Tooth Root Morphology in the Early Pliocene African Bear Agriotherium africanum (Mammalia, Carnivora, Ursidae) and its Implications for Feeding Ecology

Tooth root surface areas serve as proxies for bite force potentials, and by extension, dietary specialization in extant carnivorans. Here, we investigate the feeding ecology of the extinct large-bodied ursid Agriotherium africanum, by comparing its root surface areas (reconstructed with the aid of computed tomography and three-dimensional image processing) and bite force estimates, with those of extant carnivorans. Results show that in absolute terms, canine and carnassial bite forces, as well as root surface areas were highest in A. africanum. However, when adjusted for skull size, A. africanum’s canine roots were smaller than those of extant solitary predators. With teeth being the limiting factor in the masticatory system, low canine root surface areas suggest that A. africanum would have struggled to bring down large vertebrate prey. Its adjusted carnassial root sizes were found to be smaller than those of extant hard object feeders and the most carnivorous tough object feeders, but larger than those of extant omnivorous ursids and Ursus maritimus. This and the fact that it displayed its highest postcanine root surface areas in the carnassial region (rather than the most distal tooth in the tooth row) suggest that A. africanum consumed more vertebrate tissue than extant omnivorous ursids. With an apparent inability to routinely bring down large prey or to consume mechanically demanding skeletal elements, its focus was most likely on tough tissue, which it acquired by actively scavenging the carcasses of freshly dead/freshly killed animals. Mechanically less demanding skeletal elements would have been a secondary food source, ingested and processed mainly in association with muscle and connective tissue.     

Dental root size in bats with diets of different hardness

The relationship between tooth roots and diet is relatively unexplored, although a logical relationship between harder diets and increased root surface area (RSA) is suggested. This study addresses the interaction between tooth morphology, diet, and bite force in small mammals, phyllostomid bats. Using micro computed tomography (microCT), tooth root morphology of two fruit‐eating species (Carollia perspicillata and Chiroderma villosum) and two insect‐eating species (Mimon bennettii and Macrotus californicus) was compared. These species did not differ in skull or estimated body size. Food hardness, rather than dietary classification, proved to be the strongest grouping factor, with the two insectivores and the seed‐processing frugivore (C. villosum) having significantly larger RSAs. Bite force was estimated using skull measurements; bite force significantly correlated with tooth RSA but not with body size. Although the three durophagous species did exhibit larger crowns, the area of the occlusal surface did not vary among the four species. There was a linear relationship between root size and crown size, indicating that the roots were not expanded disproportionately; instead the entire tooth was larger in the hard diet species. MicroCT allows the nondestructive quantification of previously difficult‐to‐access tooth morphology; this method shows the potential for tooth roots to provide valuable dietary, behavioral, and ecological information in small mammals. J. Morphol. 276:1065–1074, 2015. © 2015 Wiley Periodicals, Inc.     

Ecological consequences of ontogenetic changes in head shape and bite performance in the Jamaican lizard Anolis lineatopus

It has been documented extensively that body size affects the physiology and musculoskeletal function of organisms. However, less well understood is how body size affects the ecology of organisms through its effects on physiology and performance. We explored the effects of body size on morphology and performance in different ontogenetic classes and sexes of a common Anolis lizard ( A. lineatopus ). Next, we tested whether these morphological and performance differences may affect functional aspects of the diet such as prey size and prey hardness. Our data showed that males, females and juveniles differ significantly in head size, head shape and bite force. Multiple regression models indicated that head shape and bite force are significantly correlated to prey size and hardness. Yet juveniles had relatively large heads and bit disproportionately hard for their size, allowing them to eat prey as large as those of females. However, for a given prey size, males and females ate more robust prey than did juveniles. Additionally, males ate relatively harder prey than did juveniles. These data suggest that: (1) body size affects the dietary ecology of animals through its effect on head size and bite force; (2) changes in head morphology independent of changes in overall size also have important effects on performance and diet.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 443–454.     

Comparative bite forces and canine bending strength in feline and sabretooth felids: implications for predatory ecology

The sabretooth felids were widespread across much of the world in the Late Tertiary, and appear to have been an important group of large predators. Owing to the substantially different skull morphology of derived sabretooths compared with extant felids, there has been considerable debate over the killing mode, bite forces, and bending strength of the large upper canines, and over the implications of these characteristics on feeding ecology. Debates have, however, usually been based on indirect comparisons of force vectors. In this paper, I provide assessments of the estimated force output from the jaw adductor muscles, based on estimates of muscle cross-sectional areas and force vectors, along with canine bending strengths, in a variety of sabretooth felids, in comparison with extant felids. In general, sabretoothed felids had moderately powerful bites, albeit with less jaw adductor power for their body sizes compared with extant felids, sometimes markedly so. Less derived sabrecats appear to have had proportionally higher bite forces than derived forms. The length of the upper canines seemingly compromised their bending strength at any given body size, and again this was most marked in derived forms. However, compared with estimated jaw adductor forces, the canines of sabrecats appear, if anything, to have been stronger than those of extant conical-toothed felids. It has previously been suggested that large sabretoothed felids hunted large prey with a canine shearing bite, powered in part by the jaw adductors and in part by the muscles of the upper neck–occipital region. The present results of canine bending strengths versus the predicted bite force from the jaw adductors supports this suggestion.  © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society , 2007, 151 , 423–437.     

Correlations between lizard cranial shape and diet: a quantitative, phylogenetically informed analysis

Although the relationship between dietary and phenotypic specialization has been well documented for many vertebrate groups, it has been stated that few such general trends can be established for lizards. This is often thought to be due to the lack of dietary specialization in many lizards. For example, many species that are reported to be insectivorous may also consume a variety of plant materials, and the reverse is often true as well. In this study, we investigate whether a correlation exists between general cranial form and dietary niche in lizards. Additionally, we test previously proposed hypotheses suggesting that herbivorous lizards should be larger bodied than lizards with other diets. Our data indicate that lizards specializing in food items imposing different mechanical demands on the feeding system show clear patterns of morphological specialization in their cranial morphology. True herbivores (diet of fibrous and tough foliage) are clearly distinguished from omnivorous and carnivorous lizards by having taller skulls and shorter snouts, likely related to the need for high bite forces. This allows herbivores to mechanically reduce relatively less digestible foliage. Carnivores have relatively longer snouts and retroarticular processes, which may result in more efficient capture and processing of elusive prey. When analysed in an explicit phylogenetic context, only snout length and skull mass remained significantly different between dietary groups. The small number of differences in the phylogenetic analyses is likely the result of shared evolutionary history and the relative paucity of independent origins of herbivory and omnivory in our sample. Analyses of the relationship between diet and body size show that on average herbivores have a larger body size than carnivores, with omnivores intermediate between the two other dietary groups. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 86 , 433–466.     

Cricetid rodents: Is molar root morphology an indicator of diet?

The relationship between tooth roots and diet is largely unexplored, although a logical relationship between harder diets and increased root surface area is suggested. Existing studies of primates, carnivorans and phyllostomid bats have indicated a relationship between diet hardness, bite force and tooth root surface area. The goal of this study was to determine whether root surface area can act as a potential surrogate for bite force and diet in cricetid rodents. Using microcomputed tomography (microCT), tooth root morphology from six species of rodents, two grass eaters (Calomys callosus and Reithrodon auritus), two seed eaters (Phyllotis darwini and Ochrotomys nuttalli) and two insect eaters (Akodon azarae and Oxymycterus hispidus) were compared. Similar to other studies, these rodents did exhibit differences in tooth root surface area based on diet classification, but food hardness did not seem to be a factor. Grass-eating species showed significantly larger roots relative to the other diet groups (p = 0.001). Bite force was estimated using skull measurements. Seed eaters were found to have a larger bite force, followed by grass and insect eaters, though the trend did not reach statistical significance (p = 0.058). No strong relationship was found between estimated bite force and tooth root surface area. In this study, the mechanics of grass eating seem to have a stronger effect on tooth root surface area than bite force. microCT allows the nondestructive quantification of previously difficult-to-access tooth morphology; this method shows the potential for tooth roots to provide valuable dietary, behavioral and ecological information in rodents.     

Morphology and mechanics of the teeth and jaws of white-spotted bamboo sharks (Chiloscyllium plagiosum)

The teeth of white-spotted bamboo sharks (Chiloscyllium plagiosum) are used to clutch soft-bodied prey and crush hard prey; however, the dual function is not evident from tooth morphology alone. Teeth exhibit characteristics that are in agreement with a clutching-type tooth morphology that is well suited for grasping and holding soft-bodied prey, but not for crushing hard prey. The dual role of this single tooth morphology is facilitated by features of the dental ligament and jaw joint. Tooth attachment is flexible and elastic, allowing movement in both sagittal and frontal planes. During prey capture spike-like tooth cusps pierce the flesh of soft prey, thereby preventing escape. When processing prey harder than the teeth can pierce the teeth passively depress, rotating inward towards the oral cavity such that the broader labial faces of the teeth are nearly parallel to the surface of the jaws and form a crushing surface. Movement into the depressed position increases the tooth surface area contacting prey and decreases the total stress applied to the tooth, thereby decreasing the risk of structural failure. This action is aided by a jaw joint that is ventrally offset from the occlusal planes of the jaws. The offset joint position allows many teeth to contact prey simultaneously and orients force vectors at contact points between the jaws and prey in a manner that shears or rolls prey between the jaws during a bite, thus, aiding in processing while reducing forward slip of hard prey from the mouth. Together the teeth, dental ligament, and jaws form an integrated system that may be beneficial to the feeding ecology of C. plagiosum, allowing for a diet that includes prey of varying hardness and elusiveness.     

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.     

Carnivory maintains cranial dimorphism between males and females: Evidence for niche divergence in extant Musteloidea

The evolution and maintenance of sexual dimorphism has long been attributed to sexual selection. Niche divergence, however, serves as an alternative but rarely tested selective pressure also hypothesized to drive phenotypic disparity between males and females. We reconstructed ancestral social systems and diet and used Ornstein–Uhlenbeck (OU) modeling approaches to test whether niche divergence is stronger than sexual selection in driving the evolution of sexual dimorphism in cranial size and bite force across extant Musteloidea. We found that multipeak OU models favored different dietary regimes over social behavior and that the greatest degree of cranial size and bite force dimorphism were found in terrestrial carnivores. Because competition for terrestrial vertebrate prey is greater than other dietary groups, increased cranial size and bite force dimorphism reduces dietary competition between the sexes. In contrast, neither dietary regime nor social system influenced the evolution of sexual dimorphism in cranial shape. Furthermore, we found that the evolution of sexual dimorphism in bite force is influenced by the evolution of sexual dimorphism in cranial size rather than cranial shape. Overall, our results highlight niche divergence as an important mechanism that maintains the evolution of sexual dimorphism in musteloids.     

Insights into the ecology and evolutionary success of crocodilians revealed through bite-force and tooth-pressure experimentation

Background

Crocodilians have dominated predatory niches at the water-land interface for over 85 million years. Like their ancestors, living species show substantial variation in their jaw proportions, dental form and body size. These differences are often assumed to reflect anatomical specialization related to feeding and niche occupation, but quantified data are scant. How these factors relate to biomechanical performance during feeding and their relevance to crocodilian evolutionary success are not known.

Methodology/Principal Findings

We measured adult bite forces and tooth pressures in all 23 extant crocodilian species and analyzed the results in ecological and phylogenetic contexts. We demonstrate that these reptiles generate the highest bite forces and tooth pressures known for any living animals. Bite forces strongly correlate with body size, and size changes are a major mechanism of feeding evolution in this group. Jaw shape demonstrates surprisingly little correlation to bite force and pressures. Bite forces can now be predicted in fossil crocodilians using the regression equations generated in this research.

Conclusions/Significance

Critical to crocodilian long-term success was the evolution of a high bite-force generating musculo-skeletal architecture. Once achieved, the relative force capacities of this system went essentially unmodified throughout subsequent diversification. Rampant changes in body size and concurrent changes in bite force served as a mechanism to allow access to differing prey types and sizes. Further access to the diversity of near-shore prey was gained primarily through changes in tooth pressure via the evolution of dental form and distributions of the teeth within the jaws. Rostral proportions changed substantially throughout crocodilian evolution, but not in correspondence with bite forces. The biomechanical and ecological ramifications of such changes need further examination.     

Functional and ecological relevance of intraspecific variation in body size and shape in the lizard Podarcis melisellensis (Lacertidae)

Within populations, individual animals may vary considerably in morphology and ecology. The degree to which variation in morphology is related to ecological variation within a population remains largely unexplored. We investigated whether variation in body size and shape among sexes and age classes of the lizard Podarcis melisellensis translates in differential whole-animal performance (sprint speed, bite force), escape and prey attack behaviour in the field, microhabitat use and diet. Male and female adult lizards differed significantly in body size and head and limb proportions. These morphological differences were reflected in differences in bite strength, but not in sprint speed. Accordingly, field measurements of escape behaviour and prey attack speed did not differ between the sexes, but males ate larger, harder and faster prey than females. In addition to differences in body size, juveniles diverged from adults in relative limb and head dimensions. These shape differences may explain the relatively high sprint and bite capacities of juvenile lizards. Ontogenetic variation in morphology and performance is strongly reflected in the behaviour and ecology in the field, with juveniles differing from adults in aspects of their microhabitat use, escape behaviour and diet.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 251–264.     

Comparative observations on the tooth root morphology of Gigantopithecus blacki

The extinct great ape Gigantopithecus blacki from the middle Pleistocene of China and Vietnam is known only from dental and mandibular remains, and its dietary specializations remain contentious. Here, for the first time, we describe the root morphology in G. blacki using computed tomography and three-dimensional image processing. We quantify the tooth root lengths and surface areas of the female G. blacki mandible No. 1 from the Liucheng Cave and compare it to a sample of extant great apes and humans, as well as the giant panda (Ailuropoda melanoleuca) and the American black bear (Ursus americanus). The results show that, in G. blacki, the pattern of mandibular root numbers-particularly that of the premolars-corresponds with that of Gorilla gorilla, Pan troglodytes, and Pongo pygmaeus. However, G. blacki can be distinguished from the extant hominids by having relatively higher values for postcanine root length and surface area, both absolutely and relative to mandibular size (except for premolar root lengths of humans). The relatively large postcanine root surface areas, which are most similar to A. melanoleuca, suggest that the dentition of G. blacki was adapted to sustaining relatively large occlusal forces needed to fracture mechanically resistant foods such as bamboo.     

Tooth Chipping as a Tool to Reconstruct Diets of Great Apes (Pongo, Gorilla, Pan)

Most methods of dietary reconstruction are limited in their applicability to either extant or extinct taxa. We apply and discuss a method in which dietary information can be reconstructed from chips in the tooth enamel of both living and fossil primates. Such chips can be used to indicate the presence of large hard foods in the diet, and also to provide an estimate of the bite force that was used when the chip was created. Furthermore, the equations derived from this method allow an estimate of maximum bite force to be obtained from a simple measurement of tooth size. We use this method to investigate dietary differences in nonhuman great apes (Pongo, Gorilla, Pan). The high frequency of chips on teeth of Pongo indicate that they frequently use high forces to process hard foods such as seeds and nuts. Gorilla can generate even higher bite forces, but their low incidence of tooth chips suggests that they do so when consuming soft but tough foods. Tooth chips provide a lasting dietary signal that is not easily masked or erased, making them particularly useful for the study of rarely eaten items such as some fallback foods.     

Skull morphology and functionality of extant Felidae (Mammalia: Carnivora): a phylogenetic and evolutionary perspective

Felids morphology and ecological role as hypercarnivores are quite constant, despite considerable body size variation among species. Skull morphological and functional features of 34 extant cat species were evaluated under a phylogenetic framework of the Felidae. Twenty skull measurements were analysed through Principal Component Analysis to assess the species morphofunctional spaces. Force indexes were obtained from static equilibrium equations to infer jaw mechanics. Correlations between morphological, functional, and ecological traits were tested by phylogenetically independent contrasts. In spite of the general cat‐like pattern, specific features on the skulls allowed differentiation among groups. Acinonyx jubatus, for instance, showed a shorter and shallower temporal fossa than other big cats, and their bite functionality is marked by an increased contribution of the masseteric system. A morphofunctional dichotomy between Neotropical and Eurasian/African small cats was detected, and is associated with the major transversal axes of the skulls. According to the contrast analyses, the skull size is correlated with the bite force and prey size, but it is uncorrelated with the variations on jaw mechanics (from temporalis or masseter muscle optimizations). Also, there was no correlation between functional differences on jaw muscles and the ratio of prey weight to cat weight. The efficiency of the jaw apparatus among cats is quite consistent; therefore, the different evolutionary trends of jaw mechanics seem to be caused by the casuistic fixation of phenotypical variations, rather than by specific adaptative selections. © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 161 , 414–462.     

Costs of carnivory: tooth fracture in Pleistocene and Recent carnivorans

Large, carnivorous mammals often break their teeth, probably as a result of tooth to bone contact that occurs when carcasses are consumed more fully, a behaviour likely to occur under conditions of food stress. Recent studies of Pleistocene predators revealed high numbers of teeth broken in life, suggesting that carcass utilization and, consequently, food competition was more intense in the past than at present. However, the putative association between diet and tooth fracture frequency was based on a small sample of large, highly carnivorous species. In the present study, a greater diversity of extant carnivorans is sampled, including insectivorous, omnivorous, and carnivorous forms, ranging in size from weasels to tigers. Species that habitually consume hard foods (bones, shells) had the highest fracture frequencies, followed by carnivores, and then insectivorous and/or omnivorous species. Predator and prey sizes were not associated with tooth fracture frequency, but more aggressive species did break their teeth more often. Comparison of the modern sample with five Pleistocene species confirms the previous finding of higher tooth breakage in the past, although some extant species have fracture frequencies that approach those of extinct species. Thus, the Pleistocene predator guild appears to have been characterized by relatively high levels of competition that are rarely observed today.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 68–81.     

Insularity affects head morphology,bite force and diet in a Mediterranean lizard

Island environments differ with regard to numerous features from the mainland and may induce large‐scale changes in most aspects of the biology of an organism. In this study, we explore the effect of insularity on the morphology and performance of the feeding apparatus, a system crucial for the survival of organisms. To this end, we examined the head morphology and feeding ecology of island and mainland populations of the Balkan green lizard, Lacerta trilineata. We predicted that head morphology, performance and diet composition would differ between sexes and habitats as a result of varying sexual and natural selection pressures. We employed geometric morphometrics to test for differences in head morphology, measured bite forces and analysed the diet of 154 adult lizards. Morphological analyses revealed significant differences between sexes and also between mainland and island populations. Relative to females, males had larger heads, a stronger bite and consumed harder prey than females. Moreover, island lizards differed in head shape, but not in head size, and, in the case of males, demonstrated a higher bite force. Islanders had a wider food niche breadth and included more plant material in their diet. Our findings suggest that insularity influences feeding ecology and, through selection on bite force, head morphology. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 112 , 469–484.     

Is dietary niche breadth linked to morphology and performance in Sandveld lizards Nucras (Sauria: Lacertidae)?

The functional characteristics of prey items (such as hardness and evasiveness) have been linked with cranial morphology and performance in vertebrates. In lizards particularly, species with more robust crania generally feed on harder prey items and possess a greater bite force, whereas those that prey on evasive prey typically have longer snouts. However, the link between dietary niche breadth, morphology, and performance has not been explicitly investigated in lizards. The southern African genus Nucras was used to investigate this link because the species exhibit differing niche breadth values and dietary compositions. A phylogeny for the genus was established using mitochondrial and nuclear markers, and morphological clusters were identified. Dietary data of five Nucras species, as reported previously, were used in correlation analyses between cranial shape (quantified using geometric morphometrics) and dietary niche breadth, and the proportion of hard prey taken and bite force capacity. Dietary niche breadth and the proportion of hard prey eaten were significantly related to cranial shape, although not once phylogeny was accounted for using a phylogenetic generalized least squares regression. The proportion of evasive prey eaten was a significant predictor of forelimb length when phylogeny was taken into account. We conclude that, in Nucras, the percentage of evasive prey taken co‐evolves with forelimb morphology, and dietary niche breadth co‐evolves with cranial shape. However, although head width is correlated with the proportion of hard prey eaten, this appears to be the result of shared ancestry rather than adaptive evolution. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 674–688.     

Dry versus wet and gross: Comparisons between the dry skull method and gross dissection in estimations of jaw muscle cross-sectional area and bite forces in sea otters

Bite force is a measure of feeding performance used to elucidate links between animal morphology, ecology, and fitness. Obtaining live individuals for in vivo bite-force measurements or freshly deceased specimens for bite force modeling is challenging for many species. Thomason's dry skull method for mammals relies solely on osteological specimens and, therefore, presents an advantageous approach that enables researchers to estimate and compare bite forces across extant and even extinct species. However, how accurately the dry skull method estimates physiological cross-sectional area (PCSA) of the jaw adductor muscles and theoretical bite force has rarely been tested. Here, we use an ontogenetic series of southern sea otters (Enhydra lutris nereis) to test the hypothesis that skeletomuscular traits estimated from the dry skull method accurately predicts test traits derived from dissection-based biomechanical modeling. Although variables from these two methods exhibited strong positive relationships across ontogeny, we found that the dry skull method overestimates PCSA of the masseter and underestimates PCSA of the temporalis. Jaw adductor in-levers for both jaw muscles and overall bite force are overestimated. Surprisingly, we reveal that sexual dimorphism in craniomandibular shape affects temporalis PCSA estimations; the dry skull method predicted female temporalis PCSA well but underestimates male temporalis PCSA across ontogeny. These results highlight the importance of accounting for sexual dimorphism and other intraspecific variation when using the dry skull method. Together, we found the dry skull method provides an underestimation of bite force over ontogeny and that the underlying anatomical components driving bite force may be misrepresented.     

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.     

Dietary constraints of phytosaurian reptiles revealed by dental microwear textural analysis

Phytosaurs are a group of large, semi‐aquatic archosaurian reptiles from the Middle–Late Triassic. They have often been interpreted as carnivorous or piscivorous due to their large size, morphological similarity to extant crocodilians and preservation in fluvial, lacustrine and coastal deposits. However, these dietary hypotheses are difficult to test, meaning that phytosaur ecologies and their roles in Triassic food webs remain incompletely constrained. Here, we apply dental microwear textural analysis to the three‐dimensional sub‐micrometre scale tooth surface textures that form during food consumption to provide the first quantitative dietary constraints for five species of phytosaur. We furthermore explore the impacts of tooth position and cranial robustness on phytosaur microwear textures. We find subtle systematic texture differences between teeth from different positions along phytosaur tooth rows, which we interpret to be the result of different loading pressures experienced during food consumption, rather than functional partitioning of food processing along tooth rows. We find rougher microwear textures in morphologically robust taxa. This may be the result of seizing and processing larger prey items compared to those captured by gracile taxa, rather than dietary differences per se. We reveal relatively low dietary diversity between our study phytosaurs and that individual species show a lack of dietary specialization. Species are predominantly carnivorous and/or piscivorous, with two taxa exhibiting slight preferences for ‘harder’ invertebrates. Our results provide strong evidence for higher degrees of ecological convergence between phytosaurs and extant crocodilians than previously appreciated, furthering our understanding of the functioning and evolution of Triassic ecosystems.