Gape and bite force in the rodents Onychomys leucogaster and Peromyscus maniculatus: Does jaw‐muscle anatomy predict performance?

Compared with the deer mouse, Peromyscus maniculatus, the grasshopper mouse, Onychomys leucogaster, exhibits modifications in its jaw‐muscle architecture that promote wide gapes and large bite forces at wide gapes to prey upon large vertebrate prey. In this study, we determine whether jaw‐muscle anatomy predicts gape and biting performance in O. leucogaster, and we also assess the influence of gape on bite force in the two species. Although O. leucogaster has an absolutely longer jaw, which facilitates larger gapes, maximum passive gape is similar in both species, averaging ～12.5 mm. Thus, when scaled to jaw length, O. leucogaster has a smaller maximum passive gape. These results suggest that predatory behaviors of O. leucogaster may not require remarkably large gapes. On the other hand, both absolute and relative bite forces exerted by O. leucogaster are significantly larger than those of P. maniculatus. The largest bite forces in both species occur at 5.0 mm of gape at the incisors, or 40% of maximum gape. Although bite force in both species decreases at larger gapes, O. leucogaster does maintain a larger percentage of maximum bite force at gapes larger than 40% of maximum passive gape. Therefore, although structural modifications in the masticatory apparatus of O. leucogaster may constrain gape, they may help to maintain bite force at large gapes. These results suggest that increases in gape differentially influence the length‐tension properties of the jaw muscles in the two species. Finally, these results highlight the importance of considering the effect of muscle stretch on force production in comparative studies of bite force. As a first approximation, it appears that gapes of 40–50% of maximum gape in rodents optimizes bite force production at the incisors. J. Morphol., 2009. © 2009 Wiley‐Liss, Inc.     

Femoral neck structure and function in early hominins

All early (Pliocene–Early Pleistocene) hominins exhibit some differences in proximal femoral morphology from modern humans, including a long femoral neck and a low neck‐shaft angle. In addition, australopiths (Au. afarensis, Au. africanus, Au. boisei, Paranthropus boisei), but not early Homo, have an “anteroposteriorly compressed” femoral neck and a small femoral head relative to femoral shaft breadth. Superoinferior asymmetry of cortical bone in the femoral neck has been claimed to be human‐like in australopiths. In this study, we measured superior and inferior cortical thicknesses at the middle and base of the femoral neck using computed tomography in six Au. africanus and two P. robustus specimens. Cortical asymmetry in the fossils is closer overall to that of modern humans than to apes, although many values are intermediate between humans and apes, or even more ape‐like in the midneck. Comparisons of external femoral neck and head dimensions were carried out for a more comprehensive sample of South and East African australopiths (n = 17) and two early Homo specimens. These show that compared with modern humans, femoral neck superoinferior, but not anteroposterior breadth, is larger relative to femoral head breadth in australopiths, but not in early Homo. Both internal and external characteristics of the australopith femoral neck indicate adaptation to relatively increased superoinferior bending loads, compared with both modern humans and early Homo. These observations, and a relatively small femoral head, are consistent with a slightly altered gait pattern in australopiths, involving more lateral deviation of the body center of mass over the stance limb. Am J Phys Anthropol, 2013. © 2013 Wiley Periodicals, Inc.     

Food material properties and mandibular load resistance abilities in large-bodied hominoids

Numerous comparative studies have sought to demonstrate a functional link between feeding behavior, diet, and mandibular form in primates. In lieu of data on the material properties of foods ingested and masticated, many investigators have relied on qualitative dietary classifications such as "folivore" or "frugivore." Here we provide the first analysis of the relationship between jaw form, dietary profiles, and food material properties in large-bodied hominoids. We employed ratios of area moments of inertia and condylar area to estimate moments imposed on the mandible in order to evaluate and compare the relative ability to counter mandibular loads among central Bornean orangutans (Pongo pygmaeus wurmbii), Virunga mountain gorillas (Gorilla beringei beringei), and east African chimpanzees (Pan troglodytes schweinfurthii). We used data on elastic modulus (E) of fruit, fracture toughness (R) of fruit, leaves, and non-fruit, non-leaf vegetation, and derived fragmentation indices ( radicalR/E and radicalER), as proxies for bite force. We generated bending and twisting moments (forcexmoment arm) for various mandibular loading behaviors using food material properties to estimate minimally required bite forces. Based on E and R of foods ingested and masticated, we hypothesized improved resistance to mandibular loads in Pongo p. wurmbii compared to the African apes, and in G. b. beringei compared to Pan t. schweinfurthii. Results reveal that our predictions are borne out only when bite forces are estimated from maximum R of non-fruit, non-leaf vegetation. For all other tissues and material properties results were contrary to our predictions. Importantly, as food material properties change, the moments imposed on the mandible change; this, in turn, alters the entire ratio of relative load resistance to moment. The net effect is that species appear over- or under-designed for the moments imposed on the mandible. Our hypothesis, therefore, is supported only if we accept that maximum R of these vegetative tissues represents the relevant mechanical property influencing the magnitude of neuromuscular activity, food fragmentation, and mandibular morphology. A general implication is that reliable estimates of average and maximum bite forces from food material properties require that the full range of tissues masticated be tested. Synthesizing data on ingestive and masticatory behaviors, the number of chewing cycles associated with a given food, and food mechanical properties, should inform the broader question of which foods and feeding behaviors are most influential on the mandibular loading environment.     

Australopithecines: Ancestors of the African Apes?

Since australopithecines display humanlike traits such as short ilia, relatively small front teeth and thick molar enamel, they are usually assumed to be related toHomo rather than toPan orGorilla. However, this assumption is not supported by many other of their features. This paper briefly surveys the literature concerning craniodental comparisons of australopith species with those of bonobos, common chimps, humans and gorillas, adult and immature. It will be argued, albeit on fragmentary data, that the large australopiths of East Africa were in many instances anatomically and therefore possibly also evolutionarily nearer toGorilla than toPan orHomo, and the South African australopiths nearer toPan andHomo than toGorilla. An example of a possible evolutionary tree is provided. It is suggested that the evidence concerning the relation of the different australopithecines with humans, chimpanzees and gorillas should be re-evaluated.     

Linking Laboratory and Field Approaches in Studying the Evolutionary Physiology of Biting in Bamboo Lemurs

A realistic understanding of primate morphological adaptations requires a multidisciplinary approach including experimental studies of physiological performance and field studies documenting natural behaviors and reproductive success. For primate feeding, integrative efforts combining experimental and ecological approaches are rare. We discuss methods for collecting maximum bite forces in the field as part of an integrated ecomorphological research design. Specifically, we compare maximum biting ability in 3 sympatric bamboo lemurs (Hapalemur simus, H. aureus, and H. griseus) at Ranomafana National Park, Madagascar to determine if biting performance contributes to the observed partitioning of a shared bamboo diet. We assessed performance by recording maximum bite forces via jaw-muscle stimulations in anesthetized subjects from each species. Behavioral observations and food properties testing show that the largest species, Hapalemur simus, consumes the largest and most mechanically challenging foods. Our results suggest that Hapalemur simus can generate larger bite forces on average than those of the 2 smaller species. However, the overlap in maximum biting ability between Hapalemur simus and H. aureus indicates that biting performance cannot be the sole factor driving dietary segregation. Though maximum bite force does not fully explain dietary segregation, we hypothesize that size-related increases in both maximum bite force and jaw robusticity provide Hapalemur simus with an improved ability to process routinely its more obdurate diet. We demonstrate the feasibility of collecting physiological, ecological, and morphological data on the same free-ranging primates in their natural habitats. Integrating traditionally laboratory-based approaches with field studies broadens the range of potential primate species for physiological research and fosters improved tests of hypothesized feeding adaptations.     

Functional morphology of the cranio‐mandibular complex of the Guira cuckoo (Aves)

The cranio‐mandibular complex is an important structure involved in food capture and processing. Its morphology is related to the nature of the food item. Jaw muscles enable the motion of this complex and their study is essential for functional and evolutionary analysis. The present study compares available behavioral and dietary data obtained from the literature with novel results from functional morphological analyses of the cranio‐mandibular complex of the Guira cuckoo (Guira guira) to understand its relationship with the zoophagous trophic habit of this species. The bite force was estimated based on muscle dissections, measurements of the physiological cross‐sectional area, and biomechanical modeling of the skull. The results were compared with the available functional morphological data for other birds. The standardized bite force of G. guira is higher than predicted for exclusively zoophagous birds, but lower than for granivorous and/or omnivorous birds. Guira guira possesses the generalized jaw muscular system of neognathous birds, but some features can be related to its trophic habit. The external adductor muscles act mainly during food item processing and multiple aspects of this muscle group are interpreted to increase bite force, that is, their high values of muscle mass, their mechanical advantage (MA), and their perpendicular orientation when the beak is closed. The m. depressor mandibulae and the m. pterygoideus dorsalis et ventralis are interpreted to prioritize speed of action (low MA values), being most important during prey capture. The supposed ecological significance of these traits is the potential to widen the range of prey size that can be processed and the possibility of rapidly capturing agile prey through changes in the leverage of the muscles involved in opening and closing of the bill. This contributes to the trophic versatility of the species and its ability to thrive in different habitats, including urban areas.     

The Hadropithecus conundrum reconsidered, with implications for interpreting diet in fossil hominins

The fossil 'monkey lemur' Hadropithecus stenognathus has long excited palaeontologists because its skull bears an astonishing resemblance to those of robust australopiths, an enigmatic side branch of the human family tree. Multiple lines of evidence point to the likelihood that these australopiths ate at least some 'hard', stress-limited food items, but conflicting data from H. stenognathus pose a conundrum. While its hominin-like craniofacial architecture is suggestive of an ability to generate high bite forces, details of its tooth structure suggest that it was not well equipped to withstand the forces imposed by cracking hard objects. Here, we use three-dimensional digital reconstructions and finite-element analysis to test the hard-object processing hypothesis. We show that Archaeolemur sp. cf. A. edwardsi, a longer-faced close relative of H. stenognathus that lacked hominin convergences, was probably capable of breaking apart large, stress-limited food items, while Hadropithecus was better suited to processing small, displacement-limited (tougher but more compliant) foods. Our suggestion that H. stenognathus was not a hard-object feeder has bearing on the interpretation of hominin cranial architecture; the features shared by H. stenognathus and robust australopiths do not necessarily reflect adaptations for hard-object processing.     

Brain size at birth throughout human evolution: a new method for estimating neonatal brain size in hominins

An increase in brain size is a hallmark of human evolution. Questions regarding the evolution of brain development and obstetric constraints in the human lineage can be addressed with accurate estimates of the size of the brain at birth in hominins. Previous estimates of brain size at birth in fossil hominins have been calculated from regressions of neonatal body or brain mass to adult body mass, but this approach is problematic for two reasons: modern humans are outliers for these regressions, and hominin adult body masses are difficult to estimate. To accurately estimate the brain size at birth in extinct human ancestors, an equation is needed for which modern humans fit the anthropoid regression and one in which the hominin variable entered into the regression equation has limited error. Using phylogenetically sensitive statistics, a resampling approach, and brain-mass data from the literature and from National Primate Research Centers on 362 neonates and 2802 adults from eight different anthropoid species, we found that the size of the adult brain can strongly predict the size of the neonatal brain (r² = 0.97). This regression predicts human brain size, indicating that humans have precisely the brain size expected as an adult given the size of the brain at birth. We estimated the size of the neonatal brain in fossil hominins from a reduced major axis regression equation using published cranial capacities of 89 adult fossil crania. We suggest that australopiths gave birth to infants with cranial capacities that were on average 180 cc (95% CI: 158–205 cc), slightly larger than the average neonatal brain size of chimpanzees. Neonatal brain size increased in early Homo to 225 cc (95% CI: 198–257 cc) and in Homo erectus to approximately 270 cc (95% CI: 237–310 cc). These results have implications for interpreting the evolution of the birth process and brain development in all hominins from the australopiths and early Homo, through H. erectus, to Homo sapiens.     

Scaling of feeding biomechanics in the horn shark Heterodontus francisci: ontogenetic constraints on durophagy

Organismal performance changes over ontogeny as the musculoskeletal systems underlying animal behavior grow in relative size and shape. As performance is a determinant of feeding ecology, ontogenetic changes in the former can influence the latter. The horn shark Heterodontus francisci consumes hard-shelled benthic invertebrates, which may be problematic for younger animals with lower performance capacities. Scaling of feeding biomechanics was investigated in H. francisci (n=16, 19–59 cm standard length (SL)) to determine the biomechanical basis of allometric changes in feeding performance and whether this performance capacity constrains hard-prey consumption over ontogeny. Positive allometry of anterior (8–163 N) and posterior (15–382 N) theoretical bite force was attributed to positive allometry of cross-sectional area in two jaw adducting muscles and mechanical advantage at the posterior bite point (0.79–1.26). Mechanical advantage for anterior biting scaled isometrically (0.52). Fracture forces for purple sea urchins Strongylocentrotus purpuratus consumed by H. francisci ranged from 24 to 430 N. Comparison of these fracture forces to the bite force of H. francisci suggests that H. francisci is unable to consume hard prey early in its life history, but can consume the majority of S. purpuratus by the time it reaches maximum size. Despite this constraint, positive allometry of biting performance appears to facilitate an earlier entry into the durophagous niche than would an isometric ontogenetic trajectory. The posterior gape of H. francisci is significantly smaller than the urchins capable of being crushed by its posterior bite force. Thus, the high posterior bite forces of H. francisci cannot be fully utilized while consuming prey of similar toughness and size to S. purpuratus, and its potential trophic niche is primarily determined by anterior biting capacity.     

First Early Hominin from Central Africa (Ishango,Democratic Republic of Congo)

Despite uncontested evidence for fossils belonging to the early hominin genus Australopithecus in East Africa from at least 4.2 million years ago (Ma), and from Chad by 3.5 Ma, thus far there has been no convincing evidence of Australopithecus, Paranthropus or early Homo from the western (Albertine) branch of the Rift Valley. Here we report the discovery of an isolated upper molar (#Ish25) from the Western Rift Valley site of Ishango in Central Africa in a derived context, overlying beds dated to between ca. 2.6 to 2.0 Ma. We used µCT imaging to compare its external and internal macro-morphology to upper molars of australopiths, and fossil and recent Homo. We show that the size and shape of the enamel-dentine junction (EDJ) surface discriminate between Plio-Pleistocene and post-Lower Pleistocene hominins, and that the Ishango molar clusters with australopiths and early Homo from East and southern Africa. A reassessment of the archaeological context of the specimen is consistent with the morphological evidence and suggest that early hominins were occupying this region by at least 2 Ma.     

Experimental analysis of temporomandibular joint reaction force in macaques

Mandibular bone strain in the region immediately below the temporomandibular ligament was analyzed in adult and sub-adult Macaca fascicularis and Macaca mulatta. Following recovery from the general anesthetic, the monkeys were presented food objects, a wooden rod, or a specially designed bite-force transducer. Bone strain was recorded during incisal biting and mastication of food, and also during isometric biting of the rod and/or the transducer. The bone strain data suggest the following: The macaque TMJ is loaded by a compressive reaction force during the power stroke of mastication and incision of food, and during isometric molar and incisor biting. TMJ reaction forces are larger on the contralateral side during both mastication and isometric molar biting. Patterns of ipsilateral TMJ reaction force in macaques during isometric biting vary markedly in response to the position of the bite point. During biting along the premolars or first two molars a compressive reaction force acts about the ipsilateral TMJ; however, when the bite point is positioned along the M3, the ipsilateral TMJ has either very little compressive stress, no stress, or it is loaded in tension.     

The Evolutionary History of the Australopiths

The australopiths are a group of early hominins (humans and their close extinct relatives) that lived in Africa between approximately 4.1 and 1.4 million years ago. Formerly known as the australopithecines, they are not a “natural” group, in that they do not represent all of the descendants of a single common ancestor (i.e., they are not a “clade”). Rather, they are grouped together informally because nearly all share a similar adaptive grade (i.e., they have similar adaptations). In particular, they are bipedal apes that, to a greater or lesser extent, exhibit enlarged molar and premolar teeth (postcanine megadontia) and other associated modifications to their feeding apparatuses. Dietary adaptations clearly played an important role in shaping their evolutionary history. They also are distinguished by their lack of derived features typically associated with the genus Homo, such as a large brain, a broad complement of adaptations for manual dexterity, and advanced tool use. However, Homo is almost certainly descended from an australopith ancestor, so at least one or some australopiths belong directly to the human lineage. Regardless, australopiths had a rich evolutionary history deserving of study independent of questions about our direct ancestry. They were diverse, geographically widespread, and anatomically derived, they lived through periods of pronounced climate change, and their story dominates the narrative of human evolution for millions of years.     

Seed-breaking forces exerted by orang-utans with their teeth in captivity and a new technique for estimating forces produced in the Wild

Orang-utans (Pongo pygmaeus) at the Singapore Zoological Gardens were presented with two thick-shelled edible seeds, Mezzettia parviflora (Annonaceae) and Macadamia ternifolia (Proteaceae) in order to estimate their maximum bite forces. The orang-utans could break the Macadamia seeds in one bite, while those of Mezzettia required repeated attempts. Examination of shell fragments showed that many had scratches and some had clear, but small (ca. 1–2 mm diameter), impressions on them. Building upon this information, semi-imitative tests were performed on the seeds in a universal testing machine by loading them in compression with either flat plates or metal casts of orang-utan cheek teeth. The maximum forces required to break the seeds were similar with both the flat plates and the metal teeth; the average for the Macadamia seeds being about 2,000 N (which forms a minimum estimate for the maximum bite forces in orang-utans) and for the Mezzettia seeds, 6,000 N. The work done with the metal teeth was much greater than with the plates. A mechanical analysis showed that this extra work went into producing permanent impressions (“bite marks”) in the shell with the tooth cusps. These impressions were larger than those found on the shells of seeds bitten by the orang-utans. Nevertheless, it is shown theoretically that the size of these indentations can give an estimate of the bite forces used. The maximum force developed in the machine tests with the metal teeth was correlated with the force calculated from analysis of the bite marks. The method is suitable for use in field studies where the marks left on remnants of hard foods eaten by primates may be used to estimate, very roughly, the forces used to produce them. © 1994 Wiley-Liss, Inc.     

Cranial functional morphology of fossil dogs and adaptation for durophagy in Borophagus and Epicyon (Carnivora,Mammalia)

Morphological specialization is a complex interplay of adaptation and constraint, as similarly specialized features often evolve convergently in unrelated species, indicating that there are universally adaptive aspects to these morphologies. The evolutionary history of carnivores offers outstanding examples of convergent specialization. Among larger predators, borophagine canids were highly abundant during the tertiary of North America and are regarded as the ecological vicars of Afro‐Eurasian hyenas. Borophaginae is an extinct group of 60+ species, the largest forms evolving robust skulls with prominently domed foreheads, short snouts, and hypertrophied fourth premolars. These specializations have been speculated to enhance bone cracking. To test the extent that the skulls of derived borophagines were adapted for producing large bite forces and withstanding the mechanical stresses associated with bone cracking relative to their nonrobust sister clades, we manipulated muscle forces in models of six canid skulls and analyzed their mechanical response using 3D finite element analysis. Performance measures of bite force production efficiency and deformation minimization showed that skulls of derived borophagines Borophagus secundus and Epicyon haydeni are particularly strong in the frontal region; maximum stresses are lower and more evenly distributed over the skull than in other canids. Frontal strength is potentially coupled with a temporalis‐driven bite to minimize cranial stress during biting in the two derived genera, as tensile stress incurred by contracting temporalis muscles is dissipated rostro‐ventrally across the forehead and face. Comparison of estimated masticatory muscle cross section areas suggests that the temporalis‐masseter ratio is not strongly associated with morphological adaptations for bone cracking in Borophagus and Epicyon; larger body size may explain relatively larger temporalis muscles in the latter. When compared with previous studies, the overall cranial mechanics of the derived borophagines is more similar to bone‐cracking hyaenids and percrocutids than to their canid relatives, indicating convergence in both morphological form and functional capability. J. Morphol., 2010. © 2010 Wiley‐Liss, Inc.     

Comparative finite element analysis of the cranial performance of four herbivorous marsupials

Marsupial herbivores exhibit a wide variety of skull shapes and sizes to exploit different ecological niches. Several studies on teeth, dentaries, and jaw adductor muscles indicate that marsupial herbivores exhibit different specializations for grazing and browsing. No studies, however, have examined the skulls of marsupial herbivores to determine the relationship between stress and strain, and the evolution of skull shape. The relationship between skull morphology, biomechanical performance, and diet was tested by applying the finite element method to the skulls of four marsupial herbivores: the common wombat (Vombatus ursinus), koala (Phascolarctos cinereus), swamp wallaby (Wallabia bicolor), and red kangaroo (Macropus rufus). It was hypothesized that grazers, requiring stronger skulls to process tougher food, would have higher biomechanical performance than browsers. This was true when comparing the koala and wallaby (browsers) to the wombat (a grazer). The cranial model of the wombat resulted in low stress and high mechanical efficiency in relation to a robust skull capable of generating high bite forces. However, the kangaroo, also a grazer, has evolved a very different strategy to process tough food. The cranium is much more gracile and has higher stress and lower mechanical efficiency, but they adopt a different method of processing food by having a curved tooth row to concentrate force in a smaller area and molar progression to remove worn teeth from the tooth row. Therefore, the position of the bite is crucial for the structural performance of the kangaroo skull, while it is not for the wombat which process food along the entire tooth row. In accordance with previous studies, the results from this study show the mammalian skull is optimized to resist forces generated during feeding. However, other factors, including the lifestyle of the animal and its environment, also affect selection for skull morphology to meet multiple functional demands. J. Morphol. 276:1230–1243, 2015. © 2015 Wiley Periodicals, Inc.     

Biomechanics of the masticatory apparatus of Pteropus giganteus (Megachiroptera)

Jaw mechanics in Pteropus were studied by means of a three-dimensional model. The model included several parameters of muscle architecture, combined with quantified movement and electromyographical data. Estimates of the nature of the applied forces that act upon the mandible during a chewing cycle, and subsequent estimates of reaction forces at the bite point and joints during the powerstroke, were thus obtained for different food consistencies. The resultant muscle force (relative to the palate) shifts from upward and slightly backward at large gapes to upward and markedly backward at the end of closing. The resultant simultaneously moves anteriorly. During the powerstroke it retains a constant position and orientation along the thickened anterior edge of the coronoid process. The early stages of opening are guided by the slope of the teeth and mandibular fossa; during the remaining part of opening the working line of the resultant crosses the skull behind the joint and thus acquires an opening moment. The bite force has downward and forward components, and a slight transverse component. For a given applied muscular force its magnitude is larger in more posteriorly positioned bite points. Both joints are loaded, the contralateral one more than the ipsilateral. Food consistency affects magnitude and orientation of the applied force, and hence, magnitude and orientation of the bite force and magnitude of the joint reaction forces. The magnitude of masseter activity relative to temporalis activity appears to be the key factor for the orientation of the bite force, and hence for the mechanical optimal position of the food. The adaptive value of the general topography of the masticatory muscles in Pteropus is discussed.     

Application and validation of a three-dimensional mathematical model of the human masticatory system in vivo.

A previously described three-dimensional mathematical model of the human masticatory system, predicting maximum possible bite forces in all directions and the recruitment patterns of the masticatory muscles necessary to generate these forces, was validated in in vivo experiments. The morphological input parameters to the model for individual subjects were collected using MRI scanning of the jaw system. Experimental measurements included recording of maximum voluntary bite force (magnitude and direction) and surface EMG from the temporalis and masseter muscles. For bite forces with an angle of 0, 10 and 20 degrees relative to the normal to the occlusal plane the predicted maximum possible bite forces were between 0.9 and 1.2 times the measured ones and the average ratio of measured to predicted maximum bite force was close to unity. The average measured and predicted muscle recruitment patterns showed no striking differences. Nevertheless, some systematic differences, dependent on the bite force direction, were found between the predicted and the measured maximum possible bite forces. In a second series of simulations the influence of the direction of the joint reaction forces on these errors was studied. The results suggest that they were caused primarily by an improper determination of the joint force directions.     

Mosaic functionality in a transitional ecomorphology: skull biomechanics in stem Hyaeninae compared to modern South African carnivorans

Ecomorphologies are categories of ecological adaptation and function, although intermediates are not always available to shed light on functionality at the transitional stages between them. We examined an intermediate bone‐cracking carnivoran ecomorphology, the stem hyaenine Ikelohyaena abronia, using finite element analysis. Skull models of Ikelohyaena, crown hyaenine Crocuta crocuta, and two other hypercarnivores were simulated with mastication and prey apprehension forces. The results obtained show that Ikelohyaena already possessed derived features in skull stress distribution and levels of strain energy, characteristic of the extant bone‐cracking Crocuta; however, the estimated bite forces in Ikelohyaena were significantly lower. Prey apprehension simulations showed similar patterns; the low skull strain energy and low bite force of the Ikelohyaena mandible indicate a poor individual ability to take down large prey. The mosaic features of craniodental function in Ikelohyaena suggest that initial evolution of the hyaenid bone‐cracking ecomorphology involved skull shape changes that increased stress dissipation, permitting incorporation of more hard food into the diet. Subsequent evolution of larger bite forces was then required to increase the size limit of bones that can be cracked and consumed. This mode of evolution would have allowed transitional hyaenid ecomorphologies to continuously increase the carcass processing ability both during competitive feeding and scavenging throughout their evolution. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 540–559.     

Tooth root morphology as an indicator for dietary specialization in carnivores (Mammalia: Carnivora)

The Carnivora occupy a wide range of feeding niches in concordance with the enormous diversity in their skull and dental form. It is well established that differences in crown morphology are linked to variations in the material properties of the foods ingested and masticated. However, how tooth root form is related to dietary specialization is less well known. In the present study, we investigate the relationship between tooth root morphology and dietary specialization in terrestrial carnivores (canids, felids, hyaenids, and ursids). We specifically address the question of how variation in tooth root surface area is related to bite force potentials as one of the crucial masticatory performance parameters in feeding ecology. We applied computed tomography imaging to reconstruct and quantify dental root surface area in 17 extant carnivore species. Moreover, we computed maximal bite force at several tooth positions based on a dry skull model and assessed the relationship of root surface area to skull size, maximal bite force, food properties, and prey size. We found that postcanine tooth root surface areas corrected for skull size serve as a proxy for bite force potentials and, by extension, dietary specialization in carnivores. Irrespective of taxonomic affinity, species that feed on hard food objects have larger tooth roots than those that eat soft or tough foods. Moreover, carnivores that prey on large animals have larger tooth root surface areas. Our results show that tooth root morphology is a useful indicator of bite force production and allows inferences to be made about dietary ecology in both extant and extinct mammals. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105, 456–471.     

Under pressure: morphological and ecological correlates of bite force in the rock‐dwelling lizards Ouroborus cataphractus and Karusasaurus polyzonus (Squamata: Cordylidae)

Rock‐dwelling lizards are hypothesized to be highly constrained in the evolution of head morphology and, consequently, bite force. Because the ability to generate a high bite force might be advantageous for a species' dietary ecology, morphological changes in head configuration that allow individuals to maintain or improve their bite force under the constraint of crevice‐dwelling behaviour are to be expected. The present study addressed this issue by examining head morphology, bite force, and a number of dietary traits in the rock‐dwelling cordylid lizards Ouroborus cataphractus and Karusasaurus polyzonus. The results obtained show that O. cataphractus has a larger head and higher bite force than K. polyzonus. In K. polyzonus, head width, lower jaw length, and jaw closing‐in lever are the best predictors of bite force, whereas head height is the main determinant of bite force in O. cataphractus. Although the observed difference in bite force between the species does not appear to be related to dietary patterns or prey handling, the prey spectrum available for intake was greater in O. cataphractus compared to K. polyzonus. We discuss the influence of interspecific differences in anti‐predator morphology on head morphology and bite force in these rock‐dwelling species. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111, 823–833.