Topography-Based Positioning Accuracy of Maxillary Templates Fabricated by the CAD/CAM Technique for Orthognathic Surgery without an Intermediate Splint

Computer-aided design/computer-aided manufacturing (CAD/CAM)-based maxillary templates can transfer a surgical plan accurately only when the template is positioned correctly. Our study aimed to evaluate the positioning accuracy of the CAD/CAM-based template for maxillary orthognathic surgery using dry skulls. After reconstruction of a three-dimensional (3D) virtual skull model, a surface-based surgical template for Le Fort I osteotomy was designed and fabricated using CAD/CAM and 3D printing technology. To determine accuracy, the deviation of the template between the planned and the actual position and the fitness of the template were evaluated. The mean deviation was 0.41 ± 0.30 mm in the medio-lateral direction, 0.55 ± 0.59 mm in the antero-posterior direction, and 0.69 ± 0.59 mm in the supero-inferior direction. The root mean square deviation between the planned and the actual position of the template was 1.21 ± 0.54 mm. With respect to the fitness of the template, the mean distance between the inner surface of the template and the underlying bone surface was 0.76 ± 0.24 mm. CAD/CAM-based templates showed precise positioning and good fitness. These results suggest that surface topography-based CAD-CAM templates can be considered as an alternative solution in replacing the traditional intermediate splints for the transfer of surgical plans.

New information on the skull roof ofProtoichthyosaurus(Reptilia: Ichthyosauria) and intraspecific variation in some dermal skull elements

AbstractA previously unrecognized specimen ofProtoichthyosaurus prostaxalis, LEICT G142.1991, from the Lower Jurassic of Barrow-upon-Soar, Leicestershire, UK, includes an almost complete three-dimensional skull that provides new information on the configuration of the skull roof. The position of the pineal foramen (between the frontals and the parietals) and an elongated internasal foramen in a depression along the midline of the nasals are clearly shown. The maxilla makes up a significant portion of the external naris ventral margin, an unusual character for the genus/species. This reflects intraspecific variation, not evidence of a new taxon. The specimen enables comparisons of skull roof morphology withIchthyosaurusandStenopterygius, two common Early Jurassic taxa. In particular, the position of the pineal foramen is similar toStenopterygius, but distinguishesProtoichthyosaurusfromIchthyosaurus. The lack of a frontal–prefrontal contact and the posteriorly wide nasals distinguishesProtoichthyosaurusfromStenopterygius. We also present a revised reconstruction of the skull roof morphology ofIchthyosaurus. Three additional specimens ofProtoichthyosaurusare referred to the genus: another partial skull, referred toP. prostaxalis, and two isolated forefins, identified by their unique morphology.

An average three-dimensional virtual human skull for a template-assisted maxillofacial surgery.

Although many advances have been made in three-dimensional virtual planning in maxillofacial surgery, facial harmony is still difficult to achieve and is heavily dependent on the surgeon's experience. The aim of the study is to present a method to build up an average three-dimensional virtual human skull to be used as a reference template for bone repositioning and reconstruction during maxillofacial surgical interventions. A total of 20 patients (10 females and 10 males) were selected for the optimal outcome after orthognathic surgery. Postoperative cone-beam computed tomography scans were collected and processed in order to obtain three-dimensional digital models of each skull. For male and female subgroups, the three-dimensional skull models were registered and an average three-dimensional virtual skull model was computed. Deviation color maps were calculated to show differences between each postoperative skull model in the population and the obtained average three-dimensional skull. A clinical use case of genioplasty treatment assisted by the provided average three-dimensional skull template was presented. The overall mean deviation from the average three-dimensional skull model was 1.3 ± 0.6 and 1.6 ± 0.5 mm in male and female subgroups, respectively. For both groups, the greatest deviations were at the area of the mandible, while almost no deviation was found at the zygomatic and orbital areas. In the presented use case, the female average three-dimensional skull model was effectively used for guiding surgical planning. The presented method of obtaining an average three-dimensional virtual human skull may offer the interesting perspective of performing an innovative template-assisted maxillofacial surgery.

Sex Recognition of Skulls in Chinese Uygur.

Objective Logistic regression method was used to establish a multiple regression sex discriminant function to discriminate the complete skull model and the incomplete skull model without frontal bone, occipital bone and mandible of Uygur adults in Turpan, Xinjiang. Methods A total of 117 （60 male and 57 female） three-dimensional skull models were collected by CT. Sixteen cranial measurement indexes were measured and calculated by computer software. The multivariate regression sex discriminant function was established with Logistic regression method and retrospectively tested. Results Among the 16 measurement indexes, except for nose width （x7） and maximum frontal breadth （x13）, the remaining 14 indexes had statistical significance of differences between male and female （P<0.05）. For the discriminant function of complete skull established by eyebrow arch convexity （x4）, mastoid width （x6）, maximum cranial length （x12）, cranial base length （x15）, cranial circumference （x16）, the male and female discrimination accuracy was 90.0% and 94.7%, respectively. For the sex discriminant function of incomplete skull without frontal bone established by mandibular angle width （x10）, mandibular height （x11） and cranial circumference （x16）, the discrimination accuracy of male and female was 85.0% and 84.2%, respectively. For the sex discriminant function of incomplete skull without occipital bone established by the index of eyebrow arch convexity （x4）, the discrimination accuracy of male and female was 80.0% and 73.7%, respectively. For the sex discriminant function of incomplete skull without mandible established by frontal chord （x5） and occipital protrusion angle （x9）, the discrimination accuracy of male and female was 85.0% and 78.9%, respectively. Conclusion The computer software and system developed in our study can achieve sex discrimination of complete skulls and incomplete skulls without frontal bone, occipital bone or mandible.

A new Theriosuchus-like crocodyliform from the Maastrichtian of Romania

We describe a new, small-sized atoposaurid crocodyliform from the Upper Cretaceous (Maastrichtian) of Haţeg Basin, Romania. Aprosuchus ghirai gen. et sp. nov. is represented by a nearly complete three-dimensional skull with articulating mandibles and an associated fragmentary procoelous cervical vertebra that may have belonged to the same subadult individual. The new taxon possesses a heterodont dentition with at least four distinct tooth morphotypes including pseudocaniniform, pseudoziphodont lanceolate, ziphodont lanceolate and ‘low-crowned’ teeth. It differs from Sabresuchus sympiestodon, the other Theriosuchus-like taxon from the same stratigraphic unit, in having less enlarged fang-like teeth, a ‘w’ shaped naso-frontal articulation and extremely large palpebrals strongly fused to the orbital margin. The new taxon shares with other atoposaurids a broad oreinirostral rostrum, a vascular opening on the dorsal surface of postorbital bar, a small antorbital fenestra, a partially septated choanal groove and symmetrically developed lateral compression of maxillary teeth. Other synapomorphies of Aprosuchus are shared by a broader range of taxa including Wannchampsus and paralligatorids. The fossil record indicates that these small, highly specialized crocodylomorphs survived up to the latest Cretaceous by colonizing remote and rather complex insular ecosystems in the western Tethyan archipelago.

A new species of Cyamodus (Placodontia, Sauropterygia) from the early Late Triassic of south-west China

The Triassic eastern Tethyan faunas have continued to yield numerous specimens of marine reptile taxa in recent years. Nevertheless, compared with other sauropterygian clades, the diversity of placodonts in these faunas is low, and remains of this group are relatively rare in the fossil assemblages. Here, we report a new cyamodontoid specimen (ZMNH M8820) from the early Late Triassic of Guizhou, south-west China. This specimen is a nearly complete skeleton lacking only the forelimbs. It is distinct from other known Chinese placodonts as it features a large skull with remarkably enlarged supratemporal fenestrae and a small and less regularly arranged carapace. Interestingly, this new specimen resembles the European Cyamodus more than any Chinese cyamodontoid genera, particularly when considering the dentition and other cranial morphology. However, it differs from known Cyamodus species in some cranial features (e.g. epipterygoid fully ossified, posttemporal fenestra large, dentition derived) and the absence of a separate pelvic shield. Furthermore, based on an updated data matrix of placodonts, our phylogenetic results support the affinity of this new Chinese specimen with European Cyamodus species, and a new species, Cyamodus orientalis sp. nov., is erected here. This new material represents the first reported Cyamodus specimen in the world that preserves a three-dimensional skull with an associated postcranial skeleton and it extends the distribution of this genus into the early Carnian of the eastern Tethys. The existence of Cyamodus, a nearshore taxon, in south-west China at this time reveals greater similarity and more rapid intercommunication than previously known between western and eastern Tethyan vertebrate faunas, although the palaeobiogeographical origin and migration history of Cyamodontidae – and of other clades of placodont reptiles – are still obscure due to the scarcity of material from the northern and southern margins of the Palaeotethys.http://zoobank.org/urn:lsid:zoobank.org:pub:DE6946AD-B4F4-4FC0-AD2F-C5DB2903876D

Sex Determination of Three-Dimensional Skull Based on Improved Backpropagation Neural Network.

Sex determination from skeletons is a significant step in the analysis of forensic anthropology. Previous skeletal sex assessments were analyzed by anthropologists' subjective vision and sexually dimorphic features. In this paper, we proposed an improved backpropagation neural network (BPNN) to determine gender from skull. It adds the momentum term to improve the convergence speed and avoids falling into local minimum. The regularization operator is used to ensure the stability of the algorithm, and the Adaboost integration algorithm is used to improve the generalization ability of the model. 267 skulls were used in the experiment, of which 153 were females and 114 were males. Six characteristics of the skull measured by computer-aided measurement are used as the network inputs. There are two structures of BPNN for experiment, namely, [6; 6; 2] and [6; 12; 2], of which the [6; 12; 2] model has better average accuracy. While η = 0.5 and α = 0.9, the classification accuracy is the best. The accuracy rate of the training stage is 97.232%, and the mean squared error (MSE) is 0.01; the accuracy rate of the testing stage is 96.764%, and the MSE is 1.016. Compared with traditional methods, it has stronger learning ability, faster convergence speed, and higher classification accuracy.

Descriptive anatomy of the largest known specimen of Protoichthyosaurus prostaxalis (Reptilia: Ichthyosauria) including computed tomography and digital reconstruction of a three-dimensional skull.

Ichthyosaur fossils are abundant in Lower Jurassic sediments with nine genera found in the UK. In this paper, we describe the partial skeleton of a large ichthyosaur from the Lower Jurassic (lower Sinemurian) of Warwickshire, England, which was conserved and rearticulated to form the centrepiece of a new permanent gallery at the Thinktank, Birmingham Science Museum in 2015. The unusual three-dimensional preservation of the specimen permitted computed tomography (CT) scanning of individual braincase elements as well as the entire reassembled skull. This represents one of the first times that medical imaging and three-dimensional reconstruction methods have been applied to a large skull of a marine reptile. Data from these scans provide new anatomical information, such as the presence of branching vascular canals within the premaxilla and dentary, and an undescribed dorsal (quadrate) wing of the pterygoid hidden within matrix. Scanning also revealed areas of the skull that had been modelled in wood, clay and other materials after the specimen’s initial discovery, highlighting the utility of applying advanced imaging techniques to historical specimens. Additionally, the CT data served as the basis for a new three-dimensional reconstruction of the skull, in which minor damage was repaired and the preserved bones digitally rearticulated. Thus, for the first time a digital reconstruction of the skull and mandible of a large marine reptile skull is available. Museum records show the specimen was originally identified as an example of Ichthyosaurus communis but we identify this specimen as Protoichthyosaurus prostaxalis. The specimen features a skull nearly twice as long as any previously described specimen of P. prostaxalis, representing an individual with an estimated total body length between 3.2 and 4 m.

Three-Dimensional Skull Model with Vascular Structures for Occipital Expansion in Patients with Developed Occipital Emissary Veins

We report the application of a three-dimensional skull model with vascular structures for occipital expansion in a patient who had developed occipital emissary veins. A 15-year-old boy visited a dentist for orthodontic treatment and was diagnosed with midface hypoplasia. He had undergone a ventriculo-peritoneal shunt at the age of 10 months. On visiting our institution, he was diagnosed with exophthalmos, low visual acuity, reversed bite, and developmental retardation. Moreover, he had sleep apnea and was supported with continuous positive airway pressure at night. Computed tomography and magnetic resonance imaging demonstrated brachycephalus, chronic tonsillar herniation, midface hypoplasia, and well-developed occipital emissary veins. We chose occipital expansion for lowering intracranial pressure and created a three-dimensional skull model with vascular structures and shunt tube. On this model, we wrote scalp incision and craniotomy lines avoiding injury to the veins and shunt tube. The operation was completed using this plan. Patients with syndromic craniosynostosis frequently have developed emissary veins and previous shunt operation. The three-dimensional skull model with vascular structures will be expected to reduce the risks of surgery.

Real-Time Navigation-Guided Drilling Technique for Skull Base Surgery in the Middle and Posterior Fossae.

Objective The usefulness of the bony surface registration method for navigation system image-guided surgery in the lateral or prone position has been reported. This study was performed to evaluate the efficacy of our new real-time navigation-guided drilling technique with bony surface registration for skull base surgery in the middle and posterior fossae. Methods The study included 29 surgeries for skull base tumors that required drilling of the petrous bone between January 2015 and December 2017 in Shinshu University Hospital. A navigation system was used for drilling of the petrous bone as follows: (1) some labyrinthine structures were marked by color in the source image and superimposed on the navigation image on the workstation preoperatively; (2) bony surface registration was performed with a three-dimensional (3D) skull reconstruction model in the operating room; (3) the petrous bone was drilled under navigation guidance with real-time view-through confirmation of 3D color-marked labyrinthine structures with observation under a microscopic operative view. Results Real-time identification of some structures in the petrous bone was performed, and adequate and precise drilling of the petrous bone was achieved without the risk of labyrinthine perforation or stress. Using this method, surgeons do not need to alternate their gaze between the surgical field and the navigation screen. Conclusions Due to the development of bony surface registration, this new technique is useful for drilling petrous bone in the middle and posterior fossa skull base surgeries.

A bird-like skull in a Triassic diapsid reptile increases heterogeneity of the morphological and phylogenetic radiation of Diapsida.

The Triassic Period saw the first appearance of numerous amniote lineages (e.g. Lepidosauria, Archosauria, Mammalia) that defined Mesozoic ecosystems following the end Permian Mass Extinction, as well as the first major morphological diversification of crown-group reptiles. Unfortunately, much of our understanding of this event comes from the record of large-bodied reptiles (total body length > 1 m). Here we present a new species of drepanosaurid (small-bodied, chameleon-like diapsids) from the Upper Triassic Chinle Formation of New Mexico. Using reconstructions of micro-computed tomography data, we reveal the three-dimensional skull osteology of this clade for the first time. The skull presents many archaic anatomical traits unknown in Triassic crown-group reptiles (e.g. absence of bony support for the external ear), whereas other traits (e.g. toothless rostrum, anteriorly directed orbits, inflated endocranium) resemble derived avian theropods. A phylogenetic analysis of Permo-Triassic diapsids supports the hypothesis that drepanosaurs are an archaic lineage that originated in the Permian, far removed from crown-group Reptilia. The phylogenetic position of drepanosaurids indicates the presence of archaic Permian clades among Triassic small reptile assemblages and that morphological convergence produced a remarkably bird-like skull nearly 100 Myr before one is known to have emerged in Theropoda.

The internal cranial anatomy of Romundina stellina Ørvig, 1975 (Vertebrata, Placodermi, Acanthothoraci) and the origin of jawed vertebrates-Anatomical atlas of a primitive gnathostome.

Placoderms are considered as the first jawed vertebrates and constitute a paraphyletic group in the stem-gnathostome grade. The acanthothoracid placoderms are among the phylogenetically most basal and morphologically primitive gnathostomes, but their neurocranial anatomy is poorly understood. Here we present a near-complete three-dimensional skull of Romundina stellina, a small Early Devonian acanthothoracid from the Canadian Arctic Archipelago, scanned with propagation phase contrast microtomography at a 7.46 μm isotropic voxel size at the European Synchrotron Radiation Facility, Grenoble, France. This is the first model of an early gnathostome skull produced using this technique, and as such represents a major advance in objectivity compared to past descriptions of placoderm neurocrania on the basis of grinding series. Despite some loss of material along an oblique crack, most of the internal structures are remarkably preserved, and most of the missing structures can be reconstructed by symmetry. This virtual approach offers the possibility to connect with certainty all the external foramina to the blood and nerve canals and the central structures, and thus identify accurate homologies without destroying the specimen. The high level of detail enables description of the main arterial, venous and nerve canals of the skull, and other perichondrally ossified endocranial structures such as the palatoquadrate articulations, the endocranial cavity and the inner ear cavities. The braincase morphology appears less extreme than that of Brindabellaspis, and is in some respects more reminiscent of a basal arthrodire such as Kujdanowiaspis.