Taylor AB, 2002. Masticatory form and function in the African apes. Am J Phys Anthropol. 117, 133-156. (original) (raw)
Related papers
Taylor AB, 2006. Diet and mandibular morphology in the African apes. Int J Primatol. 27, 181-201.
Investigations seeking to understand the relationship between mandibular form, function, and dietary behavior have focused on the mandibular corpus and symphysis. African apes vary along a gradient of folivory/frugivory, yet few studies have evaluated the morphology of the mandibular corpus and symphysis in these taxa, and the investigations have yielded mixed results. Specifically, studies using external metrics have identified differences in mandibular proportions that analysis of cortical bone distribution has not substantiated. I contribute to the ongoing debate on the relationship between jaw form and dietary behavior by comparing mandibular corporal and symphyseal shapes in African apes. Importantly, and in contrast to previous studies of African ape internal geometry, I include the Virunga mountain gorillas (Gorilla beringei beringei), the ape most specialized toward a folivorous diet. I test the hypotheses that 1) Gorilla beringei beringei always has significantly more robust mandibular corpora and symphyses, relative to mandibular length, than all other African apes and 2) all gorillas have significantly more robust mandibular corpora and symphyses, relative to mandibular length, than Pan. Results demonstrate that the folivorous mountain gorillas consistently exhibit a relatively wider mandibular symphysis and corpus than all other African apes. Furthermore, all gorillas consistently exhibit relatively more robust mandibular corporal and symphyseal dimensions than Pan. The results indicate that among African apes, mountain gorillas are better able to counter lateral transverse bending (wishboning) loads at the symphysis and torsional loads at the corpus. All gorillas are likewise better able to resist wishboning and vertical bending at the symphysis, and sagittal bending and torsion at the corpus, than Pan, findings that are consistent with 182 Taylor masticating relatively tougher foods, repetitive loading of the jaws, or both. I offer possible explanations for the lack of concordance in results between studies that have analyzed the biomechanical properties of African ape mandibles and others that have relied on external metrics. More comprehensive study of the internal geometry of the mandible is needed to resolve whether African apes differ morphologically in ways predicted by dietary variation.
Primate dietary ecology in the context of food mechanical properties
Journal of human evolution, 2016
Substantial variation exists in the mechanical properties of foods consumed by primate species. This variation is known to influence food selection and ingestion among non-human primates, yet no large-scale comparative study has examined the relationships between food mechanical properties and feeding strategies. Here, we present comparative data on the Young's modulus and fracture toughness of natural foods in the diets of 31 primate species. We use these data to examine the relationships between food mechanical properties and dietary quality, body mass, and feeding time. We also examine the relationship between food mechanical properties and categorical concepts of diet that are often used to infer food mechanical properties. We found that traditional dietary categories, such as folivory and frugivory, did not faithfully track food mechanical properties. Additionally, our estimate of dietary quality was not significantly correlated with either toughness or Young's modulus....
Morphological adaptation to diet in platyrrhine primates
American Journal of Physical Anthropology, 1994
Morphological features of the jaws and teeth are examined in eight species of platyrrhine monkeys that coexist in the Suriname rainforest. Z-scores calculated from geometric predictions for several features of the feeding apparatus thought to have some functional significance (e.g., tooth dimensions, jaw robusticity, leverage of primary jaw elevators) are compared to a profile of the naturalistic dietary behavior of these species (i.e., proportions of fruit mesocarp, seeds, leaves, and fauna eaten).
Dietary correlates of temporomandibular joint morphology in the great apes
Behavioral observations of great apes have consistently identified differences in feeding behavior among species, and these differences have been linked to variation in masticatory form. As the point at which the mandible and cranium articulate, the temporomandibular joint (TMJ) is an important component of the masticatory apparatus. Forces are transmitted between the mandible and cranium via the TMJ, and this joint helps govern mandibular range of motion. This study examined the extent to which TMJ form covaries with feeding behavior in the great apes by testing a series of biomechanical hypotheses relating to specific components of joint shape using linear measurements extracted from three-dimensional coordinate data. Results of these analyses found that taxa differ significantly in TMJ shape, I use the term ''resistant'' here to collectively refer to foods that are fracture resistant (tough) and/or stress-limited (stiff) . in Wiley Online Library (wileyonlinelibrary.com).
Evolution, Constraint, and Optimality in Primate Feeding Systems
Feeding in Vertebrates, 2019
Evolutionary biomechanical studies of primate feeding systems have benefited from deployment of techniques for measurement of food material properties, digital collections of morphological and experimental data, comparative analyses of the effects of phylogeny, size, and shape, and computational modeling of bone function. Techniques for quantification of three-dimensional jaw and hyoid kinematics across large numbers of cycles have shifted the focus of primate feeding biomechanics from mechanistic studies of small numbers of gape cycles to studies of variation within and between individuals and species. These large-scale studies reveal that the majority of variation in jaw kinematics, in relative timing of jaw muscle activity, and in bone strain patterns is found across gape cycle types and behaviors, not across chews on different foods. This suggests that performance of different kinds of feeding behaviors might be an important determinant of skull design: specifically, external measures of skull morphology might more strongly reflect variation in the ability of the feeding system to generate bite force and transmit it to the bite point, rather than in its ability to resist internal forces (stresses). Variation in feeding system design is structured by three fundamental constraints imposing trade-offs between bite force and gape: the sarcomere structure of skeletal muscle imposes a trade-off between muscle fiber length and muscle force; the primate mandible functions as a third-class lever, so that in combination with the length-tension properties of skeletal muscle, jaw depression and elevation are associated with trade-offs between bite force and gape; and to avoid putting the temporomandibular joint in tension the jaw elevator muscle resultant must pass through the triangle of support defined by the two jaw joints and the bite point. Several decades of in vivo bone strain, morphometric, and modeling studies also suggest that primate crania are impacted by trade-offs with
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 (OR/E and OER), as proxies for bite force. We generated bending and twisting moments (force  moment 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.
The relationship between primate mandibular form and diet has been previously analysed by applying a wide array of techniques and approaches. Nonetheless, most of these studies compared few species and/or infrequently aimed to elucidate function based on an explicit biomechanical framework. In this study, we generated and analysed 31 Finite Element planar models of different primate jaws under different loading scenarios (incisive, canine, premolar and molar bites) to test the hypothesis that there are significant differences in mandibular biomechanical performance due to food categories and/or food hardness. The obtained stress values show that in primates, hard food eaters have stiffer mandibles when compared to those that rely on softer diets. In addition, we find that folivores species have the weakest jaws, whilst omnivores have the strongest mandibles within the order Primates. These results are highly relevant because they show that there is a strong association between mandibular biomechanical performance, mandibular form, food hardness and diet categories and that these associations can be studied using biomechanical techniques rather than focusing solely on morphology. Diet is regarded as one of the main factor underlying the behavioural and ecological differences among living primates, and consequently primate diets have been more exhaustively documented than any other aspect of their behaviour 1. A substantial proportion of physiological and anatomical adaptations have as their fundamental objective the transformation of the ingesta that animals consume. Most primates have been habitually interpreted as mainly adapted to fruit consumption 2 , however it has been also acknowledged that some species occupy specific dietary niches ranging from omnivory to the pure folivory 1. Consequently, primates have been classified into three main diet categories: frugivores, folivores, and omnivores. These broad categories are coherent with much of the structural and nutritional characteristics of the food items observed in primates, and thus frugivores, foli-vores, and omnivores have characteristic features that enable them to process their different diets. Furthermore, some primates are adapted to the consumption of hard items (durophagy; hard-food eaters) whereas others are classified as soft-food consumers 3. The relationship between primate mandibular form and loading during biting has been analysed by numerous studies 4. This interest regarding shape and function in the mandible has not been restricted to primates; in fact, other mammalian clades such as Artiodactyla 5, 6 , Chiroptera 7 , and Carnivora 8, 9 have been studied as well. The close interaction between the mammalian feeding mechanism and the ingesta it processes represents a unique opportunity to study ecomorphological adaptations in extant species and potentially acquire valuable tools for the reconstruction of feeding behaviours in extinct taxa as well. The main function of the mammalian mandible is to transfer the forces generated by the masticatory muscles to the ingesta via the teeth. It has been proposed that mandibular shape is mostly involved in ensuring that the forces are transmitted without being dissipated or causing the mandible to fail structurally 10. Mandibular shape is related to diet through the frequency and magnitude of adductor muscle forces engaged during various oral activities. The greater the forces required to fracture food items (or their protective structures), and the more repeatedly such forces need to be produced (e.g. through repetitive biting), the stronger the mandible has to be to maintain its structural integrity 11. This has been experimentally tested by feeding animal with diets of different Published: xx xx xxxx OPEN
Innovative approaches to the relationship between diet and mandibular morphology in primates.
International Journal of Primatology , 2012
Attempts to establish relationships between mandibular morphology and either traditional dietary categories or geometric and material properties of primate diets have not been particularly successful. Using our conceptual framework of the feeding factors impacting mandibular morphology, we argue that this is because dietary categories and food geometric and material properties affect mandibular morphology only through intervening variables that are currently poorly understood, i.e., feeding behavior, mandibular loading, and stress and strain regimes. Our studies of 3-dimensional jaw kinematics in macaques and capuchins show that, although jaw movement profiles during chewing are affected by food material properties and species-level effects, patterns of jaw movements in these two species are broadly similar. However, because mandibular loading, stress, and strain regimes are determined by interactions between feeding behavior (such as jaw kinematics) and mandibular morphology, it is difficult to say whether these similarities in chewing kinematics also mean similarities in loading, stress, and strain. Comparative analyses of the scaling of daily feeding time and chew cycle duration reveal only weak support for the hypothesis that larger primates chew more than smaller primates. Consideration of these results suggests that better data are needed on the relationship between dietary categories, food material and geometric properties, the amount of time/cycles associated with different feeding behaviors (ingestion, premolar biting, mastication), and mandible stress and strain patterns if we are to understand fully relationships between mandibular morphology and diet in primates.
Vietnamese Journal of …, 2008
Recent studies have identified differences in patterns of food selection, ingestive behavior, dental morphology, and gut physiology among the three major genera of leaf monkey found within Vietnam; Pygathrix, Rhinopithecus, and Trachypithecus. Building on this previous work, Wright et al. (2008) compared chewing rates between Trachypithecus and Pygathrix when masticating leaves of comparable toughness. Trachypithecus was found to chew leaves faster and to have significantly larger lower molars. These findings were argued to support the hypothesis that Trachypithecus species rely more on ingestive behaviors for the processing of leaves, whereas Pygathrix species, with slower chewing rates, smaller molars, and the presence of a "gastric mill" (i.e. presaccus of the stomach) rely more on their digestive tract for the processing of leaves. This study augments the findings of Wright et al. (2008) by comparing four mandibular variables (width and depth of the mandibular symphysis and the mandibular corpus) between Trachypithecus and Pygathrix. These variables are indicative of the ability of the mandible to withstand high or repetitive biting or chewing forces. Measurements were taken on skeletal specimens housed at the
Foraging with finesse: A hard-fruit-eating primate selects the weakest areas as bite sites
American Journal of Physical Anthropology, 2016
Objectives: Fruit husks are rarely uniformly hard, varying in penetrability via sulci and changes in thickness. We tested whether a hard-food specialist primate i) bites randomly on food fruit husk surfaces to access seeds, or ii) selects areas most easily penetrated by canines. We consider this would occur so as to minimize deployed mechanical force, energetic expenditure and risk of dental breakage when feeding. Methods: A sulcus is the natural line of weakness where a dehiscent fruit breaks open. Using fruits dentally opened for seeds by golden-back uacaris (Cacajao ouakary) we: 1) analysed bite mark distribution on surface of four fruits types (hard-with-sulcus, soft-with-sulcus, hard-no-sulcus, soft-no-sulcus); 2) quantified the force needed to penetrate hard and soft fruits at sulci and elsewhere on fruit surface; 3) measured fruit wall thickness and correlated it with bite-mark distribution in all four categories of fruit. Results: 1) Bite marks were distributed at random only on surfaces of soft fruits. For other fruits types, bite locations were concentrated at the thinnest areas of husk, either over the entire surface (non-sulcate fruits), or at sulci (sulcate fruits). 2) For hard-husked fruits, areas where uacaris concentrated their bites were significantly easier to penetrate than those where they did not. Conclusions: This hard-fruit feeding specialist primate is not biting at random on the surface of diet fruits. To access seeds they are focusing on those areas requiring less force to penetrate. This may be to save energy, to minimize the risk of breaking teeth used in food processing, or a combination of both. The study shows, for the first time, the subtlety by which these powerfully-jawed animals process their diet items.