Skull Shape Research Articles

The Scarab Technique for Correction of Late-Presenting Sagittal Suture Craniosynostosis.

Sagittal synostosis (SS) is the most prevalent form of craniosynostosis. It is the premature fusion of the sagittal suture, resulting in a "boat like" skull shape. Early surgical intervention is crucial to prevent complications, yet no standard procedure exists for patients over 12 months old. This study introduces the "Scarab technique", a novel surgical approach for late-presenting SS cases diagnosed after 1 year of age. A single-center, board-approved retrospective review was conducted from May 2017 to June 2020. The Scarab technique was used exclusively for delayed SS diagnosed after 1 year old. A 4cm craniectomy was outlined around the sagittal suture, and vascularized scarab bone flaps attached to the parietal bone vasculature were created. These extension flaps were then lifted for further biparietal and bitemporal expansion, followed by an occipital-type advancement and fixation with resorbable plates and screws. A total of 7 patients with delayed sagittal synostosis diagnosis underwent scarab technique surgery. The majority were male (71%) and Caucasian (43%). Mean surgery age was 2.6 years (SD=1.3), with 3.43-hour average operation time (SD=0.86), 101.4mL estimated blood loss (SD=54.5), 3.85 days in the PICU (SD=0.69), and only 1 patient with a resolved postoperative infection. The Scarab technique is an effective alternative for treating delayed sagittal craniosynostosis, yielding statistically significant improvements in head shape and overall development post-surgery. Further long-term analysis and multicenter comparative studies with alternative techniques are warranted to fully assess its efficacy and outcomes.

Craniosynostosis: Current Evaluation and Management.

Craniosynostosis is characterized by the premature fusion of one or more cranial sutures, which can lead to abnormal skull shape and restricted skull growth. Although most cases are present in isolation, some are associated with genetic syndromes, such as Pfeiffer, Muenke, Couzon, Apert, and others, which increases the complexity of care. Today, a spectrum of surgical options to treat craniosynostosis are available and range from traditional open cranial vault remodeling to newer and less invasive suturectomy-based techniques. Which procedure is offered to a patient depends on not only the specific synostosis pattern but also factors such as patient age, the need for additional procedures or interventions, and evidence of elevated intracranial pressure. Thorough consultations with families to discuss achievable goals for cosmesis and function are essential in providing optimal care to each impacted child.

Features of the parotid gland anatomical parameters in men depending on the shape of the skull

BACKGROUND:Intravital analysis of parotid gland morphometric parameters in the context of various skull shapes is promi­sing, since it allows systematizing the available information on the parotid gland anatomy. AIM:To identify the features of the parotid gland anatomical parameters in men with different skull shapes according to computed tomography and magnetic resonance imaging. MATERIAL AND METHODS:We conducted a retrospective study based on the examination of computer and magnetic resonance tomograms of the heads of 92men. Depending on the skull shape, the study material was divided into groups: dolichocranes (n=30), mesocranes (n=32), brachycranes (n=30); chamecranes (n=19), orthocranes (n=47), hypsicranes (n=26); taipenocranes (n=33), metriocranes (n=30), acrocranes (n=29). Depending on the face shape, three groups were distinguished: euryenes (n=29), mesenes (n=33), leptens (n=40). A morphometric study of the parotid gland was performed with measurement of the sizes in three planes, as well as the volume of the organ using the technique of measuring internal organs’ volume during ultrasound examination. Statistical analysis was performed using nonparametric methods, such as the Kruskal–Wallis test, Mann–Whitney Utest with Bonferroni correction, and Spearman. RESULTS:In men, the sagittal size of the parotid gland significantly increased from brachycranes (4.22cm on the right, 3.99cm on the left) to dolichocranes [4.77cm on the right (p=0.0001), 4.57cm on the left (p=0.0001)]. A decrease in the frontal size of the gland was revealed from brachycranes ([3.43cm on the right, 3.47cm on the left) to dolichocranes [2.49cm on the right (p=0.0001), 2.47cm on the left (p=0.0001)]. With regard to the shapes of the facial skull, a significant difference in the vertical size of the gland was found [in euryenes 6.12cm on the right, 6.18cm on the left; in leptenes 6.98cm on the right (p0.0001), 6.95cm on the left (p0.0001)]. The frontal size value decreased significantly from euryens (3.42cm on the right, 3.53cm on the left) to leptenes [2.51cm on the right (p0.0001), 2.58cm on the left (p0.0001)]. CONCLUSION:In men with different forms of the cerebral skull, determined by the transverse-longitudinal index, the sagittal size of the parotid gland varies significantly; in men, depending on the shape of both the cerebral and facial skull, the frontal size of the gland changes.

Application of Virtual Planning and Three-Dimensional Printing Guide in Surgical Management of Craniosynostosis

This study aims to elaborate on the application of virtual surgical planning (VSP) and 3-dimensional printing guides (3DP) in the surgical management of craniosynostosis and compare their surgical outcomes with traditional surgical planning (TSP). A retrospective review of patients who underwent cranial vault and cranio-orbital remodeling procedures for craniosynostosis was performed. VSP was accomplished by establishing a 3D model from DICOM format CT data. Patients' skull shape were adjusted according to the age-matched standard skull, cutting and reconstruction guides were printed using a 3D printer. The change of anthropometric cranial indices, the so-called degree of correction, before and after the operation was evaluated to assess the surgical outcome. The TSP group serves as the historical control group, and surgical outcomes were compared among propensity-matched patients in the VSP+3DP group. In total, 120 patients with various presentations of craniosynostosis were operated on from 2005 to 2024, and 77 received surgery with VSP+3DP. There were 35 matched pairs. Both had 17 male patients with similar age and body weight. A greater degree of correction was achieved in the VSP+3DP group (9.75% vs. 6.36%, P value=0.016) with less intraoperative blood loss (144.57 mL vs. 296.86 mL, P value<0.001), shorter operation time (335.23 minutes vs. 348.34 minutes, P value=0.501), and hospital stay (10.31 days vs. 12.63 days, P value=0.009). With virtual surgical planning and 3D printing guides, precise preoperative planning, efficient intra-operative correction of cranial deformity, and objective surgical outcome assessment are achieved in craniosynostosis operations.

Three-dimensional cranial suture morphometric changes in young rats during normal growth

The age-based morphometric changes of cranial sutures are not well established, particularly in a quantitative manner. Most prior work utilized planar reslicing approaches to analyze sutures and the quantitative measurements of suture morphometry were limited to a short segment not following the true skull shape. The present study aimed to investigate the age-based morphometric changes of the coronal suture during normal growth of young rats using a novel curved-reslicing approach.Longitudinal in vivo micro-computed tomography (μCT) scans were completed at five time points (7, 9, 11, 16 and 21 weeks of age) during normal growth for 12 Sprague-Dawley rats (six female, six male). Curved-reslicing was performed on μCT slices to generate 11 equidistant cross-sectional images that covered the middle 90 % of skull thickness and the entire length of the coronal suture. The suture linear interdigitation index (LII) and width were measured using a marching algorithm.The average coronal suture LII increased by 15.3 % while the width decreased by 53.5 % at 21 weeks compared to 7 weeks of age, and repeated measures one-way analysis of variance with post-hoc multiple comparisons with Bonferroni adjustment revealed that these differences are statistically significant (p < 0.01). Linear mixed-effect models (LMM) were created for the prediction of rat coronal suture LII and width based on age, relative location through the skull thickness and initial morphometric measurements at the inner surface of the skull. When random effects are considered, the LMM was able to explain up to 97 % and 78 % of variations of suture LII and width, respectively. The presented study has established a novel curved-reslicing method to obtain quantitative 3D information surrounding cranial sutures and demonstrated strong predictive capabilities for suture morphometric changes with age. Future studies considering craniofacial sutures abnormalities will benefit from the presented work through novel methods of studying 3D quantitative morphometry.

Geometric morphometric approach to dental health in an 18th‐ to 19th‐century English infirmary

AbstractThis study evaluated correlations between poor dental health and craniomandibular morphology for the Radcliffe Infirmary population buried between 1770 and 1855. The Radcliffe Infirmary is situated in Oxford, 90 km northwest of London, in what used to be a rural area. The original report for this population observed high prevalence rates of dental caries, antemortem tooth loss (AMTL), and periodontal disease. Industrial societies are acknowledged to have highly processed foods that not only are detrimental to dental health but also require less mastication. This softening of diet is suggested to be the leading influence on the modern morphology of the skull. By using two‐dimensional geometric morphometrics (GM) and linear measurements of the skull, the Radcliffe population was evaluated for the effects of poor dental health and decreased wear on the masticatory structures. High frequencies of AMTL, periodontal disease, and caries and low amounts of dental wear were observed in this sample population. Caries and AMTL showed weak correlations with skull shape and craniomandibular dimensions according to the results of the morphometric analysis and Kendall's tau. Dental wear correlated with a wide bizygomatic breadth and a long narrow skull shape for the males only. Periodontal disease was the only dental health variable not correlated with shape or size. This study confirmed that the Radcliffe population ate a cariogenic diet and suggests that dental wear and pathology weakly correlates with craniomandibular shape and size. This unpredicted finding may be due to the limitations of two‐dimensional shape analysis, a small sample size, and the sampling strategy. Future research is highly encouraged to better understand the consequences of poor dental health for skull morphology.

Evolutionary Links Between Skull Shape and Body Size Suggest Allometric Forces and Selection at Work in a Generalist Group of Lizards.

The vertebrate skull is a complex structure, and studies of skull shape have yielded considerable insight into the evolutionary forces shaping specialized phenotypes in organisms as diverse as bats, frogs, and fossorial animals. Here, we used phylogenetic comparative analyses of CT scans of male skulls from 57 species of Sceloporus lizards to explore patterns of skull evolution in a group of generalist taxa. We found that most interspecific variation is in terms of skull elongation such that some species have long, narrow skulls, whereas others exhibit more compact and robust skulls. We also found strong links to overall body size, with evolutionary shifts to larger bodies being associated with more compact skulls and slower evolutionary rates. This is the opposite of the pattern in most mammals in which larger bodied species have longer snouts, and more like the pattern in frogs in which function has played a more important evolutionary role. Also, unlike other vertebrates, the jaw, anterior, and posterior parts of the Sceloporus skull are largely integrated, having evolved independently of each other only to a limited, albeit significant, degree. Our results emphasize the importance of body size in the evolutionary shaping of the skull and suggest that additional studies of behavioral function in a generalist group are warranted.

Craniosynostosis in Siblings, an Extremely Rare Occurrence: A Case Report.

Craniosynostosis (CS) is the premature fusion of skull sutures, with all sutures except the metopic suture typically fusing in adulthood. Premature fusion constrains brain growth, leading to abnormal skull shape and potential neurocognitive or neurological issues, along with syndromic features in some cases. While CS is rare, its occurrence in siblings is exceptionally uncommon and holds significant academic importance. We report a case of CS in siblings: a 13-month-old boy and his five-and-a-half-year-old sister. Neither parent exhibits craniofacial dysmorphism or signs of increased intracranial pressure (ICP). The younger sibling presents with dolichocephaly and normal neurological, cognitive, and motor development, while the elder sibling exhibits proptosis, midface hypoplasia, and normal developmental milestones. Neither sibling displays limb or systemic anomalies. Imaging studies, including multislice plain CT brain with 3D skull reconstruction and MRI, revealed multiple suture closures. The younger sibling has complete sagittal suture closure with partial closure of other sutures, while the elder sibling shows multisutural CS. Ophthalmologic evaluations and developmental assessments excluded increased ICP and systemic issues. Most CS cases follow an autosomal dominant inheritance pattern, making this case particularly significant. CT with 3D skull reconstruction remains the diagnostic gold standard. Management aims to preserve cosmetic appearance and prevent complications from increased ICP. Treatment options range from conservative follow-up to surgical interventions, including endoscopic suturectomy, open craniotomy, and distraction osteogenesis, depending on the presence of neurocognitive issues or elevated ICP. Both siblings currently show normal neurological, cognitive, and motor development without increased ICP, emphasizing the need for ongoing monitoring to identify new developments or recurrence after treatment. Differential diagnoses, such as deformational plagiocephaly, must also be considered in such cases.

Diagnostic and treatment possibilities in the management of positional plagiocephaly.

Positional plagiocephaly, characterized by an asymmetric skull shape, is the most common craniofacial malformation in infancy. Associated risk factors include apreference for the supine position, first and assisted delivery, multiple pregnancy, prematurity, and congenital muscular torticollis. The diagnosis is established by clinical and anthropometric examinations. In the case of moderate or severe deformity, three-dimensional optical scanning enables adetailed depiction of the deformity and provides asafe and noninvasive tool for follow-up. Treatment mainly includes repositioning of the infant, while orthotic therapy is considered in cases of severe deformity. Cranial orthotic therapy is most effective when started between 4and 7months of age. The total duration of orthotic treatment ranges from 2to 6months. Although the clinical course of positional plagiocephaly is generally benign and the prognosis favorable, its increasing prevalence has prompted the development of novel diagnostic and therapeutic strategies over the past decade.

Precise localization of the central left frontal cortex in different canine skull types: A comparative study of frameless neuronavigation and external measurement techniques

Repetitive Transcranial Magnetic Stimulation (rTMS), a non-invasive brain modulation technique, has been explored as an additional treatment option for behaviorally disordered dogs. For optimal effectiveness of the rTMS treatment, accurate coil positioning to the stimulation target is pivotal. Frameless stereotactic neuronavigation for the localization of intracranial regions has been established as a reliable targeting method. However, given the varying skull shape and brain structures among dog breeds, divided into mesocephalic, brachycephalic, and dolichocephalic breeds, localizing the rTMS target area, the central left frontal cortex, can be challenging. Previous neuronavigation studies have only investigated its use in mesocephalic breeds of dogs. Because this neuronavigation is based on expensive high-tesla magnetic resonance imaging data, and anesthesia needed for immobilization, a cheaper and reliable localization alternative to broaden the rTMS use in the veterinary field is needed.The objective of this study was twofold. First, the study aimed to evaluate external localization of the central left frontal cortex within the three skull types (retrospective study 1). Then, this external localization method was compared to the conventional frameless neuronavigation technique to check the consistency, focusing on mesocephalic and dolichocephalic breeds (prospective study 2). Thirty-two brachycephalic, thirty-seven mesocephalic and thirty dolichocephalic dogs were included to evaluate the external localization of the central left frontal cortex by external measurement (retrospective study 1, data obtained from previously performed MRI scans). For the second objective, thirty-eight dogs (35 mesocephalic breeds and 3 dolichocephalic breeds) were recruited to compare the external measurement localization method and the localization by neuronavigation (prospective study 2, data extracted from study 1 and former rTMS studies). The first part of this study showed the central left frontal cortex was externally located approximately two-thirds of the total skull length (sagittal length) in meso- and dolichocephalic dogs, at the center of the skull length in brachycephalic dogs, and 0.65–0.70 cm to the left of the cerebral midline for all skull types (retrospective study 1). Using intraclass correlation coefficient (ICC) analysis, the second part of the study showed high consistency between these two methods, for the length of the skull (0.94), the relative position of the left frontal cortex (0.84), and the distance to the cerebral midline (0.69) in mesocephalic and dolichocephalic breeds (prospective study 2). Our findings suggest that the conventional frameless neuronavigation could be replaced by the external localization method in the mesocephalic and dolichocephalic dog breeds, and therefore ultimately reduce anesthesia time and financial burden when applying non-invasive brain modulation techniques like rTMS. More research needs to be conducted for brachycephalic dogs to validate this method in this specific population of dogs.

Ecological shifts underlie parallels between ontogenetic and evolutionary allometries in parrotfishes.

During ontogeny, animals often undergo significant shape and size changes, coinciding with ecological shifts. This is evident in parrotfishes (Eupercaria: Labridae), which experience notable ecological shifts during development, transitioning from carnivorous diets as larvae and juveniles to herbivorous and omnivorous diets as adults, using robust beaks and skulls for feeding on coral skeletons and other hard substrates. These ontogenetic shifts mirror their evolutionary history, as parrotfishes are known to have evolved from carnivorous wrasse ancestors. Parallel shifts at ontogenetic and phylogenetic levels may have resulted in similar evolutionary and ontogenetic allometric trajectories within parrotfishes. To test this hypothesis, using micro-computed tomography (μCT) scanning and three-dimensional geometric morphometrics, we analyse the effects of size on the skull shape of the striped parrotfish Scarus iseri and compare its ontogenetic allometry to the evolutionary allometries of 57 parrotfishes and 162 non-parrotfish wrasses. The young S. iseri have skull shapes resembling non-parrotfish wrasses and grow towards typical adult parrotfish forms as they mature. There was a significant relationship between size and skull shapes and strong evidence for parallel ontogenetic and evolutionary slopes in parrotfishes. Our findings suggest that morphological changes associated with the ecological shift characterizing interspecific parrotfish evolution are conserved in their intraspecific ontogenies.

Three-dimensional imaging in craniofacial surgery: utilization of a novel 3D mobile application to evaluate the surgical outcomes of a skull recontouring procedure for cephalohematoma.

Cranial abnormalities are common birth defects that frequently alter skull shape and appearance. Despite their prevalence, objective quantification of defect severity pre- and posttreatment is limited. The authors evaluated the ability of MirrorMe3D, a novel 3D mobile iPhone application, to measure changes in the contour of the skull for patients undergoing contouring of a calcified cephalohematoma. The heads of two 20-month-old patients with disfiguring right parietal cephalohematomas undergoing a skull recontouring operation were scanned pre- and postsurgery. Four scans of the cranial abnormality were taken throughout the procedure and intraoperative 3D models were generated. Models of the head were overlapped pre- and postsurgery and compared using a depth analyzer built into MirrorMe3D. Depth analysis revealed 6.0-mm and 9.9-mm differences for patients 1 and 2, respectively. Volume analysis revealed 33-cm3 and 85-cm3 differences for patients 1 and 2, respectively. Currently, no standard for quantitative measurement of the surgical outcomes of a skull reconstruction procedure exists. MirrorMe3D provides an efficient method for monitoring patients with simple topographic scans that create accurate models of the head. The authors show the app's ability to capture the severity of a calcified cephalohematoma and quantify the changes in the contour of the skull before and after surgery.

Skull Shape Differences among Myanmar and Adjacent Populations of the House Shrew, Suncus murinus (Mammalia: Eulipotyphla): Insights into Allometry and Phylogenetic Variances Using Geometric Morphometrics

Skull Shape Differences among Myanmar and Adjacent Populations of the House Shrew, Suncus murinus (Mammalia: Eulipotyphla): Insights into Allometry and Phylogenetic Variances Using Geometric Morphometrics

Covariation of Skull and Brain Morphology in Domestic Dogs.

Despite their distinct embryonic origins, the skull and brain are highly integrated. Understanding the covariation between the skull and brain can shed light on anatomical, cognitive, and behavioral traits in extant and extinct species. Domestic dogs offer a unique opportunity to investigate skull-brain covariation due to their diverse skull morphologies and neural anatomy. To assess this question, we examined T2-weighted MRI studies of 62 dogs from 33 breeds, plus an additional 17 dogs of mixed or unknown breeds. Scans were opportunistically collected from a veterinary teaching hospital of dogs that were referred for neurological examination but did not have grossly observable structural brain abnormalities. As the neurocrania of dogs become broader and shorter, there is a significant decrease in the gray matter volume of the right olfactory bulb, frontal cortex, marginal gyrus, and cerebellum. On the other hand, as the neurocrania of dogs become narrower and longer, there is a significant decrease in the gray matter volume of the olfactory bulb, frontal cortex, temporal cortex, amygdala, hypothalamus, hippocampus, periaqueductal gray, cerebellum, and brainstem. Selective breeding for specific skull shapes may impact canine brain anatomy and function.

Automatic localization of anatomical landmarks in head cine fluoroscopy images via deep learning.

Fluoroscopy guided interventions (FGIs) pose a risk of prolonged radiation exposure; personalized patient dosimetry is necessary to improve patient safety during these procedures. However, current FGIs systems do not capture the precise exposure regions of the patient, making it challenging to perform patient-procedure-specific dosimetry. Thus, there is a pressing need to develop approaches to extract and use this information to enable personalized radiation dosimetry for interventional procedures. To propose a deep learning (DL) approach for the automatic localization of 3D anatomical landmarks on randomly collimated and magnified 2D head fluoroscopy images. The model was developed with datasets comprising 800000 pseudo 2D synthetic images (mixture of vessel-enhanced and non-enhancement), each with 55 annotated anatomical landmarks (two are landmarks for eye lenses), generated from 135 retrospectively collected head computed tomography (CT) volumetric data. Before training, dynamic random cropping was performed to mimic the varied field-size collimation in FGI procedures. Gaussian-distributed additive noise was applied to each individual image to enhance the robustness of the DL model in handling image degradation that may occur during clinical image acquisition in a clinical environment. The model was trained with 629370 synthetic images for approximately 275000 iterations and evaluated against a synthetic image test set and a clinical fluoroscopy test set. The model shows good performance in estimating in- and out-of-image landmark positions and shows feasibility to instantiate the skull shape. The model successfully detected 96.4% and 92.5% 2D and 3D landmarks, respectively, within a 10mm error on synthetic test images. It demonstrated an average of 3.6±2.3mm mean radial error and successfully detected 96.8% 2D landmarks within 10mm error on clinical fluoroscopy images. Our deep-learning model successfully localizes anatomical landmarks and estimates the gross shape of skull structures from collimated 2D projection views. This method may help identify the exposure region required for patient-specific organ dosimetry in FGIs procedures.

Assessment of Incomplete Apical Bone Coverage of Maxillary Premolar and Molar Roots Using Cone Beam Computed Tomography in 161 Dogs.

This retrospective study assessed maxillary premolar and molar teeth and identified roots with incomplete apical bone coverage using cone beam computed tomography in 161 dogs. The associated dorsal anatomic sites that the roots communicated with were the ventral nasal meatus, maxillary recess, infraorbital canal, and pterygopalatine fossa. The study found that all roots of the maxillary premolar and molar teeth have the potential for incomplete apical bone coverage, with 26.7% having incomplete apical bone coverage. No significant association with sex was found. A significant association with weight was found, and this lowered with increasing body weight. Facial index, as a determinate of skull shape, was found to be significant in only 35.7% of roots in univariate and 14.2% of roots in multivariate modeling. Knowledge of the anatomy of these roots plays an important role in safe and effective extraction techniques, in reducing iatrogenic trauma, and in understanding the potential local effects of periodontal and endodontic disease.

Investigating the Life Expectancy at Birth of Companion Dogs in Portugal Using Official National Registry Data.

This study aimed to provide a comprehensive picture of the life expectancy of dogs in Portugal, focusing on the impact of diverse factors including breed, sex, size, and skull shape. The final dataset, gathering data from the national registry database, consisted of 278,116 dogs with confirmed deaths. The mean lifespan at birth for all the dogs was around 8.91 years, with the female dogs tended to have a similar lifespan to male dogs. The analysis of life expectancy at birth for the 20 most common non-Portuguese breeds and 10 Portuguese breeds revealed that Yorkshire Terriers had the highest life expectancy (10.89 years) and French Bulldogs the lowest (6.27 years). Size and cephalic index were found to be influential factors, with large brachycephalic breeds exhibiting shorter life expectancies and smaller, mesocephalic breeds experiencing longer lifespans. Additionally, the cephalic index had a more substantial impact on life expectancy compared to body size. These findings enhance the understanding of the factors influencing canine longevity and aid in developing strategies to improve the health and lifespan of companion dogs.

Discrepancies Between Objective and Subjective Outcomes of and Quality of Life During Molding Helmet Therapy for Cranial Deformities.

Positional skull deformities have been on the rise for decades and can be treated with molding helmets in early childhood. Parents often fear later cosmetic stigmatization, but also a reduced quality of life (QoL) during treatment. The aim of this study was to examine therapy results in our patient collection from a new perspective. Cranial vault asymmetry (CVA), cranial vault asymmetry index (CVAI), and cranial index (CI) were compared before and after molding helmet therapy. Correction was defined by a decrease in CVA <3.5mm and CI <90%. Subjective therapy outcome, side effects and QoL from the parents' perspective were determined using a questionnaire. There were 25 patients included. Differences between pretherapeutic and posttherapeutic CVA, CVAI, and CI were significant ( P <0.01). An objective correction according to the defined values was observed in only 12% of cases. However, 76% of parents stated that their child's skull shape was normal after therapy. There were 60 side effects reported in 23 cases. The QoL of 21 children was assessed as unimpaired during helmet therapy. Even though complete normalization was rarely observed, the parameters were significantly different after therapy, and subjective reduction in skull deformity was common.

Exploring Skull Shape Variation and Allometry Across Different Chicken Breeds

This study investigates skull shape variation and allometry among three different chicken breeds: Broiler, Lohman Brown, and Leghorn. Geometric morphometric analysis was employed to analyze skull morphology, focusing on facial bones and the neurocranium. The study aims to understand how skull shape differs between these breeds and how it relates to size variation. Results show significant differences in skull morphology among the chicken breeds. Broiler chickens exhibit a distinct skull shape, characterized by a more rounded head and a higher neurocranium compared to the other breeds. In contrast, Lohman Brown and Leghorn chickens show similarities in skull shape, with a more elongated appearance. Broiler chickens were found to be the smallest among the breeds studied, with statistical analysis confirming their distinguishability based on centroid size. In contrast, Lohman Brown and Leghorn chickens exhibited similar sizes, with no significant difference between them. Allometric analysis reveals that skull shape changes with size, particularly in the neurocranium and facial bones. These findings suggest that evolutionary adaptations and breeding practices have influenced the skull morphology of these chicken breeds. Overall, this study provides insights into the skull shape variation and allometry of different chicken breeds, highlighting the importance of considering both genetic and environmental factors in understanding morphological diversity in poultry.

New insights into the early morphological evolution of sea turtles by re-investigation of Nichollsemys baieri, a three-dimensionally preserved fossil stem chelonioid from the Campanian of Alberta, Canada

The early evolution of Pan-Chelonioidea (sea turtles) is poorly understood. This is in part due to the rarity of undeformed skulls of definitive early stem chelonioids. In this work, we redescribe the holotype of Nichollsemys baieri using µCT scans and segmentations of the skull. This fossil is the best 3D preserved skull of any Campanian sea turtle, and includes partial “soft tissue” preservation. Nichollsemys is morphologically similar but clearly distinct from Toxochelys spp., and both show a mosaic of plesiomorphic and derived chelonioid features. The internal cranial anatomy documents the presence of derived characters in Nichollsemys baieri that are absent in Toxochelys spp., such as the loss of the epipterygoids and the rod-like shape of the rostrum basisphenoidale. Among the numerous plesiomorphic characters is the presence of a splenial bone, which was unnoticed before. An updated phylogenetic analysis retrieves Nichollsemys baieri as a non-protostegid early stem chelonioid in a slightly more crownward position than Toxochelys latiremis. Our phylogeny includes macrobaenids and protostegids as pan-chelonioids, and we find unorthodox results for dermochelyids. Thus, although Nichollsemys baieri provides important new insights into the early morphological evolution of sea turtles, much work remains to be done. As a completely 3D preserved specimen, we included Nichollsemys baieri into a recent landmark-based skull shape dataset of turtles. Morphospace analysis reveals an intermediate position between cryptodires and crown chelonioids. Based on these data, we also predict that Nichollsemys baieri was still capable of neck retraction, constraining the loss of this trait to more crownward pan-chelonioids.