Measurements of postnatal growth of the skull of Pan troglodytes verus using lateral cephalograms

The postnatal growth of the viscerocranium in relation to the neurocranium of Pan troglodytes verus has been investigated using standardized lateral cephalograms. Sex and age were determined on the basis of cranial morphology and the skulls were divided into four age groups: infantile, juvenile, subadult and adult. The cephalograms were traced on transparencies and specific anatomical landmarks were identified for the measurement of lines angles and the area of the neurocranium and viscerocranium. The results showed that the skull of Pan troglodytes verus exhibits klinorhynchy. During postnatal growth it develops towards airorhynchy, but never shows true airorhynchy. In the infantile age group the measured area of the neurocranium is larger than that of the viscerocranium. The measured area of the viscerocranium increases until adulthood and is larger than that of the neurocranium in the subadult and adult group. From the results we conclude that in Pan troglodytes verus growth of the neurocranium seizes early in juvenile individuals, whereas the viscerocranium grows until adulthood. This may reflect an adaptation to the masticatory system.     

Sexual dimorphism in the skull of the European mink<Emphasis Type="Italic">Mustela lutreola</Emphasis> from NW part of Russia

Morphometric variation in 22 characters of 86 skulls of the European minkMustela lutreola (Linnaeus, 1761), from the NW part of Russia, has been analysed. Stepwise discriminant analysis was used to estimate craniometric variables for sex determinations. Two characters (zygomatic breadth and interorbital width) are enough for the 96.5% correct classification. The male skull ofM. lutreola is characterised by a relatively high neurocranium, widely arranged zygomatic arches, a wide rostrum, and by wider auditory bullae and higher mandibles. Sexual size dimorphism ofM. lutreola is less than that of other similar-sized mustelids —Mustela putorius, M. eversmanii, M. sibirica, Neovison vison. The results are discussed in relation to the existing theories on sexual dimorphism in mustelids.     

Craniometric variation in Norwegian wolverines Gulo gulo L.

Craniometric variation in Norwegian wolverines was analysed using univariate and multivariate techniques. The wolverine skull seems to be full-grown after about 9 months in both sexes although some dimensions continued to grow at a slow rate after the first year. Size allometry was studied in skulls older than 11 months. Allometric coefficients were calculated from different methods. The multivariate allometric coefficients were found to reflect the same allometric patterns as were found from the reduced major axis and from the direction cosines of PCI, whereas the coefficients seem to be underestimated by the least-square regression method. Sexual dimorphism was found to be highly significant, males being the larger sex. The female skulls were found to be relatively broader and to have a relatively higher coronoid process than the male skulls. It seems that the females have a relatively stronger feeding apparatus than the males, which leads to less absolute differences in strength, as reflected in a very high degree of dietary overlap. Two discriminant functions were calculated which both classified the material into their correct sex with nearly 100% accuracy. Geographical variation between samples from Nordland and Finnmark counties were studied. No significant multivariate variation was found between the female skulls. The male variation was highly significant; the Nordland skulls seem to have longer carnassials than those from Finnmark.     

Craniometric variation in Norwegian wolverines Gulo gulo L.

Craniometric variation in Norwegian wolverines was analysed using univariate and multivariate techniques. The wolverine skull seems to be full-grown after about 9 months in both sexes although some dimensions continued to grow at a slow rate after the first year. Size allometry was studied in skulls older than 11 months. Allometric coefficients were calculated from different methods. The multivariate allometric coefficients were found to reflect the same allometric patterns as were found from the reduced major axis and from the direction cosines of PCI, whereas the coefficients seem to be underestimated by the least-square regression method. Sexual dimorphism was found to be highly significant, males being the larger sex. The female skulls were found to be relatively broader and to have a relatively higher coronoid process than the male skulls. It seems that the females have a relatively stronger feeding apparatus than the males, which leads to less absolute differences in strength, as reflected in a very high degree of dietary overlap. Two discriminant functions were calculated which both classified the material into their correct sex with nearly 100% accuracy. Geographical variation between samples from Nordland and Finnmark counties were studied. No significant multivariate variation was found between the female skulls. The male variation was highly significant; the Nordland skulls seem to have longer carnassials than those from Finnmark.     

Genetic influences on cranial form: variation among ranch and feral American mink Mustela vison (Mammalia: Mustelidae)

Multivariate statistical techniques were used to examine craniometric variation within and between ranch and feral populations of American mink (Mustela vison). An examination of variation between ranches revealed that differences are greater between ranches than within ranches, although all comparisons were statistically significant. There is highly significant variation within a population of mink sampled from a single ranch during a short time period; female mink of different pelt colour are differentiable by their skull shape but not by skull size. This offers evidence for a genetic background to cranial variation in ranch mink. Cranial sexual dimorphism is reduced in ranch mink, when compared to feral populations, and size accounts for a lesser proportion of the variation between the sexes in ranched populations. In addition, the skulls of ranched mink are larger, have a relatively shorter palate and a relatively narrower postorbital constriction compared to their feral counterparts. We believe this reduced dimorphism to be a product of relaxed sexual selection, lack of resource competition and selective breeding for larger specimens of both sexes within ranch populations.     

Intraspecific variation in the skull morphology of the black caiman Melanosuchus niger (Alligatoridae,Caimaninae)

Melanosuchus niger is a caimanine alligatorid widely distributed in the northern region of South America. This species has been the focus of several ecological, genetic and morphological studies. However, morphological studies have generally been limited to examination of interspecific variation among extant species of South American crocodylians. Here, we present the first study of intraspecific variation in the skull of M. niger using a two‐dimensional geometric morphometric approach. The crania of 52 sexed individuals varying in size were analysed to quantify shape variation and to assign observed shape changes to different types of intraspecific variation, that is, ontogenetic variation and sexual dimorphism. Most of the variation in this species is ontogenetic variation in snout length, skull depth, orbit size and the width of the postorbital region. These changes are correlated with bite force performance and probably dietary changes. However, a comparison with previous functional studies reveals that functional adaptations during ontogeny seem to be primarily restricted to the postrostral region, whereas rostral shape changes are more related to dietary shifts. Furthermore, the skulls of M. niger exhibit a sexual dimorphism, which is primarily size‐related. The presence of non‐size‐related sexual dimorphism has to be tested in future examinations.     

Maxillary changes and occlusal traits in crania with artificial fronto-occipital deformation

Artificial fronto-occipital deformation of the cranial vault was typical of pre-Columbian cultures in the central Andean coastal regions. We have studied the influence of this deformation on maxillary and mandibular morphology. Measurements were performed on 86 adult Ancon skulls with anteroposterior deformation. Undeformed skulls from the area of Makatampu (n = 52) were used as the control group. To explore the influence of the deformity on occlusion, the skulls were categorized using the Angle classification and the alignment of the interincisor midline. In the group of deformed skulls, there was an increase in lateral growth of the vault and of the base of the skull (P < 0.001), giving rise to a greater interpterygoid width of the maxilla (P < 0.001), and an increase in the transverse diameter of the palatal vault. The mandible presented an increase in the length of the rami (P < 0.001) and in the intercondylar width, with no alteration of mandibular length. The deformed skulls had normal (class I) occlusion, with no displacement of the midline. The difference in the asymmetry index between the two groups was not statistically significant. Artificial fronto-occipital deformation of the cranial vault provoked compensatory lateral expansion of the base that was correlated with the transverse development of the maxilla and mandible. Occlusion and sagittal intermaxillary position were not affected by the cranial deformity. These results provide evidence of the integration between the neurocranium and the viscerocranium in craniofacial development, and support the hypothesis of a compensatory effect of function.     

Variation in guenon skulls (I): species divergence, ecological and genetic differences

Guenons are the most diverse clade of African monkeys. They have varied ecologies, include arboreal and terrestrial species, and can be found in nearly every region of sub-Saharan Africa. Species boundaries are often uncertain, with a variable number of species and subspecies mostly recognised on the basis of their geographic distribution and pelage. If guenon soft tissue patterns show high variability, the same does not seem to hold for skull morphology. Guenon skulls are traditionally considered relatively undifferentiated and homogeneous. However, patterns of variation in skulls have never been examined using a large number of specimens sampled across the breadth of species diversity. Thus, in the present study, skulls of adult guenons and two outgroup species are analysed using three-dimensional geometric morphometrics. Three-dimensional coordinates of 86 anatomical landmarks were measured on 1,315 adult specimens belonging to all living guenon species except Cercopithecus dryas. Species are well-discriminated using shape but the best discrimination occurs when species have either a long evolutionary history (e.g., Allenopithecus nigroviridis) or represent extremes of size variation (Miopithecus sp. and Erythrocebus patas). Interspecific phenetic relationships reflect size differences. Four main clusters are found that mainly correspond to four size groups: the smallest species (Miopithecus sp.), the largest species (E. patas plus the study outgroups), a group of medium-small arboreal guenons, and a group of medium-large arboreal and terrestrial guenons. Correlations between interspecific shape distances and interspecific differences in size are higher than between shape distances and genetic distances. However, if only the component of interspecific shape variation which is not correlated to evolutionary allometry is used in the comparison with genetic distances, correlations are up to 1.4 times larger than those including allometric shape. The smallest correlations are those between shape and ecological distances, which is consistent with the lack of clusters clearly reflecting broad ecological specialisations (e.g., arboreality versus terrestriality). Thus, size, which is generally considered more evolutionarily labile than shape, seems to have played a major role in the evolution of the guenons. The incongruence between interspecific shape differences and phylogeny might be explained by a large proportion of shape changes having occurred along allometric trajectories that tend to be conserved within this clade.     

Cranial variation in British mustelids

Nineteen measurements were made on 136 skulls belonging to seven mustelid species: Meles meles (Eurasian badger), Mustela nivalis, (weasel), Mustela erminea (stoat), Mustela putorius (polecat), Lutra lutra (otter), Mustela furo (ferret), and Mustela vison (American mink), and polecat-ferret hybrids. To investigate shape, size-related effects were eliminated by dividing all measurements by their geometric means. Canonical variate analysis was used to reveal major interspecies distinctions. Excluding the ferrets and polecat-ferrets from the analysis, only 3.2% of the skulls misclassified (one mink, one weasel, and two stoats). Three groups separated on the first canonical axis: 1) badgers, 2) polecats, mink, and otters, and 3) stoats and weasels. The important variables were width of zygomatic arch and height of sagittal crest opposed to the postorbital distance, condylobasal length, and basilar length. Otters separated out on the second canonical axis; the most important variables were postorbital breadth and width of the postorbital constriction opposed to the basioccipital width. There was reasonable separation of polecats from mink on a combination of the second and third canonical axes. On the latter the most important variables were postorbital breadth opposed to postorbital distance. Addition of the ferret data showed that they lay closest to, and overlapped with, the polecats. The stoat and weasel data alone gave complete separation, with height of sagittal crest and width of zygomatic arch opposed to basioccipital width. However, using size-in data the best separation was the relationship between postorbital breadth and either basioccipital width or postorbital distance. Sexual dimorphism was demonstrated in the skulls of badgers but was shown to be relatively insignificant when compared to the interspecific differences.     

Facial heights: evolutionary relevance of postnatal ontogeny for facial orientation and skull morphology in humans and chimpanzees

Facial heights, i.e. the vertical distances between the superior and inferior limits of facial compartments, contribute to the orientation of the viscerocranium in the primate skull. In humans, vertical facial variation is among the main sources of diversity and frequently associated with an integrated suite of other cranio-mandibular traits. Facial heights and kyphosis are also important factors in interspecific variation and models of hominoid evolution. The ontogenetic determination of adult facial orientation and its relation to phylogenetic variation are unclear, but crucial in all previously mentioned respects. We addressed these issues in a sample of 175 humans and chimpanzees with Procrustes based geometric morphometrics, testing hypotheses of interspecific similarity in postnatal ontogenetic trajectories, early versus later ontogenetic facial pattern determination, and a developmental model of morphological integration. We analyzed the contribution of postnatal morphogenesis to adult vertical facial variation by partitioning morphological variation into a portion of pure growth allometry and a non-allometric fraction. A statistically significant difference of growth-allometries revealed that in both species growth established the adult skull proportions by vertical facial expansion, but while in chimpanzees the complete viscerocranium showed reorientation, in humans only the lower face was modified. In both species the results support a hypothesis of early facial pattern determination. A coincident emergence of morphological traits favors a hypothesis of developmental integration of the face, excluding traits of the basi- and neurocranium. Interspecific differences in integration may have implications for evolutionary studies. The present findings indicate that growth establishes the adult skull proportions and integrates principal facial orientation patterns, already there in early postnatal ontogeny.     

A quantitative approach to the cranial ontogeny of the puma

The cranial ontogeny of specialized mammals is relevant to the understanding of the connection of form and function in a developmental, ecological, and evolutionary context. As highly specialized carnivores, felids are of especial interest. We studied the postnatal ontogeny of the skull in Puma concolor (Mammalia: Carnivora: Felidae) using a quantitative approach. We interpreted our results in the light of a previous qualitative assessment of ontogenetic changes in the species. This represents one of the few integrative studies of skull development in any extant species of wild felids. We report patterns of multivariate allometry of 19 linear skull dimensions measured in 48 Argentine specimens. We examined the (jackknife resampled) departures from isometry as well as the interplay of isometric and allometric trends in shaping the puma skull. Both the qualitative and quantitative results indicate that the major ontogenetic changes are directly linked to cranial structures that support a developing masticatory apparatus and its associated jaw and neck musculature, which are essential for the action of canines and carnassials during the killing bite and slicing flesh. Sexual differences suggest allometric scaling (hypo- or hyper-morphosis) as key processes in the development of the puma skull.     

Developmental changes in the skull morphology of common minke whales Balaenoptera acutorostrata

We investigated growth‐related and sex‐related morphological changes in the skulls of 144 North Pacific common minke whales Balaenoptera acutorostrata. Measurement was conducted at 39 points on the skull and mandible to extract individual allometric equations relating the length and zygomatic width of the skull. The results revealed no significant differences in skull morphology by sex except for width of occipital bone. The size relative to the skull of the anatomical parts involved in feeding, such as the rostrum and mandible, increased after birth. In contrast, the sensory organs and the anatomical regions involved in neurological function, such as the orbit, tympanic bullae, and foramen magnum, were fully developed at birth, and their relative size reduced over the course of development. This is the first study to investigate developmental changes in the skull morphology using more than 100 baleen whale specimens, and we believe the results of this study will contribute greatly to multiple areas of baleen whale research, including taxonomy and paleontology. J. Morphol. 275:1113–1121, 2014. © 2014 Wiley Periodicals, Inc.     

Cranial evolution in sakis (Pithecia, Platyrrhini) I: interspecific differentiation and allometric patterns

Patterns of interspecific differentiation in saki monkey (Pithecia) skulls are quantitatively described. The taxonomic arrangement previously proposed by Hershkovitz ([1987] Am. J. Primatol. 12:387-468) is consistent with quantitative differences in saki morphology. Discriminant analyses on 39 skull traits show that Pithecia species and subspecies are well-differentiated. Morphological distances (D2) among sakis clearly show the morphological unity of the pithecia-chrysocephala (Pithecia) and irrorata-vanzolinii-monacha (Monacha) species groups. The Pithecia species group is distributed north of the Amazon and has a smaller cranium than the Monacha group, distributed south of that river. Despite the size difference, multivariate static allometric patterns among sakis are quite similar. After removing size and allometric changes in shape from the data, species and subspecies are still differentiated, although to a lesser extent. D2 distances obtained from these scale-corrected data are similar in magnitude and pattern to the original D2, but show a closer similarity of P. monacha with the Pithecia group. P. monacha is a scaled-up version of the smaller sakis.     

Ontogenetic shape changes in Pomacentridae (Teleostei,Perciformes) and their relationships with feeding strategies: a geometric morphometric approach

The present study explores the shape changes of cranial structures directly involved in food capturing during growth after reef settlement in two species of Pomacentridae (Dascyllus aruanus and Pomacentrus pavo). Landmark‐based geometric morphometrics were used to study allometric patterns and related shape changes in four skeletal units: neurocranium, suspensorium and opercle, mandible and premaxilla. At settlement, the larvae of both species have a relatively similar morphology, especially with respect to the mandible. Their shapes suggest a feeding mode defined as ram/suction‐feeding. Ontogenetic shape changes show a shift to a suction feeding mode of prey capture. The main transformations involved are an increase in height of the suspensorium and the opercle, an elevation of the supraoccipital crest, a relative shortening of the mandible, and a lengthening of the ascending process of the premaxilla. Shape changes of the mandible in the two studied species also reflect an increase of biting capacities. The high disparity between adult shape results from differences in the rate and in the length of ontogenetic trajectories, from divergence of the ontogenetic trajectories (neurocranium, mandible, and premaxilla) and parallel shifts of the trajectories in the size‐shape space (suspensorium and opercle). In an evolutionary context, allometric heterochronies during ontogeny of different skeletal unit of the head may be considered as a basis for the explanation of the diversity of damselfishes. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 92–105.     

Bone structure and the patterns of force transmission in the cat skull (Felis catus)

Projection microradiography was used to determine the density and orientation of the force transmitting structures, i.e., trabeculae and bone lying between approximately parallel vascular canals, within the bones of cat skulls. The organisation in the skulls was confirmed statistically for a total of ten cats. The results of the observations showed that within specific areas of the skull a high degree of structural orientation and an increased density of osseous structures was present. The distribution of these characters corresponded in contiguous bones such that a continuum of structural organisation was established between the alveolar region and the site of attachment of the temporalis and masseter muscles and the glenoid region. The patterns of force transmission during jaw closure were determined when a resistance was placed initially between the canines and then the carnassials. An analysis was first carried out on dry skulls using colophonium resin to determine the direction of the force distribution. The nature and the approximate magnitude of the forces were ascertained by replacing the resin with strain gauges. The basic similarities in the strain patterns recorded from the dry skulls and those from the ten anaesthetised cats in which strain gauges had been intra-vitally implanted, substantiated the recordings made on the dry skulls. Combination of the results from the three sets of experiments defined the patterns of force distribution in the cat skull during the closure of the mandible against a resistance. The results showed that: (1) the combined action of the temporalis and masseter muscles tended to reduce the overall strain in the skull bones, and that the deformations produced by the action of the masseter were greater than that exerted by the temporalis muscles; (2) during biting, whether the resistance was placed between the canines or carnassials, compressive forces predominated in the facial bones; (3) small movements observed between facial bones indicated the presence of a flexible component within the skull, thus allowing large forces to be exerted during biting without overstressing the facial bones; (4) the glenoid fossa is part of a force bearing joint; (5) forces generated during biting were resisted within the skull by forces of an opposite nature generated within the system, the incompressible nature of bone and by the effect of the soft tissues; (6) the nature and the magnitude of the strain altered when a resistance was placed at the canines and then at the carnassials; however, the pattern of force distribution within the skull remained the same; (7) there was a direct correspondence between the detailed structural organisation of the bones and the patterns of force distribution. This conclusion would appear to apply in general to mammalian skulls. The study also emphasises the importance, neglected hitherto, of carrying out a variety of experiments to determine the patterns of force distribution in bones. The Trajectorial Theory of bone organisation is discussed and, on the basis of the results obtained, a modified theory is proposed. This states that: the structural continuum is common to the compact and cancellous bone and comprises bony bars which are aligned in the optimum direction for the transmission of force to a region in the bone or bones where it is effectively resisted.     

Comparative allometric investigations on the skulls of wild cavies (Cavia aperea) versus domesticated guinea pigs (C. aperea f. porcellus) with comments on the domestication of this species

Bivariate allometric calculations were performed to quantitatively compare skulls of wild cavies with domesticated guinea pigs. Descendents of wild caught Cavia aperea from eastern regions of the species’ distribution area were used, as well as unselected domesticated breeds of guinea pigs differing in outer appearance. The individuals of both groups were kept under similar environmental conditions. Altogether 19 parameters on the skulls and the body weights were used for the analyses. These parameters were studied in relation to greatest skull length and to body size. As a general result the diverse parameters are in most cases significantly different between both groups which is interpreted as a special result of unconsciously selected and genetically determined intraspecific changes concomitant with domestication. The skull does not change in total under the domestication process but in a mosaic manner. However, for the mosaic changes of the diverse parameters in relation to skull length a different picture is valid as related to body weight. This is caused by the fact that the skull of guinea pigs is around 5% shorter independent of the body size, a common effect of domestication also described for other species. Thus, skull length is not an appropriate parameter for body size with respect to such intraspecific investigations, although normally used for the characterization of species in interspecific comparisons of museum materials.Altogether in relation to body weight most of the parameters describing the fascial portion of the skull are shorter in the guinea pig, especially the palatine, the diastema and the mandible but also the nasalia and frontalia lengths as well as the breadth of the rostrum and the zygomaticum are smaller. Most of the occipital skull measures are additionally smaller in the guinea pigs. This is clearly the case for the length and the breadth of the braincase and for the tympanic bulla. The braincase volume is 16.2% smaller, a value only slightly different when compared with the degree of brain size decrease due to domestication as reported for this species in other investigations.     

Morphometric study of allometric skull growth in the temnospondyl Archegosaurus decheni from the Permian/Carboniferous of Germany

The skulls of ninety-six specimens of the temnospondyl Archegosaurus decheni from the Permian/Carboniferous of Germany, ranging in length from almost 20 to almost 280 mm, are used in a morphometric analysis of cranial ontogeny. A Cartesian transformation, a bivariate regression analysis, and a principal component analysis (PCA) reveal changes of general skull proportions and of particular skull roofing bones during growth. The preorbital part of the skull exhibits a much faster growth rate than the postorbital region, whereas the orbits exhibit a considerable decrease in relative size. The skull bones possess low allometry coefficients of growth in width, what leads to a proportionally much more slender skull than in most other temnospondyls, comparable only to other archegosaurids, the cochleosaurid Chenoprosopus, and longirostrine stereospondyls like Australerpeton and trematosaurids. Distinctly negative allometry of the width of the cheek region, where part of the adductor musculature originated, suggests a weaker bite in A. decheni than in temnospondyls with broad-parabolic skulls like Onchiodon and Sclerocephalus. Results from the analysis of skull growth in A. decheni offer a biological interpretation of the life habits of this animal as becoming increasingly more adaptated to piscivory during ontogeny. The continuous growth of the skull with a gradual shift in proportions supports, in conjunction with morphological data, the hypothesis that A. decheni did not undergo a metamorphosis.     

Mandible shape in marsupial and placental carnivorous mammals: a morphological comparative study using geometric morphometrics

We analysed mandible shape of the orders Dasyuromorpha, Didelphimorphia, and Carnivora using two‐dimensional geometric morphometrics, in order to explore the relationship between shape, size, and phylogeny. We studied 541 specimens, covering most of the genera of the terrestrial Carnivora (115 species) and a wide sample of marsupials (36 species). The observed shape variation had an ecological component. As an example, omnivorous carnivores have thick mandibles and large talonids in the carnassials, while hypercarnivores possess short mandibles and reduced talonids. There is also a discrimination between different taxonomic groups (i.e. marsupials and Carnivora), indicating some kind of constraint. Size explains a large percentage of total variance (large species had shorter and stronger mandibles, with anteriorly displaced carnassials), was significant when phylogeny was taken into account with a comparative method, but not when size and shape were optimized on the phylogeny. Carnivora presents a larger disparity and variation in body size, which could be related to the difference in teeth replacement. The optimization of mandible shape on the phylogenetic tree indicates that functional aspects, such as diet, are a key factor in the evolution of the carnivore mandible, but also that there is a phylogenetic pattern that cannot be explained by differences in diet alone. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 164 , 836–855.     

Evolution of ontogenetic allometry shaping giant species: a case study from the damselfish genus Dascyllus (Pomacentridae)

The evolution of body size, the paired phenomena of giantism and dwarfism, has long been studied by biologists and paleontologists. However, detailed investigations devoted to the study of the evolution of ontogenetic patterns shaping giant species are scarce. The damselfishes of the genus Dascyllus appear as an excellent model for such a study. Their well understood phylogeny reveals that large‐bodied species have evolved in two different clades. Geometric morphometric methods were used to compare the ontogenetic trajectories of the neurocranium and the mandible in both small‐bodied (Dascyllus aruanus and Dascyllus carneus; maximum size: 50–65 mm standard length) and giant (Dascyllus trimaculatus and Dascyllus flavicaudus; maximum size: 90–110 mm standard length) Dascyllus species. At their respective maximum body size, the neurocranium of the giant species is significantly shorter and have a higher supraoccipital crest relative to the small‐bodied species, whereas mandible shape variation is more limited and is not related to the ‘giant’ trait. The hypothesis of ontogenetic scaling whereby the giant species evolved by extending the allometric trajectory of the small‐bodied ones (i.e. hypermorphosis) is rejected. Instead, the allometric trajectories vary among species by lateral transpositions. The rate of shape changes and the type of lateral transposition also differ according to the skeletal unit among Dascyllus species. Differences seen between the two giant species in the present study demonstrate that giant species may appear by varied alterations of the ancestor allometric pattern. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 99–117.     

The influence of feeding on the evolution of sensory signals: a comparative test of an evolutionary trade‐off between masticatory and sensory functions of skulls in southern African Horseshoe bats (Rhinolophidae)

The skulls of animals have to perform many functions. Optimization for one function may mean another function is less optimized, resulting in evolutionary trade‐offs. Here, we investigate whether a trade‐off exists between the masticatory and sensory functions of animal skulls using echolocating bats as model species. Several species of rhinolophid bats deviate from the allometric relationship between body size and echolocation frequency. Such deviation may be the result of selection for increased bite force, resulting in a decrease in snout length which could in turn lead to higher echolocation frequencies. If so, there should be a positive relationship between bite force and echolocation frequency. We investigated this relationship in several species of southern African rhinolophids using phylogenetically informed analyses of the allometry of their bite force and echolocation frequency and of the three‐dimensional shape of their skulls. As predicted, echolocation frequency was positively correlated with bite force, suggesting that its evolution is influenced by a trade‐off between the masticatory and sensory functions of the skull. In support of this, variation in skull shape was explained by both echolocation frequency (80%) and bite force (20%). Furthermore, it appears that selection has acted on the nasal capsules, which have a frequency‐specific impedance matching function during vocalization. There was a negative correlation between echolocation frequency and capsule volume across species. Optimization of the masticatory function of the skull may have been achieved through changes in the shape of the mandible and associated musculature, elements not considered in this study.