Search

Laryngeal echolocation in bats could have evolved following two scenarios: a single origin from a common ancestor or an independent acquisition inside the two clades Yinpterochiroptera and Yangochiroptera. Later, some members of Yinpterochiroptera possibly lost their ability to echolocate. In bats, the larynx produces vocalizations for communication and, in most species, for echolocation. Here, we describe how comparative chiropteran laryngeal morphology is a novel area of research that could improve the understanding of echolocation and may help resolve the evolutionary history of bats. This review provides morphological descriptions and comparisons of the bat larynx and bioacoustics interpretations. We discuss the importance of understanding: (1) laryngeal sound production so it may be linked with the evolution of the chiropteran auditory system; and (2) the evolution of laryngeal morphology to understand the ecological and behavioural aspects of bat biology. We find that a strong phylogenetic signal is potentially the main source explaining macroevolutionary variation in laryngeal form among bats. We predict that the three parameters of sound production in echolocation (frequency, intensity, and rate of calls) are independently modulated by different laryngeal components, but this hypothesis remains understudied in terms of species diversity.

The phylogenetic relationships of major groups within the Order Eulipotyphla was once highly disputed, but the advent of molecular studies has greatly improved our understanding about the diversification history of talpids, soricids, erinaceids, and solenodontids. Their resolved phylogenetic relationships now allow us to revisit the turbinal and lamina evolution of this group. The inner structure of the nasal cavity of mammals is highly complicated and the homologies of the turbinals among mammalian species are still largely unsettled. In this regard, investigation on fetal anatomy and ontogenetic changes of the nasal capsule allows us to evaluate the homologies of the turbinals and laminae. We observed various fetuses and adults of talpids and soricids using high-resolution diffusible iodine-based contrast-enhanced computed tomography (diceCT) and reviewed previous reports on erinaceids, solenodontids, and other laurasiatherians. Although the turbinal and lamina morphology was previsouly considered to be similar among eulipotyphlans, we found phylogenetic patterns for talpids and soricids. The nasoturbinal of the common ancestor of talpids and soricids was most likely rostrocaudally elongated. The epiturbinal at the ethmoturbinal II disappeared in soricids independently. Finally, we propose two possible scenarios for the maxilloturbinal development: 1) the maxilloturbinal of talpids and soricids became small independently with a limited number of lamellae as a result of convergent evolution, or 2) the common ancestor of talpids and soricids already had a small and simple maxilloturbinal.

This study integrates analyses of mitochondrial DNA sequences and morphological and acoustic data to re-evaluate the taxonomic status of Rhinolophus rex rex, R. r. paradoxolophus and R. schnitzleri throughout their distribution ranges. Based on a dense geographic sampling of specimens hitherto referred to these taxa and contrary to the current taxonomic view, our results indicate that all examined specimens of these taxa are representatives of a single, widely distributed and morphologically variable species, R. rex. The recognition of its geographic populations as different subspecies (R. r. rex and R. r. paradoxolophus) or distinct species (R. schnitzleri) based on morphological and acoustic data should be regarded as invalid. In the light of this revision, we also reassess the conservation status of R. rex against IUCN Red List criteria as Near Threatened.

Syndromic craniosynostosis (CS) patients exhibit early, bony fusion of calvarial sutures and cranial synchondroses, resulting in craniofacial dysmorphology. In this study, we chronologically evaluated skull morphology change after abnormal fusion of the sutures and synchondroses in mouse models of syndromic CS for further understanding of the disease. We found fusion of the inter-sphenoid synchondrosis (ISS) in Apert syndrome model mice (Fgfr2

The anatomical framework of the jawbones is highly conserved among most of the Osteichthyes, including the tetrapods. However, our recent study suggested that the premaxilla, the rostralmost upper jaw bone, was rearranged during the evolution of therian mammals, being replaced by the septomaxilla at least in the lateral part. In the present study, to understand more about the process of evolution from the ancestral upper jaw to the therian face, we re-examined the development of the therian premaxilla (incisive bone). By comparing mouse, bat, goat, and cattle fetuses, we confirmed that the therian premaxilla has dual developmental origins, the lateral body and the palatine process. This dual development is widely conserved among the therian mammals. Cell-lineage-tracing experiments using Dlx1-CreER

Bats show a remarkable ecological diversity that is reflected both in dietary and foraging guilds (FGs). Cranial ecomorphological adaptations linked to diet have been widely studied in bats, using a variety of anatomical, computational and mathematical approaches. However, foraging-related ecomorphological adaptations and the concordance between cranial and postcranial morphological adaptations remain unexamined in bats and limited to the interpretation of traditional aerodynamic properties of the wing (e.g. wing loading [WL] and aspect ratio [AR]). For this reason, the postcranial ecomorphological diversity in bats and its drivers remain understudied. Using 3D virtual modelling and geometric morphometrics (GMM), we explored the phylogenetic, ecological and biological drivers of humeral morphology in bats, evaluating the presence and magnitude of modularity and integration. To explore decoupled patterns of variation across the bone, we analysed whole-bone shape, diaphyseal and epiphyseal shape. We also tested whether traditional aerodynamic wing traits correlate with humeral shape. By studying 37 species from 20 families (covering all FGs and 85% of dietary guilds), we found similar patterns of variation in whole-bone and diaphyseal shape and unique variation patterns in epiphyseal shape. Phylogeny, diet and FG significantly correlated with shape variation at all levels, whereas size only had a significant effect on epiphyseal morphology. We found a significant phylogenetic signal in all levels of humeral shape. Epiphyseal shape significantly correlated with wing AR. Statistical support for a diaphyseal-epiphyseal modular partition of the humerus suggests a functional partition of shape variability. Our study is the first to show within-structure modular morphological variation in the appendicular skeleton of any living tetrapod. Our results suggest that diaphyseal shape correlates more with phylogeny, whereas epiphyseal shape correlates with diet and FG.

Anatomy of bat genital organs has been conventionally studied by gross and microscopic observations to date. Here, we employ both histological observation and diceCT (diffusible iodine-based contrast-enhanced computed tomography) to study the detailed three-dimensional morphological structure of the male genital organs in bats, using the greater horseshoe bat, Rhinolophus ferrumequinum. This is the first study to three-dimensionally describe the whole reproductive organs of bats in detail. Our highly resolved three-dimensional reconstruction reveals that the male organs of R. ferrumequinum consist of paired testes, epididymides, deferent ducts, and five accessory genital glands. The boundary between the ampullary and vesicular glands has been difficult to identify in previous observations, but our diceCT imaging allowed us to clearly differentiate the two. We found that the ampullary gland is located at the terminal part of the deferent ducts, and the vesicular gland lies distal to the ampullary glands. This species possesses a single and carrot-shaped urethral gland, which is not found in most chiropteran families. The presence of the urethral gland in this species and its secretions suggest that after copulation this species is capable of forming a vaginal plug, which can seal the female’s vaginal orifice to block the entrance of spermatozoa from other males. The presence of the urethral gland and elongated epididymal tail and the fact that some individuals can terminate their hibernation and reactivate imply forced copulation on hibernating females can occur in R. ferrumequinum.

Haeckel's recapitulation theory has been a controversial topic in evolutionary biology. However, we have seen some recent cases applying Haeckel's view to interpret the interspecific variation of prenatal ontogeny. To revisit the validity of Haeckel's recapitulation theory, we take bats that have undergone drastic morphological changes and possess a characteristic ecology as a case study. All members of Rhinolophoidea and Yangochiroptera can generate an ultrasonic pulse from the larynx to interpret surrounding objects (laryngeal echolocation) whereas Pteropodidae lacks such ability. It is known that the petrosal bone is particularly derived in shape and expanded in laryngeal echolocators. If Haeckel's recapitulation theory holds, the formation of this derived trait should occur later than those of other bones. Therefore, we compared the prenatal ossification timing of the petrosal in 15 bat species and five outgroup species. We found that the ossification of the petrosal is accelerated in laryngeal echolocators while it is the last bone to ossify in non-laryngeal echolocating bats and non-volant mammals, which runs counter to the prediction generated by Haeckel's recapitulation theory. We point out the evolutionarily labile nature of trait developmental timing and emphasize that Haeckel's recapitulation theory does not hold in many cases. We caution that generating predictions on ancestral conditions and evolutionary history leading from Haeckel's recapitulation theory is not well supported.

Bats use their forelimbs in different ways, but flight is the most notable example of morphological adaptation. Foraging and roosting specializations beyond flight have also been described in several bat lineages. Understanding postcranial evolution during the locomotory and foraging diversification of bats is fundamental to understanding bat evolution. We investigated whether different foraging and roosting behaviors influenced humeral cross-sectional shape and biomechanical variation, following Wolff's law of bone remodeling. The effect of body size and phylogenetic relatedness was also tested, in order to evaluate multiple sources of variation. Our results suggest strong ecological signal and no phylogenetic structuring in shape and biomechanical variation in humeral phenotypes. Decoupled modes of scaling of shape and biomechanical variation were consistently indicated across foraging and roosting behaviors, suggesting divergent allometric trajectories. Terrestrial locomoting and upstand roosting species showed unique patterns of shape and biomechanical variation across all our analyses, suggesting that these rare behaviors among bats place unique functional demands on the humerus, canalizing phenotypes. Our results suggest that complex and multiple adaptive pathways interplay in the postcranium, leading to the decoupling of different features and regions of skeletal elements optimized for different functional demands. Moreover, our results shed further light on the phenotypical diversification of the wing in bats and how adaptations besides flight could have shaped the evolution of the bat postcranium.

International audience; Yellow house bats (Scotophilus) have been known for centuries as a widespread genus of vesper bats in the Indomalayan Region. Despite this, their taxonomic status and phylogeographical patterns remain unclear due to differing criteria employed by early taxonomists and inconsistencies between morphological and molecular assessments. To address these issues, we undertook a comparative phylogeographic analysis of Asian Scotophilus spp. using integrated genetic and morphological analyses of samples collected across the region. These demonstrate that yellow house bats in Asia can be classified into just two widespread species, namely the smaller S. kuhlii (e.g., FA ≤ 53.1 mm, GLS ≤ 20.18 mm) and the larger S. heathii (e.g., FA ≥ 53.4 mm, GLS ≥ 20.85 mm), which occur in sympatry in different parts of the Indomalayan Region. Although these two sympatric species share similar eco‐ethological preferences, they differ considerably in their geographic distributions and intraspecific variation in mtDNA sequences and morphological traits. These disparities were likely misinterpreted as indicating potential cryptic diversity in previous studies, whereas we suggest they are related to interspecific differences in sex‐biased gene flow and phenotypic plasticity to adapt to varying environments. Our study highlights the importance of using multiple datasets to resolve taxonomic uncertainties and reconstruct demographic and phylogeographic histories of sympatric species.

Leaf-eating monkeys (colobines) are a highly diversified subfamily with 61 species in ten genera, in which patterns and constraints of morphological evolution are still poorly resolved. In the present study, we measured the skulls of 452 specimens collected from different museums worldwide. Using one of the most extensive samples ever employed, and geometric morphometric techniques, we aimed to elucidate the evolutionary processes that have led to the craniofacial diversification of colobines. Our comprehensive analyses of the colobine cranium demonstrated that phylogeny is the first order signal to emerge, with clear interspecific patterns of differentiation. Allometric trend constrains shape variation for most colobine taxa, but to a lesser degree than phylogeny. We also confirmed that diet is significantly associated with the variation in cranial shape among colobines. In particular, the mechanical advantage of the masseter for biting at the anterior dentition is linked to seed intake. We postulate that such ecomorphological patterns explain, in part, the non-phylogenetic and non-allometric variations in the colobine skull, and indicate the importance of diet in interspecific resource partitioning, allowing for species coexistence.

Interspecific diversity exists in cranial suture closure patterns among mammalian species. Suture closure patterns partly reflect phylogenesis, but it has also been claimed that it is influenced by biomechanical factors. Here we provide the first report on the cranial suture closure pattern in water deer. Among cervids, the water deer is an exceptional species, as it is the only one without antlers. Instead, the male water deer possess prominent canines, which are utilized during male-male combats. This unique morphological setting allowed us to examine whether the presence of prominent canines affects cranial suture closure. We found that the only sexual difference in cranial suture closure pattern is the closure of the interfrontal suture in males, which is found in some other cervid species as well. Except for the interfrontal suture closure, timing and sequence of cranial suture closure were comparable between both sexes, suggesting that the presence of prominent canines in males has no influence on cranial suture closure pattern. Our results indicate that interfrontal suture closure in males is a phylogenetic pattern, i.e. an apomorphy for Capreolini, Hydropotini and Alceini.

Background Self-powered flight is one of the most energy-intensive types of locomotion found in vertebrates. It is also associated with a range of extreme morpho-physiological adaptations that evolved independently in three different vertebrate groups. Considering that development acts as a bridge between the genotype and phenotype on which selection acts, studying the ossification of the postcranium can potentially illuminate our understanding of bat flight evolution. However, the ontogenetic basis of vertebrate flight remains largely understudied. Advances in quantitative analysis of sequence heterochrony and morphogenetic growth have created novel approaches to study the developmental basis of diversification and the evolvability of skeletal morphogenesis. Assessing the presence of ontogenetic disparity, integration and modularity from an evolutionary approach allows assessing whether flight may have resulted in evolutionary differences in the magnitude and mode of development in bats. Results We quantitatively compared the prenatal ossification of the postcranium (24 bones) between bats (14 species), non-volant mammals (11 species) and birds (14 species), combining for the first time prenatal sequence heterochrony and developmental growth data. Sequence heterochrony was found across groups, showing that bat postcranial development shares patterns found in other flying vertebrates but also those in non-volant mammals. In bats, modularity was found as an axial-appendicular partition, resembling a mammalian pattern of developmental modularity and suggesting flight did not repattern prenatal postcranial covariance in bats. Conclusions Combining prenatal data from 14 bat species, this study represents the most comprehensive quantitative analysis of chiropteran ossification to date. Heterochrony between the wing and leg in bats could reflect functional needs of the newborn, rather than ecological aspects of the adult. Bats share similarities with birds in the development of structures involved in flight (i.e. handwing and sternum), suggesting that flight altriciality and early ossification of pedal phalanges and sternum are common across flying vertebrates. These results indicate that the developmental modularity found in bats facilitates intramodular phenotypic diversification of the skeleton. Integration and disparity increased across developmental time in bats. We also found a delay in the ossification of highly adaptable and evolvable regions (e.g. handwing and sternum) that are directly associated with flight performance. Electronic supplementary material The online version of this article (10.1186/s12862-019-1396-1) contains supplementary material, which is available to authorized users.

Mammals feature not only great phenotypic disparity, but also diverse growth and life history patterns, especially in maturity level at birth, ranging from altriciality to precocity. Gestation length, morphology at birth, and other markers of life history are fundamental to our understanding of mammalian evolution. Based on the first synthesis of embryological data and the study of new ontogenetic series, we reconstructed estimates of the ancestral chronology of organogenesis and life-history modes in placental mammals. We found that the ancestor of marsupial and placental mammals was placental-like at birth but had a long, marsupial-like infancy. We hypothesize that mammalian viviparity might have evolved in association with the extension of growth after birth, enabled through lactation, and that mammalian altriciality is inherited from the earliest amniotes. The precocial lifestyle of extant sauropsids and that of many placental mammals were acquired secondarily. We base our conclusions on the best estimates and provide a comprehensive discussion on the methods used and the limitations of our dataset. We provide the most comprehensive embryological dataset ever published, "rescue" old literature sources, and apply available methods and illustrate thus an approach on how to investigate comparatively organogenesis in macroevolution.

Most morphological and physiological adaptations associated with bat flight are concentrated in the postcranium, reflecting strong functional demands for flight performance. Despite an association between locomotory diversity and trophic differentiation, postcranial morphological diversity in bats remains largely unexplored. Evolutionary developmental biology is a novel approach providing a link between the analysis of genotypic and phenotypic variation resulting from selective pressures. To quantify the morphological diversity of the postcranium in bats and to explore its developmental basis, we reconstructed the postcranial allometric trajectories of nine bat species from different prenatal developmental series, representing five families and both suborders. We tested for allometric growth in Chiroptera and also quantified levels of allometric disparity and inter-trajectory distances. Using a phylogenetic scaffold, we assessed whether ontogenetic differences reflect evolutionary relationships. We found significant allometric growth trajectories in almost all species. Interspecific trajectory distances showed lower variance within Yinpterochiroptera than within Yangochiroptera and between suborders. Each suborder occupied nonoverlapping sections of allometric space, showing changes in the growth rates of specific bones for each suborder. The allometry-corrected disparity was significantly higher in larger species. Statistically significant phylogenetic signal in our results suggests that there is an ontogenetic basis for the postcranial morphological diversity in modern bats. Ancestral state reconstruction also showed an increase in the amount of change in shape with size in the larger species studied. We hypothesize that differences in allometric patterns among bat taxa may reflect a size-dependent evolutionary constraint, whereby variability in body size and allometric patterns are associated.

The recently increased interest in studies on sequence heterochrony has uncovered developmental variation betweenspecies. However,howchanges indevelopmental programarerelated to shiftsin life-history parameters remains largely unsolved. Here we provide the most comprehensive data to date on postcranial ossification sequence of bats and compare them to various boreoeutherian mammals withdifferentlocomotive modes. Giventhat batsareequippedwithanelongatedmanus, we expected to detect characteristic heterochronies particularly related to wing development. Although heterochronies related to wing development were confirmed as predicted, unexpected heterochronies regarding the pedal digits were also found. The timing of ossification onset of pedal phalanges is earlier than other mammals. Particularly, bats deviate from others in that pedal phalanges initiate ossification earlier than manual phalanges. It is known that the foot size of new born bats is close to that of adults, and that it takes several weeks to month until the wing is developed for flight. Giventhat thefoot is required tobe firm andstable enough atthetime ofbirth to allow continued attachment to the mother and/or cave walls, we suggest that the accelerated development of the hind foot is linked to their unique life history. Since the forelimb is not mature enough for flight at birth and requires extended postnatal time to be large enough to be fully functional, we postulate that bats invest in earlier development of the hindlimb. We conclud that energy allocation trade-offs can play a significant role in shaping the evolution of development. J. Exp. Zool. (Mol. Dev. Evol.) 9999B: XX-XX, 2014. © 2014 Wiley Periodicals, Inc. How to cite this article: Koyabu D, Son NT. 2014. Patterns of postcranial ossification and sequence heterochrony in bats: Life histories and developmental trade-offs. J. Exp. Zool. (Mol. Dev. Evol.) 9999:1-12.

Background Here we provide the most comprehensive study to date on the cranial ossification sequence in Lipotyphla, the group which includes shrews, moles and hedgehogs. This unique group, which encapsulates diverse ecological modes, such as terrestrial, subterranean, and aquatic lifestyles, is used to examine the evolutionary lability of cranial osteogenesis and to investigate the modularity of development. Results An acceleration of developmental timing of the vomeronasal complex has occurred in the common ancestor of moles. However, ossification of the nasal bone has shifted late in the more terrestrial shrew mole. Among the lipotyphlans, sequence heterochrony shows no significant association with modules derived from developmental origins (that is, neural crest cells vs. mesoderm derived parts) or with those derived from ossification modes (that is, dermal vs. endochondral ossification). Conclusions The drastic acceleration of vomeronasal development in moles is most likely coupled with the increased importance of the rostrum for digging and its use as a specialized tactile surface, both fossorial adaptations. The late development of the nasal in shrew moles, a condition also displayed by hedgehogs and shrews, is suggested to be the result of an ecological reversal to terrestrial lifestyle and reduced functional importance of the rostrum. As an overall pattern in lipotyphlans, our results reject the hypothesis that ossification sequence heterochrony occurs in modular fashion when considering the developmental patterns of the skull. We suggest that shifts in the cranial ossification sequence are not evolutionarily constrained by developmental origins or mode of ossification.

This study explores the relationship between feeding habit and craniodental morphology in two closely related sympatric callosciurine squirrels in south-east Asia: Callosciurus erythraeus and Dremomys rufigenis. Both C. erythraeus and D. rufigenis prefer fruits and insects, as generally seen in other tree squirrels. However, C. erythraeus also feeds extensively on hard seeds and tough tree bark, which are rarely included in the diet of D. rufigenis. We tested the hypothesis that C. erythraeus shows structural features in craniodental morphology that provide an advantage for feeding on hard seeds and tough tree bark. Results show that C. erythraeus possesses a greater mechanical advantage of the masseter and temporalis muscles for chewing, and a more robust zygomatic arch, compared with D. rufigenis. Callosciurus erythraeus is capable of generating a greater bite force at a given muscle force at the cheek teeth and its zygomatic arch is more resistant against the stresses generated by the masseter muscle, suggesting adaptation for feeding on hard seeds. Callosciurus erythraeus also exhibits greater leverage of the masseter and temporalis for incision and has a wider skull at the interorbital region, suggesting the capability for efficiently generating a greater bite force and a greater mechanical resistance to increased loads when biting into wood with its anterior dentition. Our findings indicate that the craniodental divergence between C. erythraeus and D. rufigenis may be linked functionally to the differences in their diets. We suggest that their morphological divergence may correlate with their dietary differences and contribute to the sympatric distribution of these closely related squirrels.

Stump-tailed macaques (Macaca arctoides) exhibit significant intraspecific variation in pelage color. Based on their pelage color and geographical distribution, they are classified into 2 subspecies: northern bright brown Macaca arctoides arctoides and southern black Macaca arctoides melanota. However, studies on the natural population are extremely scarce, and researchers have occasionally questioned the subspecific classification. We quantitatively examined pelage color variation of Macaca arctoides in 3 free-ranging populations in Thailand. Pelage color difference between populations is significant. The population distributed south of the Isthmus of Kra showed wide intrapopulational variation, including bright brown, dark brown, and completely black, whereas the northern populations primarily had dark brown hairs. Thus, we conclude that one cannot classify the color variants into subspecies. Further, we hypothesize that the distinctive polymorphism in southern Thailand resulted from geographical isolation caused by the Pleistocene eustatic fluctuations and subsequent recovery of land connection and subsequent gene flow.

Mammals display a broad spectrum of limb specializations coupled with different locomotor strategies and habitat occupation. This anatomical diversity reflects different patterns of development and growth, including the timing of epiphyseal growth plate closure in the long bones of the skeleton. We investigated the sequence of union in 15 growth plates in the limbs of about 400 specimens, representing 58 mammalian species: 34 placentals, 23 marsupials and one monotreme. We found a common general pattern of growth plate closure sequence, but one that is universal neither between species nor in higher-order taxa. Locomotor habitat has no detectable correlation with the growth plate closure sequence, but observed patterns indicate that growth plate closure sequence is determined more strongly through phylogenetic factors. For example, the girdle elements (acetabulum and coracoid process) always ossify first in marsupials, whereas the distal humerus is fused before the girdle elements in some placentals. We also found that heterochronic shifts (changes in timing) in the growth plate closure sequence of marsupials occur with a higher rate than in placentals. This presents a contrast with the more limited variation in timing and morphospace occupation typical for marsupial development. Moreover, unlike placentals, marsupials maintain many epiphyses separated throughout life. However, as complete union of all epiphyseal growth plates is recorded in monotremes, the marsupial condition might represent the derived state.

Background Talpids include forms with different degree of fossoriality, with major specializations in the humerus in the case of the fully fossorial moles. We studied the humeral microanatomy of eleven extant and eight extinct talpid taxa of different lifestyles and of two non-fossorial outgroups and examined the effects of size and phylogeny. We tested the hypothesis that bone microanatomy is different in highly derived humeri of fossorial taxa than in terrestrial and semi-aquatic ones, likely due to special mechanical strains to which they are exposed to during digging. This study is the first comprehensive examination of histological parameters in an ecologically diverse and small-sized mammalian clade. Results No pattern of global bone compactness was found in the humeri of talpids that could be related to biomechanical specialization, phylogeny or size. The transition zone from the medullary cavity to the cortical compacta was larger and the ellipse ratio smaller in fossorial talpids than in non-fossorial talpids. No differences were detected between the two distantly related fossorial clades, Talpini and Scalopini. Conclusions At this small size, the overall morphology of the humerus plays a predominant role in absorbing the load, and microanatomical features such as an increase in bone compactness are less important, perhaps due to insufficient gravitational effects. The ellipse ratio of bone compactness shows relatively high intraspecific variation, and therefore predictions from this ratio based on single specimens are invalid.

African colobine monkeys show considerable craniofacial variation among species, although the evolutionary causes of this diversity are unclear. In light of growing evidence that diet varies considerably among colobine species, we investigated whether colobine craniofacial morphology varies as a function of their diet. We compared craniofacial morphology among five African species: Colobus angolensis, C. guereza, C. polykomos, Piliocolobus badius, and P. verus. Matrix correlation analysis indicated a significant correlation between species-specific morphological distance and dietary distance matrices. The mechanical advantage of the masseter muscle was higher in seed-eaters (C. angolensis and C. polykomos) and lower in those that eat mainly young leaves (C. guereza, P. badius, and P. verus). Canonical correspondence analysis revealed that the durophagous colobines possess relatively wider bigonial breadths, anteroposteriorly shorter faces, shorter postcanine tooth rows, more medially positioned dental batteries, wider bizygomatic arches, and anteroposteriorly longer zygomatic arches. Under the constrained lever model, these morphological features suggest that durophagous colobines have the capacity to generate relatively greater maximum bite forces. However, no consistent relationship was observed between diet and variation in the mandibular corpus and symphysis, implying that robust mandibles are not necessarily adaptations for stress resistance. Factors that may influence mandibular robusticity include allometry of symphyseal curvature and canine tooth support. Finally, linear measures of mandibular robusticity may suffer from error.