Preliminary study on cranial measurements and sexual dimorphism in skull bones of gaur (Bos gaurus gaurus, Smith 1827).

Cranial measurements have been widely used in various studies in wildlife sciences, ranging from understanding predator ecology to wildlife forensics. However, detailed description of morphometry and sexual dimorphism of the skull of gaur Bos gaurus gaurus is lacking. The present study was undertaken to determine the sexual dimorphism based on the cranial measurements of gaur. A total of 12 individual gaur skulls of male (n = 6) and female (n = 6) were studied in the field from the naturally deceased animals between January 2018 and December 2021 in different ranges of Bandhavgarh tiger reserve (BTR), Madhya Pradesh, India. The skull measurements were analysed using univariate and multivariate statistics to determine whether cranial dimensions could be used to differentiate male and female skulls reliably. A total of 43 morphometrical parameters grouped into nine indices were calculated. Select morphometrical parameters viz PL, GFL, AKI, LBB, LFB, GBEE, GBAN, BPOP and GTCH were significantly different (p < 0.05) between sexes, whereas GBAN were significantly higher in female skulls. The measurements demonstrated that the skull of the gaur was dolichocephalic as the profile length and the otion to otion breath in both male and female were <75% of the length. Overall, 28 linear measurements of both the sexes were statistically significant (p < 0.05; <0.01). The calculated indices revealed that the foramen magnum index in the female gaur were significantly higher. In calculated cranial indices the facial index (a) was higher in female and facial index (b) were higher in males. The two important parameters, facial breadth in facial index (a) and the greatest breadth in facial index (b) were positively correlated, though facial index (a) was statistically not significant between the sexes. The greater inner length of the foramen magnum in female skull resulted in foramen being oval whereas it was circular in males. These parameters were decisive for sexual dimorphism, skull comparison and craniological studies. This study ascertained that the frontal index and skull index had no significant influence and were not good indices for discriminating skulls between male and female. Based on the Principal Component Analysis, it was found that skull of male and female gaurs exhibits differences in cranial morphology viz. cranial profile length or total length (PL) and the least inner height of the temporal groove (LIHT). The findings of the present study provide baseline information on various craniometrical measurements of skull of gaur, indices and parameters for sex identification that can be effectively used in understanding sex biased predation ecology, provide base line information to describe variation across its geographic range, and in identifying skulls recovered in wildlife offence cases.

Three-dimensional modelling and morphometric analysis of skull of badger (Meles meles) with computed tomography images.

BACKGROUND: Morphometric measurements help to understand the skull morphology in different animal species, detect skull deformations and figure out their causes. OBJECTIVES: The aim of this study is to make a three-dimensional (3D) modelling of the badger skull using computed tomography, to show its anatomical structures and to reveal the morphometric measurement values. METHODS: Skull measurements were carried out using a digital calliper at 27 measurement points based on metric measurement points. After the scanned images were stored in Digital Imaging and Communications in Medicine format, they were transferred to MIMICS 20.1 (The Materialize Group) programme and 3D models the skulls were created. The surface area and volume values of the skulls were calculated on these models. RESULTS: The volume and surface area parameters were expressed as mean ± SE. Four different indices were calculated using osteometric measurements. Statistical analyses were made by determining the mean value and standard deviation of the examined properties and the correlation coefficients among these properties. In the metric measurement points taken as a basis, the longest measurement in the skulls was the total length and its mean value was 124.60 ± 0.64 mm. The shortest measurement was the breadth dorsal to the external auditory meatus, and its mean value was 6.75 ± 0.24 mm. CONCLUSIONS: Consequently, statistical differences in the craniometric values of badgers' skulls were determined by using CT and 3D modelling software. In addition, it was concluded that the badger skull can be easily distinguished from other carnivore species by carrying out morphometric measurements.

Comparison of craniometric measurements of New Zealand rabbit (Oryctolagus cuniculus L.) using three-dimensional scanner with digital calliper measurements: A methodological study.

As technology has developed in recent years, the use of three-dimensional (3D) scanners and printers has become widespread in the medical field. However, since this field is new, all kinds of methodological and experimental related studies gain importance. This study aimed to identify the differences between the calliper measurements by determining the craniometric data on the models constructed by scanning the crania of New Zealand Rabbits (Oryctolagus cuniculus L.), preferred as experimental animals, with a three-dimensional scanner. Therefore, a total of 12 New Zealand rabbits including 6 females and 6 males were used. After the crania that comprised the study material were macerated, they were subjected to 3D scanning. After the scanning process was completed, they were craniometrically measured both on the scanned models and by using a digital calliper. Analysis of the craniometric data of the 3D scanner showed that there was a difference between sexes at the level of p < 0.05 in widest length between the external acoustic meatus (WLBEAM), skull width and Foramen magnum height (FMH) parameters and cranial index data, and at the level of p < 0.001 in the largest nasal width (LNW) parameter. A statistical difference was found between sexes in frontal length, WLBEAM, LNW and FMH parameters and cranial index values in craniometric data collected with the digital calliper (p < 0.05). Consequently, the data collected in this study were found to be close to each other in both methods, suggesting that the 3D scanner may be used in morphometric studies.

Radiological examination of the skull of Siirt-coloured mohair goat, Romanov and Hamdani sheep.

The skull is a vitally important complex structure formed by the combination of many bones. Craniometric studies are performed with various imaging methods to determine morphometric characteristics in animals. One of these methods is radiography. In our study, skulls of 14 Hamdani sheep, 20 Siirt-coloured mohair goats and 20 Romanov sheep breeds were used. Skull sections were taken with a computed tomography device and saved in DICOM format. Nine separate measurements and six index calculations were made from the images. In the study, firstly, the gender difference was ignored and the similarities and differences between the species were recorded. In addition, gender differences were determined statistically, without making any distinction between species. Correlation analysis was performed to compare measurement parameters between animal species. As a result of the study, the highest skull length (SL) and cranial length (CL) values were determined in the Siirt-coloured mohair goat. It was determined that the difference between Romanov sheep and Siirt-coloured mohair goat in CL parameter was not statistically significant (p > 0.05). In addition, a statistically significant difference was observed between the Romanov sheep breed and the Hamdani sheep breed (p < 0.01). The external length of the cranium (ELC) measurement parameter was found to have a statistically significant difference in three animals (p < 0.01). According to the results of the correlation analysis, the highest correlation value was determined between cranial width (CW) and CL parameters (r = 0.920). When the species difference was ignored, and the statistical difference of the internal height of the cranium (IHC) parameter was found to be significant between female and male animals (p < 0.05). In addition, it was determined that SL, CW and internal cranium index (ICI) parameters had a significant difference depending on sex (p < 0.01). It is foreseen that the obtained data can be used in sciences such as zoo archaeology, anatomy, surgery and forensic medicine.

Morphometric analysis of the skull of Hamdani sheep via Three-Dimensional modelling.

The aim of the present study was to determine the craniometric characteristics of the crania of Hamdani sheep, one of local breeds of Turkey, by using computed tomography (CT). In the study, 13 (six female and seven male) skulls were used. After CT images of the skulls were taken, their three-dimensional models were created by MIMICS 20.1 (The Materialise Group, Leuven, Belgium) program. Thirty-eight craniometric measurements were taken over the models created and nine indices were calculated by using these measurements. All the characteristics examined were expressed as mean ± SE. In the study, statistically significant differences were found between females and males in terms of greatest neurocranium breadth, facial breadth, greatest palatal breadth (p < 0.05) and height of the foramen magnum (p < 0.01) parameters. No statistically significant difference was observed between the sexes in the calculated index values (p > 0.05). In conclusion, it is thought that the findings obtained from the study will contribute to the zooarchaeology and sheep taxonomy of Mesopotamian region.

Orthodontic Inclined Plane Application Using a Visible Light Cure Acrylic Material for Treatment of Linguoverted Mandibular Canine Teeth.

Malocclusion is a common problem in dogs. Linguoverted canine teeth (class I malocclusion) can cause palatal defects, oronasal fistulae, dental wear, and periodontal disease. Mandibular distoclusion (class II malocclusion), in which the mandibular arch occludes caudal to its normal position relative to the maxillary arch, can further contribute to lingual displacement of mandibular canine teeth. Traditionally, a flowable self-curing bisacrylic composite material has been used. The method described here uses a light cure acrylic denture base material utilizing multiple customized segments to construct the appliance to the desired shape and size necessary to achieve a functional incline plane.

Craniometric geographical variation in Hylaeamys megacephalus populations / Variação geográfica craniométrica em populações de Hylaeamys megacephalus

Hylaeamys megacephalus (G. Fisher, 1814) presents great genetic diversity and wide geographical distribution, and occurs in both the Amazon and Cerrado biomes. Because of its generalist aspect, this species tolerates different eating habits and habitats. It occurs in flooded and dry areas and is predominantly terrestrial, which allows greater gene flow between populations even over long distances. Studies that seek a better understanding of morphological variations resulting from differences imposed by the environment throughout this species' distribution are still lacking. This study aimed to analyze the differences between H. megacephalus populations based on craniometry, investigating whether the environment has an influence on morphology. We analyzed a total of 142 specimens from three scientific mammal collections: National Museum, "Universidade Federal do Rio de Janeiro" (MN-UFRJ); "Laboratório de Biologia e Parasitologia de Mamíferos Reservatórios Silvestres", "Instituto Oswaldo Cruz", "Fundação Oswaldo Cruz"(LBCE-Fiocruz); and "Laboratório de Biodiversidade", "Universidade Federal de Goiás", "Regional Jataí" (LZE-UFG), and took 20 craniometric measurements. Craniometry was explored using unweighted pair group method with arithmetic mean (UPGMA), canonical variate analysis, and principal component analysis (PCA). The results led us to conclude that there are three craniometric groups of H. megacephalus with a tendency to differentiate as a result of geographical influences.(AU)

Com grande diversidade genética e distribuição geográfica, Hylaeamys megacephalus (G. Fisher, 1814) ocorre tanto na Amazônia quanto no Cerrado. Visto seu aspecto generalista, esta espécie tolera diversos hábitos alimentares e habitats, ocorrendo em áreas inundadas ou não, sendo predominantemente terrestre, permitindo maior fluxo de genes entre as populações, mesmo em longas distâncias. Apresenta ampla distribuição, e carece de estudos que busquem um melhor entendimento sobre as variações morfológicas resultantes das diferenças impostas pelo meio ao longo de sua distribuição. O estudo teve como objetivo, analisar as diferenças entre as populações de H. megacephalus, com base na craniometria investigando se o ambiente interfere na morfologia. Analisamos um total de 142 espécimes oriundos de coleções científicas de mamíferos, do Museu Nacional, Universidade Federal do Rio de Janeiro (MN-UFRJ), Laboratório de Biologia e Parasitologia de Mamíferos Reservatórios Silvestres, Instituto Oswaldo Cruz, Fundação Oswaldo Cruz (LBCE-Fiocruz) e Laboratório de Biodiversidade, Universidade Federal de Goiás, Regional Jataí, nos quais foram tomadas 20 medidas craniométricas. A craniometria foi explorada nas análises estatísticas de agrupamento de pares não ponderados com médias aritméticas (UPGMA), variação canônica e análise dos Componentes Principais (PCA). Os resultados encontrados nos levaram a concluir a existência de três grupos craniométricos da espécie de H. megacephalus com tendência a se diferenciarem, por influências geográficas.(AU)

A study on morphology and morphometric parameters on skull of the Bardhoka autochthonous sheep breed in Kosovo.

In this study, we aim to investigate the skull of Bardhoka sheep, which is the native breed of Kosovo by utilising normal morphometric methods. Differences between male and female were also statistically analysed. Further, the parameters that can be used in gender discrimination were also analysed. The statistical analysis was based on a sample of 24 adult skulls of Bardhoka breed with 12 female and 12 male skulls. Altogether, 31 different measurements were taken morphologically and 7 different indices were applied. Except for the measurement's values of the orbit, measurement's values of length of the cheek tooth row and the measurement's values of height of the foramen magnum, all the measured values of males were higher than females. Nasal index, cranium index and skull index values were statistically significant between both genders. It is envisaged that the findings of this study will motivate and assist other comparative studies with other autochthonous sheep and goat breeds found in the Dukagjini region or in clinical veterinary practice and even in zooarchaeology.

Comparative skull anatomy of terrestrial and crevice-dwelling Trachylepis skinks (Squamata: Scincidae) with a survey of resources in scincid cranial osteology.

Skinks account for more than 25% of all lizard species; however, representatives of fewer than a quarter of all species have been characterized osteologically. All but a few of the available cranial descriptions concentrate solely on characters that can be seen externally on the intact skull. Mabuyid skinks of the genus Trachylepis are the dominant, fully limbed skinks in Sub-Saharan Africa, and nearly all species have the same generalized body plan. Although a few rock crevice-dwelling species possess slight body depression, extreme dorsoventral depression is observed only in Trachylepis laevis. We investigated the detailed skull anatomy of three Trachylepis skinks (T. laevis, T. sulcata, and T. gonwouoi, a recently described species allied to T. affinis) using high-resolution X-ray micro-computed tomography. Our goals were to review the scincid cranial osteology literature in a phylogenetic context, provide a detailed anatomical atlas for the mabuyid lineage, and investigate the morphological adaptations of the highly modified T. laevis. Our results demonstrate that there is significant morphological variation between these three taxa, including the loss and fusion of structures, as well as changes in the shape, scale, and relationship between individual elements. Trachylepis laevis possesses several osteological modifications that have produced a reducton in head depth that are likely functional consequences of extreme rupicolous habits, including a flat skull roof, many strongly recumbent elements, and a depressed neurocranium.We hypothesize these modifications may correspond to descreased bite force and increased capabilities of cranial kinesis. Our study is the first element-by-element description of a skink using computed tomography technology.

The Relationship between Brachycephalic Head Features in Modern Persian Cats and Dysmorphologies of the Skull and Internal Hydrocephalus.

BACKGROUND: Cat breeders observed a frequent occurrence of internal hydrocephalus in Persian cats with extreme brachycephalic head morphology. OBJECTIVE: To investigate a possible relationship among the grade of brachycephaly, ventricular dilatation, and skull dysmorphologies in Persian cats. ANIMALS: 92 Persian-, 10 Domestic shorthair cats. METHODS: The grade of brachycephaly was determined on skull models based on CT datasets. Cranial measurements were examined with regard to a possible correlation with relative ventricular volume, and cranial capacity. Persians with high (peke-face Persians) and lower grades of brachycephaly (doll-face Persians) were investigated for the presence of skull dysmorphologies. RESULTS: The mean cranial index of the peke-face Persians (0.97 ± 0.14) was significantly higher than the mean cranial index of doll-face Persians (0.66 ± 0.04; P < 0.001). Peke-face Persians had a lower relative nasal bone length (0.15 ± 0.04) compared to doll-face (0.29 ± 0.08; P < 0.001). The endocranial volume was significantly lower in doll-face than peke-face Persians (89.6 ± 1.27% versus 91.76 ± 2.07%; P < 0.001). The cranial index was significantly correlated with this variable (Spearman's r: 0.7; P < 0.0001). Mean ventricle: Brain ratio of the peke-face group (0.159 ± 0.14) was significantly higher compared to doll-face Persians (0.015 ± 0.01; P < 0.001). CONCLUSION AND CLINICAL RELEVANCE: High grades of brachycephaly are also associated with malformations of the calvarial and facial bones as well as dental malformations. As these dysmorphologies can affect animal welfare, the selection for extreme forms of brachycephaly in Persian cats should be reconsidered.

Anatomical and radiographic study of the white-eared opossum (Didelphis albiventris) skull / Estudo anatômico e radiográfico do crânio no gambá-de-orelha-branca (Didelphis albiventris)

This study was made to investigate the anatomical features of the white-eared opossum skull, by osteology and radiographic anatomy. For this, five animals were used without sexual distinction. The skull was examined by radiographic and macroscopic characteristics. The skulls were then subjected to maceration. The skull was described macroscopically according to standard views, i.e. dorsal and caudal, lateral, ventral, and midsagittal. The skull can be divided into facial (viscerocranium) and cranial (neurocranium) regions. The facial region was elongated and more developed than neurocranium. The supraorbital foramen was absent. The tympanic bulla is not well developed. The zygomatic arch was formed by zygomatic process of the temporal bone, zygomatic process of the maxilla, and temporal process of the zygomatic bone. There was no significant difference between bones found in this study when compared with those described for others mammals. These findings may contribute to the better understanding of the anatomy and biology of the white-eared opossum.(AU)

Este estudo objetivou investigar as características anatômicas do crânio do gambá-de-orelha-branca, através da anatomia óssea e radiográfica. Para tanto, cinco animais foram usados sem distinção sexual. O crânio foi estudado através de análises radiográficas e macroscópicas. Para esta última, os crânios foram macerados. O crânio foi descrito macroscopicamente de acordo com as vistas ou normas rotineiras, isto é, dorsal e caudal, lateral, ventral e sagital. O crânio pode ser dividido em regiões facial (viscerocrânio) e cranial (neurocrânio). A região facial se mostrou alongada e mais desenvolvida que o neurocrânio. O forame supraorbital estava ausente. A bula timpânica não era bem desenvolvida. O arco zigomático era formado pelo processo zigomático do osso temporal, processo zigomático da maxila, e pelo processo temporal do osso zigomático. Não houve diferenças significativas entre os ossos estudados quando comparados com os já descritos para outros mamíferos. Estes resultados podem contribuir com um melhor entendimento da anatomia e biologia deste animal.(AU)

Morphological Variations in the Transverse Venous Sinus Anatomy of Dogs and its Relationship to Skull Landmarks.

We characterized the anatomical morphology of the transverse venous sinus (TVS) of 69 canine adult cadavers belonging to three groups: brachycephalic (B), dolichocephalic (D) and mesaticephalic (M). In addition, we outlined its path over the skull using five classic human craniometric points (CPs): the asterion (ast), the bregma (b), the glabella (g), the stephanion (st) and the pterion (pt). The study aimed to establish anatomical differences in the TVS between groups and in the relationship between the TVS and skull. We found that TVS anatomy and its relationships to skull landmarks vary markedly between the groups, with similar anatomical arrangements in B and M. The TVS length can be ranked as M < B < D (with D being the biggest), whereas the width can be ranked as M < D < B (with B being the widest) with the right side being smaller than the left. In the B and M groups, the TVS assumes a craniocaudal trajectory that is closer to the lateral skull wall than in D, where the TVS presents a caudocranial direction. By documenting the morphological characteristics of the TVS, we can create a set of anatomical references allowing construction of a basic framework to greatly decrease the probability of TVS injury during neuronavigation procedures when supported by a good knowledge of the skull, brain anatomies and their relationships.

Measurement of Incisor Overjet and Physiological Diastemata Parameters in Quarter Horse Foals.

Cephalometric studies are important to quantify abnormalities of jaw length and positioning. In this study, 4 to 7-month-old Quarter horse foals (n = 51) were examined to determine overjet (horizontal overlap) prevalence and measure the size of the physiological diastemata. Results were analyzed in relation to age, sex, and lineage. Another aim of this study was to develop a simple field technique for measuring incisor malocclusion and physiological diastemata dimensions that could be used to monitor the growth of the rostral components of maxilla, incisive bone, and mandible. The overall prevalence of overjet lesions in these foals was 51%. Females were overrepresented (61.5%). Overjet occurred more commonly in show foals (50% prevalence) than other working (7.7%) and race (42.3%) lineage foals. Significant differences were found between maxillary and mandibular physiological diastemata lengths in foals of all ages and, as expected, there was a positive statistical correlation between age and maxillary and mandibular physiological diastemata measurements. Incisor overjet was present in 44.4% of 4-month-old foals, 45.5% of 5-month-old foals, 58.3% of 6-month-old foals, and 60% of 7-month-old foals. There was a weak positive correlation between age and the presence of incisor overjet. It was concluded that incisor overiet was common among Quarter horse foals, especially those from show and race lineages. The field technique for physiological diastema measurements was considered effective.

Estimation of mouse fetal weight by ultrasonography: application from clinic to laboratory.

Ultrasonographic assessment of fetal growth to estimate fetal weight has been widely used in clinical obstetrics but not in laboratory mice. Even though it is important to assess fetal growth abnormalities for gene-targeting studies using mice, there have been no reports of accurately estimated fetal weight using fetal biometric parameters in mice. The aim of this study was to establish an accurate mouse formula using fetal biometric parameters under ultrasound imaging. Using a high-frequency ultrasound system with a 40 MHz transducer, we measured 293 fetuses of biparietal diameter and mean abdominal diameter from day 12.5 postcoitus (p.c.) until day 18.5 p.c every day. Thirteen algorithms for humans based on head and/or abdominal measurements were assessed. We established an accurate formula based on measurement of the abdomen in Jcl:ICR mice to investigate gestational complications, such as intrauterine growth restriction.

Comparison of two approaches to performing an inferior alveolar nerve block in the horse.

OBJECTIVES: To compare two approaches to performing the inferior alveolar nerve block in the horse and to evaluate the consistency of described topographical landmarks. DESIGN: Experimental cadaver model. METHODS: Eleven cadaver heads were positioned to mimic a standing sedated horse and the position of the mandibular foramen approximated. The vertical approach to the approximate location of the mandibular foramen was undertaken and red dye was deposited. The angled approach was then undertaken and blue ink was used to identify it. The heads were then dissected to determine the location of the dye. Placement was categorised as a hit or a miss for each technique for each side of the head. The distance of the dye from the nerve was recorded. Straight lateral radiographs of the sectioned heads were taken to evaluate the topographical landmarks for performing this nerve block. RESULTS: Each method was performed 22 times. A hit was achieved 16 times (73%) for the angled approach and 13 times (59%) for the vertical approach. There was no significant difference between the two approaches (P = 0.34). Radiographs revealed that the topographical landmarks used to approximate the mandibular foramen were relatively accurate. CONCLUSION: Both methods were found to be equivalently accurate. The previously reported topographic landmarks for locating the approximate position of the mandibular foramen on the medial aspect of the mandible were found to be accurate, but currently recommended doses of local anaesthetic may be excessive.

Skull typology of Byzantine dogs from the Theodosius Harbour at Yenikapi, Istanbul.

This study presents the results of craniometric analysis of 500 Byzantine Era dog skulls from the ancient site of the Theodosius Harbour in Istanbul (modern Yenikapi neighbourhood). To determine the typology of the skulls, up to 36 craniometric measurements were taken on each specimen. Fourteen indices and ratios were calculated from the measurements. Results show that the majority (97%) of the Byzantine dogs from the Yenikapi excavations were of mesocephalic type. Only 15 of the analysed skulls (3%) were of the dolichocephalic type. Only one dog skeleton has been recovered in situ during the excavations; analysis indicates that this individual belonged to a mesocephalic type dog. Brachycephalic dog skulls were absent in the samples studied from Byzantine Yenikapi. The results give important insight in continuities and discontinuities in dog-breeding traditions from the Roman to the Byzantine Eras, and between the West and the East during Medieval times.

Examination of the depth of the equine hard palate.

Equine behavioral problems and loss of optimum performance have been associated with musculoskeletal injury and, more recently, dental disease. Injuries to a horse's tongue and bars of the mandible due to bitting have been documented. However, another point of contact of the bit, the hard palate, has thus far been virtually ignored. The objective of the study was to determine if there was a significant range associated with the depth of the equine hard palate and if this range was associated with a certain breed, age, or sex of the horse. Oral examinations were performed on 52 horses and a measurement of the hard palate was taken. The study group was comprised of 27 mares, 24 geldings and 1 stallion. They were further divided into the age groups: 3-5 years (3), > 5-10 years (18), > 10-15 years (19), and > 15 years (12). Lastly, the groups were divided into the following breed categories: Quarter Horse, Thoroughbred, and Other. Analyses revealed that palate depth has a broad range that is not associated with any breed, age, or sex. Normal reference ranges were established for the data and suggests that the hard palate should be considered and measured when choosing a bit. Further research is necessary to determine which bits are best suited for each palate depth.

Cephalometric measurements and determination of general skull type of Cavalier King Charles Spaniels.

The general skull morphology of the head of the Cavalier King Charles Spaniel (CKCS) was examined and compared with cephalometric indices of brachycephalic, mesaticephalic, and dolichocephalic heads. Measurements were taken from computed tomography images. Defined landmarks for linear measurements of were identified using three-dimensional (3D) models. The calculated parameters of the CKCS were different from all parameters of mesaticephalic dogs but were the same as parameters from brachycephalic dogs. However, the CKCS had a wider braincase in relation to length than in other brachycephalic breeds. Studies of the etiology of the chiari-like malformation in the CKCS should therefore focus on brachycephalic control groups. As Chari-like malformation has only been reported in brachycephalic breeds, its etiology could be associated with a higher grade of brachycephaly, meaning a shorter longitudinal extension of the skull. This has been suggested for other breeds.

Sex and the frontal cortex: A developmental CT study in the spotted hyena.

The purpose of this study was to examine developmental and individual variation in total endocranial volume and regional brain volumes, including the anterior cerebrum, posterior cerebrum and cerebellum/brain stem, in the spotted hyena (Crocuta crocuta). The spotted hyena is a highly gregarious animal noted for living in large, hierarchically organized groups. The social lives of male and female spotted hyenas do not differ until after puberty, when males disperse from the natal group, while females remain philopatric. Here we sought to determine whether the divergent life histories of male and female spotted hyenas are linked to differences in brain size or organization. Three-dimensional virtual endocasts were created using computed tomography from 46 spotted hyenas skulls (23 females, 22 males, 1 unknown sex) ranging in age from 1 day to 18 years. Brain volume and skull length were highly correlated (r = 0.91), and both reached asymptotic values by 34 months of age. Analyses of total endocranial volume (relative to skull length) and cerebellum/brain stem volume (relative to total endocranial volume) revealed no sex differences. However, relative anterior cerebrum volume, comprised mainly of frontal cortex, was significantly greater in adult males than adult females, and relative posterior cerebrum volume was greater in adult females than adult males. We hypothesize that the demands of neural processing underlying enhanced social cognition required for successful male transfer between matriarchical social groups at dispersal may be greater than cognitive demands on philopatric females.