Skull Shape Research Articles

How to tuna fish: constraint, convergence and integration in the neurocranium of pelagiarian fishes.

Morphological evolution of the vertebrate skull has been explored across a wide range of tetrapod clades using geometric morphometrics, but the application of these methods to teleost fishes, accounting for roughly half of all vertebrate species, has been limited. Here we present the results of a study investigating three-dimensional morphological evolution of the neurocranium across 114 species of Pelagiaria, a diverse clade of open-ocean teleost fishes that includes tuna and mackerel. Despite showing high shape disparity overall, taxa from all families fall into three distinct morphological clusters. Convergence in shape within clusters is high, and phylogenetic signal in shape data is significant but low. Neurocranium shape is significantly correlated with body elongation and significantly but weakly correlated with size. Diet and habitat depth are weakly correlated with shape, and non-significant after accounting for phylogeny. Evolutionary integration in the neurocranium is high, suggesting that convergence in skull shape and the evolution of extreme morphologies are associated with the correlated evolution of neurocranial elements. These results suggest that shape evolution in the pelagiarian neurocranium reflects the extremes in elongation found in body shape but is constrained along relatively few axes of variation, resulting in repeated evolution towards a restricted range of morphologies.

Comparison of skull growth in two ecosystem modifiers: beavers Castor canadensis (Rodentia: Castoridae) and muskrats Ondatra zibethicus (Rodentia: Cricetidae)

Beavers and muskrats are semi-aquatic, generalist herbivorous rodents regarded as invasive in southern South America, with high impacts on the ecosystem. They share some morphological characters of the skull, but different body sizes and phylogenetic history, showing evident shape differences in young and adult skulls during the development in both species. Considering their similar ecological specializations, skull shape could be achieved through different or similar patterns of allometric growth during ontogeny. We analyzed quantitatively the ontogenetic series including 94 specimens of beavers and muskrats and performed multivariate and bivariate analyses considering 20 linear measurements. Our main results from the different approaches suggest high differences in the ontogenetic trajectories of beavers and muskrats, implying disparity in the muscular, functional, and structural conditions of the skull of both species. These differences reflect that although skulls might undergo similar mechanical stress, it is possible to reach a cranial morphology compatible with the similar behavioral and ecological specializations between both species from patterns of skull development that are markedly different.

Morphological relationships among populations support a single taxonomic unit for the North American Gray Wolf

Abstract The Gray Wolf (Canis lupus) is viewed as one of the most diverse mammal species. In North America, the diversity of its forms is debated, with views conflicting on subspecies designation. The present study aimed to reinvestigate the skull morphometric variation among North American populations while attempting to unveil underlying causal factors. A large sample of vouchered museum skulls, collected from 12 ecogeographical populations spanning the North American range of the species, was examined and 21 craniodental characters were measured. Skull shape showed within-population variations but provided evidence for a high morphological affinity among populations. Allometric analyses also pointed to similar evolutionary paths among populations. However, significant size-related differentiation was revealed within and among populations. Skull size could be related to three insulin-like growth factor-1 gene (IGF-1) alleles. Ecological conditions that should determine prey type and availability accounted for most of the skull size variation. In contrast, no evidence of geographical isolation of populations was detected. The results support the existence of a single morphological pool of North American gray wolf populations that could be equated with one taxonomic unit. This study raises again the question of the diversity of forms in this species in North America and calls into question the validity of previously recognized species and subspecies based on genetics and morphology.

Seeing through the eyes of the sabertooth Thylacosmilus atrox (Metatheria, Sparassodonta)

The evolution of mammalian vision is difficult to study because the actual receptor organs—the eyes—are not preserved in the fossil record. Orbital orientation and size are the traditional proxies for inferring aspects of ocular function, such as stereoscopy. Adaptations for good stereopsis have evolved in living predaceous mammals, and it is reasonable to infer that fossil representatives would follow the same pattern. This applies to the sparassodonts, an extinct group of South American hypercarnivores related to marsupials, with one exception. In the sabertooth Thylacosmilus atrox, the bony orbits were notably divergent, like those of a cow or a horse, and thus radically differing from conditions in any other known mammalian predator. Orbital convergence alone, however, does not determine presence of stereopsis; frontation and verticality of the orbits also play a role. We show that the orbits of Thylacosmilus were frontated and verticalized in a way that favored some degree of stereopsis and compensated for limited convergence in orbital orientation. The forcing function behind these morphological tradeoffs was the extraordinary growth of its rootless canines, which affected skull shape in Thylacosmilus in numerous ways, including relative orbital displacement.

COMPARATIVE CHARACTERISTICS OF THE LINEAR DIMENSIONS OF VARIOUS FORMS OF THE FACIAL SKULL

For many years, radiography has traditionally been the main method for studying of the morphology of the facial skull and identifying craniofacial deformities, however, it is difficult to assess the typical variability of the linear dimensions of the facial skull on radiographs due to the many overlapping shadows of anatomical structures. Comparison of the results of craniometry of macerated skulls, radiographs and spiral computed tomography shows that multislice computed tomography in some cases can be the best alternative to conventional radiography and other methods of studying the facial skull. The purpose of the study was to conduct a comparative analysis of the linear dimensions of the facial skull with its various forms according to multislice computed tomography. Tomograms of 105 patients with different facial skull shapes were studied. Tomography was performed on a «Brilliance 64 Slice» multislice spiral X-ray computed tomography scanner at the Department of Magnetic Resonance and X-ray Computed Tomography of the Rostov State Medical University for suspected cerebrovascular pathology. The obtained images were analyzed using axial, multiplanar, and shadow density surface reconstructions in various projections. Measurements were made using a standard digital ruler of a computer tomography workstation, typical features of the linear dimensions of the facial skull were evaluated using the fan-beam method. In the studied group of individuals, the predominance of euryenes (46.7%, n=49) over mezenes (37.2%, n=35) and leptens (18.1%, n=9) was revealed. A comparative characteristic of the linear dimensions of the facial skull on spiral computed tomograms is described. According to the results of the study, the linear dimensions of the facial skull on the right dominate in leptens and euryenes, on the right in sections of the upper fan on the right, and on the left in sections of the lower and lateral fans. A left-sided asymmetry of the linear dimensions of the facial skull in sections of the lower fan, which is characteristic of mezenes, was established, while a right-sided asymmetry was found for euryenes and leptens. The data obtained as indicators of normal craniometry can be used in clinical practice by radiologists, plastic surgeons, maxillofacial surgeons, as well as in anthropology and forensic medicine.

Skull variation in different breeds sheep from Balkan countries

The Balkan Peninsula region has a very diverse agricultural and livestock tradition, and almost every country has its own local breed of sheep. Different breeds of sheep and different breeding traditions, despite the small geographical distance, determine the morphological and morphometric variability among animal breeds. In this study, this morphological diversity among the skulls of sheep breeds of some countries in the Balkan region was examined by the geometric morphometric method. 2D images of 86 sheep skulls from five different countries were analyzed from the dorsal view.Sixteen landmarks were used. The Bardhoka and the Ivesi breed have the broadest distributions of skull shape amongst the sheep breeds. The Ruda sheep is the most morphologically conservative. The sheep from Turkey (Ivesi) and Kosovo (Bardhoka) seem to differ mainly from sheep from other Balkan countries. Bardhoka and Ruda differ most from each other (p < 0.0001). The next biggest differences were between Ivesi and Ruda (p < 0.0011) and between Bardhoka and Sharri sheep (p < 0.0016). The sheep breeds Dubska and Lara e Polisit differ the least from each other. Geometrics morphometric analysis is a useful tool to detect differences in the shape of the skull of different sheep breeds and can therefore be used successfully for taxonomic purposes.

The Paediatric Vault Score (PVS)-A Novel Scoring Tool for Prioritisation of Surgical Management of Craniosynostosis Patients.

Craniosynostosis is the premature fusion of the skull sutures, resulting in abnormal skull shape and volume. Timely management is a priority in avoiding raised intracranial pressure which can result in blindness and neurodevelopmental delay. Due to the COVID-19 pandemic, theater access was reduced. A risk stratification scoring system was thus devised to score patients attending surgery and aid in prioritization according to surgical need. The authors present the Paediatric Vault Score (PVS), which can also be customized to each unit's individual protocols. Ten patients on the waiting list were randomly selected and their clinical information was summarized in uniform anonymized reports. Six craniofacial consultants were selected as assessors and given 1 week to independently rank the patients from 1 to 10. Each scorer's ranking was verified against the PVS template and concordance was analyzed using the Kendall tau correlation coefficient (KT). Three cycles of the scoring process were carried out. Improvements were made to the scoring tool following cycle 1. Cycle 1 revealed 2 clinicians to be concordant with the PVS system and 4 to be discordant. Cycle 2 revealed all 6 clinicians to be concordant, with a mean KT score of 0.61. The final cycle revealed all 6 clinicians to be concordant, with a mean KT score of 0.70. Four scorers increased their concordance once the scoring sheet was introduced. Kendall's correlation of concordance calculated the interrater reliability to be 0.81. The PVS is the first known vault scoring system to aid in risk stratification and waiting list prioritization.

Latitudinal gradients in the skull shape and assemblage structure of delphinoid cetaceans

AbstractWithin delphinoid cetaceans, snout shape is significantly correlated to diet, with long-snouted raptorial-feeding predators preying on smaller and more agile prey than shorter-snouted species. Although there have been several studies into longirostry from a functional perspective there have been no quantitative analyses of spatial variation in skull shape or how the pattern in skull shape morphospace occupation varies between assemblages. Here we analyse the cranial morphological variation of Delphinoidea assemblages. Firstly, we calculate mean and Gi* hotspot statistics of skull shape across the world’s oceans. We find that tropical and subtropical assemblages exhibit higher average measures of longirostry. This pattern is likely caused by differences in the availability of certain prey types in warmer and cooler environments. Secondly, we calculate mean pairwise distance as well as mean nearest taxon distance in functional traits between the members of 119 unique delphinoid assemblages. There was a trend for low latitude assemblages to exhibit greater overdispersion in PC1 (snout length) compared those from high latitudes. Our results suggest that ocean temperature is influential in determining the diversity, range limits and assemblage structure of delphinoid cetaceans.

Dogs (14–18th centuries AD) from Nadym Gorodok archaeological site (Western Siberia, Russia): Morphology and function

AbstractAn osteological collection of dogs from an aboriginal population settlement (Nadym Gorodok) in Western Siberia is described in this work. There were numerous bones (more than 1600) well preserved in the permafrost cultural layer, including almost complete skeletons of dogs of various ages. Craniological characteristics and reconstructions of the size and functions of the aboriginal dog were studied. The analysis of the finds showed that there was a large number of dogs in Nadym Gorodok in the 14–18th centuries AD. Dogs were bred on site in the settlement. During the 4 centuries, middle‐size dogs of the same build were kept in Nadym Gorodok. In size and general skull shape, the dogs were similar to the modern laika breed. The dogs were used mainly for hunting. During a hunt, dogs stalked prey and pulled sledges as a draft animal. There were no herding dogs.

Examination of Shape Variation of the Skull in British Shorthair, Scottish Fold, and Van Cats.

A variety of skull shapes are frequently used for discrimination between animal species, breeds, and sexes. In this study, skulls of three different breeds of cats were examined by the geometric morphometric method, with the aim of revealing skull shape differences. For this purpose, 27 cats (6 British Shorthair, 7 Scottish Fold, and 14 Van cats) were used. The skulls of cats were modeled by computed tomography. Geometric morphometrics was applied using dorsal (8 landmarks, 63 semilandmarks) and lateral (8 landmarks, 63 semilandmarks) skull projections on these models. Centroid size differences between the breeds were statistically insignificant. However, the differences in shape were statistically significant for both the dorsal view and lateral view. Shape variation was less in the British Shorthair than in other breeds. Shape differences generally occurred around the orbit. In the skull of Scottish Folds, the orbit was situated more caudally than in other breeds. The British Shorthair had the largest orbital ring. In dorsal view, the Scottish Fold had the largest orbital diameter. The orbital ring of Van cats was smallest in both dorsal and lateral views. In the canonical variate analysis, it was seen that the breeds were separated from each other. The shape difference in the skull between different cat breeds could be revealed by geometric morphometrics. The results of this study provide useful information for taxonomy.

Geographic variation in select species of the bat genus Platyrrhinus

The taxonomy of Neotropical bats is constantly changing, with new species being described and junior synonyms elevated, while other taxa are relegated to junior synonyms or subspecies. The genus Platyrrhinus has followed this trend, with some issues persisting about the current status of its subspecies. Here we evaluate variation in cranial shape and size based on geometric morphometric analyses of Platyrrhinus dorsalis and P. umbratus. P. dorsalis occurs at elevations from sea level to above 2,000 m and is found from southern Panama southward into Colombia and along both slopes of the Andes in Ecuador. P. umbratus occurs at elevations from 400 m to above 3,150 m in the Andean from Colombia south through Bolivia and Caribbean Mountain systems of Venezuela and Colombia. Our analyses did not support the recognition of subspecies in either species. The difference in skull size and shape between populations of P. dorsalis is associated with elevation, suggesting that this species exhibits an altitudinal clinal variation, with individuals being larger in the lower elevation and smaller in higher elevations. In P. umbratus the difference in skull size and shape between populations is associated with a latitudinal cline, with individuals tending to be larger in the northern part of their range. Our analyses did not reveal the existence of secondary sexual variation in P. dorsalis nor in P. umbratus.

Ecomorphology of toothed whales (Cetacea, Odontoceti) as revealed by 3D skull geometry

Extant odontocetes (toothed whales) exhibit differences in body size and brain mass, biosonar mode, feeding strategies, and diving and habitat adaptations. Strong selective pressures associated with these factors have likely contributed to the morphological diversification of their skull. Here, we used 3D landmark geometric morphometric data from the skulls of 60 out of ~ 72 extant odontocete species and a well-supported phylogenetic tree to test whether size and shape variation are associated with ecological adaptations at an interspecific scale. Odontocete skull morphology exhibited a significant phylogenetic signal, with skull size showing stronger signal than shape. After accounting for phylogeny, significant associations were detected between skull size and biosonar mode, body length, brain and body mass, maximum and minimum prey size, and maximum peak frequency. Brain mass was also strongly correlated with skull shape together with surface temperature and average and minimum prey size. When asymmetric and symmetric components of shape were analysed separately, a significant correlation was detected between sea surface temperature and both symmetric and asymmetric components of skull shape, and between diving ecology and the asymmetric component. Skull shape variation of odontocetes was strongly influenced by evolutionary allometry but most of the associations with ecological variables were not supported after phylogenetic correction. This suggests that ecomorphological feeding adaptations vary more between, rather than within, odontocete families, and functional anatomical patterns across odontocete clades are canalised by size constraints.

Abstract IA021: Studies of aging, morphology, and cancer in the domestic dog

Abstract Each of the nearly 450 domestic dog breeds in existence today has a unique history and genetic profile. Early in the domestication process, dogs were bred to perform specific tasks such as herding, guarding and hunting. Later, fanciers developed hundreds of breeds, often displaying variation in body morphology, including shape and size, in addition to coat color, skull shape, leg length, etc. We are interested in understanding the genetic underpinnings of that variation, and applying those results to studies of growth regulation, normal and abnormal behavior and disease susceptibility. Dogs are a naturally-occurring model for many complex human disorders, including cancer. One in two dogs that live to be ten or older will develop cancer in their lifetimes, with most common human cancers occur spontaneously in dogs. This offers unique opportunities to study cancer susceptibility, progression and treatment response. The high rate of single types of cancer in some breeds, such as histiocytic sarcoma in Bernese Mountain Dogs or invasive bladder cancer in Scottish Terriers offers specific advantages for genetic studies that do not exist in human population studies. As with cancer, domestic dogs present interesting opportunities for studies of aging. Surprisingly, small breeds typically live longer than larger breeds, offering the chance to study the interaction between morphology and lifespan. To take advantage of these opportunities, we have assembled the largest and most diverse dataset of dog breeds and other canines to date, with canines originating from six continents, reflecting the extensive phenotypic variation and heritage that coalesce in modern dogs, and identified over 90 million single nucleotide variants. In this presentation we explore the genetics of cancer and aging in dogs, drawing parallels to the human condition. Citation Format: Elaine A. Ostrander. Studies of aging, morphology, and cancer in the domestic dog [abstract]. In: Proceedings of the AACR Special Conference: Aging and Cancer; 2022 Nov 17-20; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2022;83(2 Suppl_1):Abstract nr IA021.

Island Tiger Snakes (Notechis scutatus) Gain a ‘Head Start’ in Life: How Both Phenotypic Plasticity and Evolution Underlie Skull Shape Differences

Island Tiger Snakes (Notechis scutatus) Gain a ‘Head Start’ in Life: How Both Phenotypic Plasticity and Evolution Underlie Skull Shape Differences

The role of cultural traditions in ecological niche partitioning in cetaceans

Ecological niche partitioning is a process that allows organisms to achieve differences in resource use to reduce competition. Niche partitioning is traditionally viewed as a result of modification of genetically inherited traits through the process of adaptive evolution. However, in social animals with developed cognitive abilities, a significant portion of behavioral patterns is transmitted not genetically, but through social learning. Complex sets of behavioral patterns transmitted through social learning are called cultural traditions. The partitioning of ecological niches in cetaceans is most often considered in the context of morphological adaptations: changes in size, skull shape, and the structure of the filtering apparatus. The role of cultural traditions in niche partitioning is still poorly understood, but it is an important and promising area of research, as it provides a novel approach to the ability of animals to change their behavior in order to exploit the environment more efficiently. The main advantage of traditions over genetically inherited behavioral patterns is the ability to change quickly and spread rapidly in a population. Estimating the role of cultural traditions in ecological niche partitioning would highlight the significance of behavior plasticity and social learning in the evolution of animal intelligence. Ecological niche partitioning through the rapidly changing and rapidly spreading behavioral adaptations in the population, allowing to adapt quickly to changes in the environment, could provide a significant evolutionary advantage, which could lead to the development of a relatively high level of intelligence in cetaceans.

Taxonomic position and biogeography of Mus callewaerti, the largest species of the subgenus Nannomys (Rodentia: Muridae)

The Callewaert’s mouse (Mus callewaerti) is shown as an ancient lineage of the African endemic subgenus Nannomys. Described in 1925 as a large-bodied species with proodont (forward pointing) incisors, it was long known only from a handful of localities in Angola and southern Democratic Republic of the Congo. Here, it is revealed identical with a genetically distinctive Nannomys, provisionally called Mus sp. “Nyika” in previous studies and reported from Nyika Plateau (Malawi) and the Angolan Escarpment. The skull shape analysis clearly associated the holotype of M. callewaerti with other specimens ascribed to the species (including the genotyped ones). It also pinpointed diagnostic features distinguishing M. callewaerti from other large bodied Nannomys, especially its sympatric Mus triton, for which the species was repeatedly mistaken. Mus callewaerti is presumably insectivorous and rare or not easy to capture. The divergence between its Malawian and Angolan populations is relatively shallow, dated to 0.32 million years ago, which suggests that at least in the past the species could be widespread. Mus callewaerti is known from grassy, locally moisty habitats. Together with a handful of other rodent taxa it provides evidence of persistence and historic connection of these habitats across the Zambezian region.

NSD1 gene evolves under episodic selection within primates and mutations of specific exons in humans cause Sotos syndrome

BackgroundModern human brains and skull shapes differ from other hominids. Brain growth disorders as micro- (ASPM, MCPH1) and macrocephaly (NFIX, GLI3) have been highlighted as relevant for the evolution in humans due to the impact in early brain development. Genes associated with macrocephaly have been reported to cause this change, for example NSD1 which causes Sotos syndrome.ResultsIn this study we performed a systematic literature review, located the reported variants associated to Sotos syndrome along the gene domains, compared the sequences with close primates, calculated their similarity, Ka/Ks ratios, nucleotide diversity and selection, and analyzed the sequence and structural conservation with distant primates. We aimed to understand if NSD1 in humans differs from other primates since the evolution of NSD1 has not been analyzed in primates, nor if the localization of the mutations is limited to humans. Our study found that most variations causing Sotos syndrome are in exon 19, 22 and 10. In the primate comparison we did not detect Ka/Ks ratios > 1, but a high nucleotide diversity with non-synonymous variations in exons 10, 5, 9, 11 and 23, and sites under episodic selection in exon 5 and 23, and human, macaque/colobus/tarsier/galago and tarsier/lemur/colobus. Most of the domains are conserved in distant primates with a particular progressive development from a simple PWWP1 in O. garnetti to a complex structure in Human.ConclusionNSD1 is a chromatin modifier that suggests that the selection could influence brain development during modern human evolution and is not present in other primates; however, nowadays the nucleotide diversity is associated with Sotos syndrome.

Population Structure and Morphological Pattern of the Black-Spotted Pond Frog (Pelophylax nigromaculatus) Inhabiting Watershed Areas of the Geum River in South Korea

Black-spotted pond frogs (Pelophylax nigromaculatus), widely distributed in East Asia, can be suitably used for the study of population genetic patterns and ecosystem monitoring. To systematically manage, conserve, and study this species, it is necessary to understand its habitat range. We analyzed the genetic and morphological range of black-spotted pond frog populations within a watershed of the Geum River, one of the main rivers in South Korea. We genotyped the frogs based on seven microsatellite loci and defined the skull shape based on landmark-based geometric morphometrics. One watershed area was divided into 14 sub-watershed areas, the smallest unit of the Geum River basin. The genetic structure of frogs among the 14 sub-watershed areas did not differ significantly, nor was correlated with geographic distance. Therefore, frogs within these watershed areas constitute a single population. Morphologically, they differed between some sub-watershed areas, but morphological distance did not correlate with genetic distance but rather with geographic distance. This morphological change differs depending on the environmental gradient rather than the genetic structure. As a single population, frogs in this watershed area need to be managed in an integrated way. We suggest that the identification of response and adaptation by population genetics must be compared across and beyond the watershed range.

Apert Syndrome with Agenesis of the Corpus Collosum - Case Report

Abstract Apert syndrome (Acrocephalosyndactylia type 1) belongs to the group of extremely rare congenital dysmorphic syndromes. It is characterized by craniostenosis with very early fusion of the skull and / or cranial base sutures, facial hypoplasia, symmetrical syndactyly of the fingers and toes and other systemic malformations. Multiple CNS abnormalities are common, but simultaneous occurrence of Apert syndrome and agenesis of corpus callosum is estimated about 10%. We present a male patient born after first, normal and controlled pregnancy and term, naturally birth, in which the Apert syndrome was diagnosed, based on the clinical presentation of the skull and face and syndactyly of fingers and toes. Neurological examination established generalized hypotonia and aggravated provocation of the primitive reflexes. Neurosonography showed complete agenesis of the corpus callosum, which makes this case a rare form of this syndrome. The head X-rays showed turricephalic skull shape and suture’s synostoses, which is demonstrated in more detail at computed tomography finding. The hands and feet X-rays showed bone synostosis of fingers and toes. The video-electroencephalogram recorded intermittent depression of electrocortical activity. There was conducted the multidisciplinary examination in order to examine the possibility of reconstructive and plastic surgical correction of the anomalies. The neurodevelopmental disorders in patients with Apert syndrome can be manifested by a variety of congenital malformations, but considering its rare occurrence, the significance of these abnormalities remains unknown.

Covariation of brain and skull shapes as a model to understand the role of crosstalk in development and evolution.

Covariation among discrete phenotypes can arise due to selection for shared functions, and/or shared genetic and developmental underpinnings. The consequences of such phenotypic integration are far-reachingand can act to either facilitate or limit morphological variation. The vertebrate brain is known to act as an "organizer"of craniofacial development, secreting morphogens that can affect the shape of the growing neurocranium, consistent with roles for pleiotropy in brain-neurocranium covariation. Here, we test this hypothesis in cichlid fishes by first examining the degree of shape integration between the brain and the neurocranium using three-dimensionalgeometric morphometrics in an F5 hybrid population, and then genetically mapping trait covariation using quantitative trait loci (QTL) analysis. We observe shape associations between the brain and the neurocranium, a pattern that holds even when we assess associations between the brain and constituent parts of the neurocranium: the rostrum and braincase. We also recover robust genetic signals for both hard- and soft-tissue traitsand identify a genomic region where QTL for the brain and braincase overlap, implicating a role for pleiotropy in patterning trait covariation. Fine mapping of the overlapping genomic region identifies a candidate gene, notch1a, which is known to be involved in patterning skeletal and neural tissues during development. Taken together, these data offer a genetic hypothesis for brain-neurocranium covariation, as well as a potential mechanism by which behavioral shifts may simultaneously drive rapid change in neuroanatomy and craniofacial morphology.