Evolution of muscle activity patterns driving motions of the jaw and hyoid during chewing in Gnathostomes

Although chewing has been suggested to be a basal gnathostome trait retained in most major vertebrate lineages, it has not been studied broadly and comparatively across vertebrates. To redress this imbalance, we recorded EMG from muscles powering anteroposterior movement of the hyoid, and dorsoventral movement of the mandibular jaw during chewing. We compared muscle activity patterns (MAP) during chewing in jawed vertebrate taxa belonging to unrelated groups of basal bony fishes and artiodactyl mammals. Our aim was to outline the evolution of coordination in MAP. Comparisons of activity in muscles of the jaw and hyoid that power chewing in closely related artiodactyls using cross-correlation analyses identified reorganizations of jaw and hyoid MAP between herbivores and omnivores. EMG data from basal bony fishes revealed a tighter coordination of jaw and hyoid MAP during chewing than seen in artiodactyls. Across this broad phylogenetic range, there have been major structural reorganizations, including a reduction of the bony hyoid suspension, which is robust in fishes, to the acquisition in a mammalian ancestor of a muscle sling suspending the hyoid. These changes appear to be reflected in a shift in chewing MAP that occurred in an unidentified anamniote stem-lineage. This shift matches observations that, when compared with fishes, the pattern of hyoid motion in tetrapods is reversed and also time-shifted relative to the pattern of jaw movement.     

Lectin-binding patterns in epithelial lining of jaw cysts

Lectin-binding patterns were examined in epithelial walls of 65 jaw cysts (30 post-operative maxillary cysts: POMCs, 20 radicular and 15 follicular cysts), and characteristic lectin staining for each kind of jaw cysts is presented. Between squamous and columnar epithelia, the staining intensity of WGA, Con A and UEA-I was not different, but SBA bound more remarkably to squamous than to columnar epithelia. In both epithelia the outer layers did react more strongly with the lectins examined. Concerning odontogenic cysts, the lectin-binding affinities of outer and intermediate layer cells were nearly the same in both follicular and radicular cysts. Basal cells of radicular cyst walls were however, more markedly positive for lectin binding than of follicular cysts. Furthermore, basal cells of keratinized (RKSE 60 keratin-positive) epithelium were inferior to those of non-keratinized linings in the bindings. Lectin-binding patterns of metaplastic squamose epithelia of POMCs which were positive for RGE53-keratin (principally columnar epithelium-specific keratin) were similar to originally squamous linings of odontogenic cysts. Columnar linings of unusual radicular cysts were positively stained with SBA. By these results, lectin-binding sugar residues of the epithelium seem to be related to the epithelial morphology.     

Evolution of the vertebrate jaw from developmental perspectives

Attainment of the biting jaw is regarded as one of the major novelties in the early history of vertebrates. Based on a comparison between lamprey and gnathostome embryos, evolutionary developmental studies have tried to explain this novelty as changes in the developmental patterning of the mandibular arch, the rostralmost pharyngeal arch, at the molecular and cellular levels. On the other hand, classical theories in the field of comparative morphology assumed the involvement of hypothetical premandibular arch(es) that ancestral animals would have possessed rostral to the mandibular arch, in the transition from agnathan to gnathostome states. These theories are highly biased toward the segmental scheme of the vertebrate head, and the concept of premandibular “arches” is no longer accepted by the current understanding. Instead, the premandibular domain has now become of interest in the understanding of cranial development, especially in its rostral part. As newer theories that consider involvement of the premandibular domain, the neoclassical and heterotopy theories are here compared from evolutionary developmental perspectives, in conjunction with the development of nasal and hypophyseal placodes, in the context of the evolutionary acquisition of the jaw. Given recent advances in understanding of the lamprey development, evolution of the Dlx code is also discussed together with the evolutionary scenario of jaw acquisition.     

Curvature of the forelimb bones of anthropoid primates: Overall allometric patterns and specializations in suspensory species

It has previously been reported that brachiating primates, particularly gibbons, are characterized by distinctively straight forelimb long bones, yet no hypotheses have been proposed to explain why straight limb bones may be adaptive to suspensory locomotion. This study explores quantitatively the curvature of the long bones in 13 species of anthropoid primates and analyzes the functional consequences of curvature in biomechanical terms. These analyses demonstrate that, whereas the humeri of gibbons and spider monkeys are functionally less curved than those of other taxa, the ulnae of brachiators are neither more nor less curved than those of other anthropoids, and the gibbon radius is far more curved than would be predicted from body size alone. The humerus is likely significantly less curved in brachiators because of its torsion-dominated loading regime and the greatly increased stress magnitude developed in torsionally loaded curved beams. The large curvature of the radius is localized in the region of attachment of the supinator muscle. Analysis presented here of muscle mass allometry in catarrhines demonstrates that gibbons are characterized by an extremely massive supinator, and the large radial curvature is therefore most likely due to forearm muscle mechanics. This study also demonstrates that the overall pattern of limb bone curvature for anthropoids is distinct from the pattern reported for mammals as a whole. This distinctive scaling relationship may be related to the increased length of the limb bones of primates in comparison to other mammals.     

Differences in loading of the temporomandibular joint during opening and closing of the jaw

Kinematics of the human masticatory system during opening and closing of the jaw have been reported widely. Evidence has been provided that the opening and closing movement of the jaw differ from one another. However, different approaches of movement registration yield divergent expectations with regard to a difference in loading of the temporomandibular joint between these movements. Because of these diverging expectations, it was hypothesized that joint loading is equal during opening and closing. This hypothesis was tested by predicting loading of the temporomandibular joint during an unloaded opening and closing movement of the jaw by means of a three-dimensional biomechanical model of the human masticatory system. Model predictions showed that the joint reaction forces were markedly higher during opening than during closing. The predicted opening trace of the centre of the mandibular condyle was located cranially of the closing trace, with a maximum difference between the traces of 0.45 mm. The hypothesis, postulating similarity of joint loading during unloaded opening and closing of the jaw, therefore, was rejected. Sensitivity analysis showed that the reported differences were not affected in a qualitative sense by muscular activation levels, the thickness of the cartilaginous layers within the temporomandibular joint or the gross morphology of the model. Our predictions indicate that the TMJ is loaded more heavily during unloaded jaw opening than during unloaded jaw closing.     

The effect of loading on kinematic and kinetic variables during the midthigh clean pull

The ability to develop high levels of muscular power is considered a fundamental component for many different sporting activities; however, the load that elicits peak power still remains controversial. The primary aim of this study was to determine at which load peak power output occurs during the midthigh clean pull. Sixteen participants (age 21.5 ± 2.4 years; height 173.86 ± 7.98 cm; body mass 70.85 ± 11.67 kg) performed midthigh clean pulls at intensities of 40, 60, 80, 100, 120, and 140% of 1 repetition maximum (1RM) power clean in a randomized and balanced order using a force plate and linear position transducer to assess velocity, displacement, peak power, peak force (Fz), impulse, and rate of force development (RFD). Significantly greater Fz occurred at a load of 140% (2,778.65 ± 151.58 N, p < 0.001), impulse within 100, 200, and 300 milliseconds at a load of 140% 1RM (196.85 ± 76.56, 415.75 ± 157.56, and 647.86 ± 252.43 N·s, p < 0.023, respectively), RFD at a load of 120% (26,224.23 ± 2,461.61 N·s, p = 0.004), whereas peak velocity (1.693 ± 0.042 m·s, p < 0.001) and peak power (3,712.82 ± 254.38 W, p < 0.001) occurred at 40% 1RM. Greatest total impulse (1,129.86 ± 534.86 N·s) was achieved at 140% 1RM, which was significantly greater (p < 0.03) than at all loads except the 120% 1RM condition. Results indicate that increased loading results in significant (p < 0.001) decreases in peak power and peak velocity during the midthigh clean pull. Moreover, if maximizing force production is the goal, then training at a higher load may be advantageous, with peak Fz occurring at 140% 1RM.     

Dental microwear texture and anthropoid diets

Dental microwear has long been used as evidence concerning the diets of extinct species. Here, we present a comparative baseline series of dental microwear textures for a sample of 21 anthropoid primate species displaying interspecific and intraspecific dietary variability. Four dental microwear texture variables (complexity, anisotropy, textural fill volume, and heterogeneity) were computed based on scale-sensitive fractal analysis and high-resolution three-dimensional renderings of microwear surfaces collected using a white-light confocal profiler. The purpose of this analysis was to assess the extent to which these variables reflect variation in diet. Significant contrasts between species with diets known to include foods with differing material properties are clearly evident for all four microwear texture variables. In particular, species that consume more tough foods, such as leaves, tended to have high levels of anisotropy and low texture complexity. The converse was true for species including hard and brittle items in their diets either as staples or as fallback foods. These results reaffirm the utility of dental microwear texture analysis as an important tool in making dietary inferences based on fossil primate samples.     

Two patterns of differentiation in the jaw musculature of teleostean fishes

In its most generalized configuration among modern teleosts the M. adductor mandibulae comprises a single, almost continuous mass of musculature extending from the cheek to the inner surface of the mandible. In more advanced teleosts this muscle is usually divided into sections. Two basically different pathways of differentiation in the cheek part of the adductor mandibulae are dealt with here. One is that in the ostariophysine fishes. The other is represented in at least the great majority of acanthopterygians. Only certain of the differentiated sections are homologous in these two large groups of fishes.     

A model relating patterns of human jaw movement to biomechanical constraints

After testing the effects of the ways in which several different ligaments and bony constraints would influence movements of the human mandible in three dimensions, a mathematical model based on constraints due to the articular eminences, temporomandibular ligaments and sphenomandibular ligaments has been constructed. The effects of these constraints on jaw movements during opening and lateral movements are analysed. The model predicts the observed translation of the human condyle during jaw opening and Bennett shift during lateral jaw movements. The model is refined to account for observed irregular movements of the condyle during opening and to predict a locus for the instantaneous centre of rotation. The model can also be used to predict the new position taken up by any point on the mandible after the jaw has been opened and/or moved laterally a given amount.     

Evolution and development of the mammalian jaw joint: Making a novel structure

A jaw joint between the squamosal and dentary is a defining feature of mammals and is referred to as the temporomandibular joint (TMJ) in humans. Driven by changes in dentition and jaw musculature, this new joint evolved early in the mammalian ancestral lineage and permitted the transference of the ancestral jaw joint into the middle ear. The fossil record demonstrates the steps in the cynodont lineage that led to the acquisition of the TMJ, including the expansion of the dentary bone, formation of the coronoid process, and initial contact between the dentary and squamosal. From a developmental perspective, the components of the TMJ form through tissue interactions of muscle and skeletal elements, as well as through interaction between the jaw and the cranial base, with the signals involved in these interactions being both biomechanical and biochemical. In this review, we discuss the development of the TMJ in an evolutionary context. We describe the evolution of the TMJ in the fossil record and the development of the TMJ in embryonic development. We address the formation of key elements of the TMJ and how knowledge from developmental biology can inform our understanding of TMJ evolution.     

Wrist loading patterns during pommel horse exercises

Gymnastics is a sport which involves substantial periods of upper extremity support as well as frequent impacts to the wrist. Not surprisingly, wrist pain is a common finding in gymnasts. Of all events, the pommel horse is the most painful. In order to study the forces of wrist impact, a standard pommel horse was instrumented with a specially designed load cell to record the resultant force of the hand on the pommel during a series of basic skills performed by a group of seventeen elite male gymnasts. The highest mean peak forces were recorded during the front scissors and flair exercises (1.5 BW) with peaks of up to 2.0 BW for some gymnasts. The mean peak force for hip circles at the center or end of the horse was 1.1 BW. The mean overall loading rate (initial contact to first loading peak) ranged from 5.2 BWs-1 (hip circles) to 10.6 BW s-1 (flairs). However, many recordings displayed localized initial loading spikes which occurred during 'hard' landings on the pommel. When front scissors were performed in an aggressive manner, the initial loading spikes averaged 1.0 BW in magnitude (maximum 1.8 BW) with an average rise time of 8.2 ms; calculated localized loading rates averaged 129 BW s-1 (maximum 219 BW s-1). These loading parameters are comparable to those encountered at heel strike during running. These impact forces and loading rates are remarkably high for an upper extremity joint not normally exposed to weight-bearing loads, and may contribute to the pathogenesis of wrist injuries in gymnastics.     

Evolution of marine invertebrate reproductive patterns

A simple model of the evolution of reproductive patterns in marine benthic invertebrates is presented. The aim is to discuss the dichotomous distribution of forms into those which produce a large number of small eggs with planktotrophic development, and those which produce a small number of large eggs with direct or lecithotrophic development. The fecundity of adult individuals is assumed to be inversely proportional to egg size, and the mortality of planktonic larvae is assumed to be density independent and size dependent. The growth of planktonic larvae is assumed to be sigmoid with metamorphosis occurring at a given size. The model concludes that there are at most two evolutionarily stable egg sizes. Depending on larval growth rate and death rate, the metamorphosis size, a smaller egg size, or both may be evolutionarily stable. The predictions of the model are compared to patterns observed in nature. Illustrative data are supplied mainly from prosobranch molluscs.     

Evolution of jaw depression mechanics in aquatic vertebrates: insights from Ghondrichthyes

The widely accepted phylogenctic position of Chondrichthyes as the sister group to all other living gnathostomes makes biomechanical analyses of this group of special significance for estimates of skull function in early jawed vertebrates. We review key findings of recent experimental research on the feeding mechanisms of living elasmobranchs with respect to our understanding of jaw depression mechanisms in gnathostome vertebrates. We introduce the possibility that the ancestral jaw depression mechanism in gnathostomes was mediated by the coracomandibularis muscle and that for hyoid depression by the coracohyoideus muscle, as in modern Chondrichthyes and possibly placoderms. This mechanism of jaw depression appears to have been replaced by the sternohyoideus (homologous to the coracohyoideus) coupling in Osteichthycs following the split of this lineage from Chondrichthyes. Concurrent with the replacement of the branchiomandibularis (homologous to the coracomandibularis) coupling by the sternohyoideus coupling as the dominant mechanism of jaw depression in Osteichthyes was the fusion and shift in attachment of the intcrhyoideus and intermandibularis muscles (producing the protractor hyoideus muscle, mistakenly refereed to as the geniohyoideus), which resulted in a more diversified role of the sternohyoideus coupling in Osteichthyes. The coracohyoideus coupling appears to have been already present in vertebrates where it functioned in hyoid depression, as in modern Chondrichthyes, before it acquired the additional role of jaw depression in Osteichthyes.     

Plate tectonics and the problem of anthropoid origins

Using plate tectonic theory, geologic and geophysical determinants of South Atlantic opening are assessed during the Cretaceous through the Oligocene (approximately 135–25 m.y.B.P.). This is done to evalute the feasibility of statements on paleontologic and neontologic distributional data that relate to African and South American separation as the South Atlantic was created. In particular, the question of anthropoid origins is examined in light of plate tectonic theory, and the idea that monophyly of the anthropoid grade is supported by continental drift is refuted. When geological and geophysical evidence is examined in detail, the occurrence of Tertiary transfer of primates between Africa and South America is improbable. Thus one must look to either North America or Middle America for the ancestors of the platyrrhines, and to Eurasia for the ancestors of the catarrhines. The problem of whether those ancestors were prosimians or anthropoids is not dealt with, because the question of whether the Platyrrhini and the Catarrhini are independently evolved from prosimian ancestors (anthropoid diphyly) or are evolved from ancestors that were already of an anthropoid level of structural organization (anthropoid monophyly) can only be resolved on biological grounds and at a level of analysis that allows one to distinguish between analogies developed in parallel, homologies caused by symple-siomorphy, and homologies caused by synapomorphy.     

Polymorphic aspects of male anthropoid canines

Interspecific variation in the architecture of male anthropoid maxillary canines is documented. Extant taxa are polymorphic, and most can be sorted into two major groupings based on quantitative measures of shape, distal edge sharpness, and interspecific changes in their linear dimensions (projection, mesiodistal length, and buccolingual breadth) relative to each other and to body mass (scaling). One group includes the great apes and ceboids; the other includes cercopithecoids and hylobatids. Statistically significant differences between these groups were found for canine shape, for trajectories of regressions for canine projection on canine length and canine breadth, and for canine projection and canine breadth relative to body mass. The data indicate that explantations of canine variation in male anthropoids must include a mechanical interpretation of form in addition to assessments of habitus, heritage, and body mass.     

Incisor microwear of Sumatran anthropoid primates

Several studies have suggested that incisor microwear reflects diet and feeding adaptations of anthropoids. However, such studies have been largely qualitative, and interpretations have relied on anecdotal references to diet and tooth use reported in the socioecology literature. The current study relates incisor microwear in four anthropoid primates to specific ingestive behaviors and food types. Central incisor casts of wild-shot museum specimens of Hylobates lar, Macaca fascicularis, Pongo pygmaeus, and Presbytis thomasi were examined by scanning electron microscopy, and analyzed using a semiautomated image analysis procedure. Microwear patterns were used to generate predictions regarding diet and anterior tooth use. These predictions were evaluated using data collected during a 1 year study of feeding behavior of these same taxa in the wild (Ungar, 1992, 1994a, b). Results suggest that (1) enamel prism relief is associated with the effectiveness of etching reagents in foods, (2) dental calculus buildup results from a lack of incisor use and perhaps the ingestion of sugar-rich foods, (3) striation density varies with degree of anterior tooth use in the ingestion of abrasive food items, (4) striation breadth is proposed to relate to the ratio of exogenous grit to phytoliths consumed; and (5) preferred striation orientation indicates the direction that food items are pulled across the incisors during ingestion. It is concluded that incisor microwear studies can contribute to the understanding of diets and feeding behaviors of extinct primates. © 1994 Wiley-Liss, Inc.     

Evolution of novel jaw joints promote trophic diversity in coral reef fishes

We investigated the functional morphology and ecology of biting among the squamipinnes, an assemblage of nine successful and distinctive reef fish families. We demonstrate that an intramandibular joint (IMJ) may have evolved at least three and possibly five times in this assemblage and discuss the impact of this recurring innovation in facilitating prey-capture by biting. Using character mapping on a supertree for the squamipinnes, we reveal up to seven gains or losses of intramandibular flexion, all associated with trophic transitions between free-living and attached prey utilization. IMJs are basal in six of the studied families whereas the origin of intramandibular flexion in the Chaetodontidae (butterflyfishes) coincides with a transition from ram-suction feeding to benthic coral feeding, with flexion magnitude reaching its peak (49 ± 2.7°) in the coral scraping subgenus Citharoedus . Although IMJs generally function to augment vertical gape expansion during biting behaviours to remove small invertebrates, algae or coral from the reef, the functional ecology of IMJs in the Pomacanthidae (angelfishes) stands in contrast. Pomacanthid IMJs exhibit over 35° of flexion, permitting gape closure when the jaws are fully protruded. We demonstrate the widespread IMJ occurrence among extant biters to result from a complex convergent evolutionary history, indicating that the IMJ is a major functional innovation that enhances biting strategies in several prominent reef fish groups.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 545–555.     

Weightlifting performance is related to kinematic and kinetic patterns of the hip and knee joints

The purpose of this study was to investigate the correlations between biomechanical outcome measures and weightlifting performance. Joint kinematics and kinetics of the hip, knee, and ankle were calculated while 10 subjects performed a clean at 85% of 1 repetition maximum (1RM). Kinematic and kinetic time-series patterns were extracted with principal components analysis. Discrete scores for each time-series pattern were calculated and used to determine how each pattern was related to body mass-normalized 1RM. Two hip kinematic and 2 knee kinetic patterns were significantly correlated with relative 1RM. The kinematic patterns captured hip and trunk motions during the first pull and hip joint motion during the movement transition between the first and second pulls. The first kinetic pattern captured a peak in the knee extension moment during the second pull. The second kinetic pattern captured a spatiotemporal shift in the timing and amplitude of the peak knee extension moment. The kinematic results suggest that greater lift mass was associated with steady trunk position during the first pull and less hip extension motion during the second-knee bend transition. Further, the kinetic results suggest that greater lift mass was associated with a smaller knee extensor moments during the first pull, but greater knee extension moments during the second pull, and an earlier temporal transition between knee flexion-extension moments at the beginning of the second pull. Collectively, these results highlight the importance of controlled trunk and hip motions during the first pull and rapid employment of the knee extensor muscles during the second pull in relation to weightlifting performance.