Mechanisms of the jaws of some atheriniform fish

The Atheriniformes is an order of teleost fish which consists of the Atherinoidei (sand smelts etc.), Cyprinodontoidei (tooth-carps) and Exocoetoidei (halfbeaks etc.). Some of its members have protrusible upper jaws and some do not. Photographs have been taken of two species of Cyprinodontoidei feeding, to discover how they use their jaws, which are protrusible. The anatomy and mechanisms of the jaws of these and of various other Atheriniformes have been studied. The terminology of the kinematics of machines is used in a general discussion of the mechanisms of teleost jaws. Anatomical similarities between the jaws of Acanthopterygii, Cyprinoidei and Atheriniformes are noted and discussed.     

Mechanisms of the jaws of some atheriniform fish

The Atheriniformes is an order of teleost fish which consists of the Atherinoidei (sand smelts etc.), Cyprinodontoidei (tooth-carps) and Exocoetoidei (halfbeaks etc.). Some of its members have protrusible upper jaws and some do not. Photographs have been taken of two species of Cyprinodontoidei feeding, to discover how they use their jaws, which are protrusible. The anatomy and mechanisms of the jaws of these and of various other Atheriniformes have been studied. The terminology of the kinematics of machines is used in a general discussion of the mechanisms of teleost jaws. Anatomical similarities between the jaws of Acanthopterygii, Cyprinoidei and Atheriniformes are noted and discussed.     

Making up the numbers: The molecular control of mammalian dental formula

Teeth develop in the mammalian embryo via a series of interactions between odontogenic epithelium and neural crest-derived ectomesenchyme of the early jaw primordia. The molecular interactions required to generate a tooth are mediated by families of signalling molecules, which often act reiteratively in both a temporal and spatial manner. Whilst considerable information is now available on how these molecules interact to produce an individual tooth, much less is known about the processes that control overall tooth number within the dentition. However, a number of mouse models are now starting to provide some insight into the mechanisms that achieve this. In particular, co-ordinated restriction of signalling molecule activity is important in ensuring appropriate tooth number and there are different requirements for this suppression in epithelial and mesenchymal tissues, both along different axes of individual jaws and between the jaws themselves. There are a number of fundamental mechanisms that facilitate supernumerary tooth formation in these mice. A key process appears to be the early death of vestigial tooth primordia present in the embryo, achieved through the suppression of Shh signalling within these early teeth. However, restriction of WNT signalling is also important in controlling tooth number, with increased transduction being capable of generating multiple tooth buds from the oral epithelium or existing teeth themselves, in both embryonic and adult tissues. Indeed, uncontrolled activity of this pathway can lead to the formation of odontogenic tumours containing multiple odontogenic tissues and poorly formed teeth. Finally, disrupted patterning along the buccal–lingual aspect of the jaws can produce extra teeth directly from the oral epithelium in a duplicated row. Together, all of these findings have relevance for human populations, where supernumerary teeth are seen in association with both the primary and permanent dentitions. Moreover, they are also providing insight into how successional teeth form in both embryonic and post-natal tissues of the jaws.     

An Ancient Gene Network Is Co-opted for Teeth on Old and New Jaws

Vertebrate dentitions originated in the posterior pharynx of jawless fishes more than half a billion years ago. As gnathostomes (jawed vertebrates) evolved, teeth developed on oral jaws and helped to establish the dominance of this lineage on land and in the sea. The advent of oral jaws was facilitated, in part, by absence of hox gene expression in the first, most anterior, pharyngeal arch. Much later in evolutionary time, teleost fishes evolved a novel toothed jaw in the pharynx, the location of the first vertebrate teeth. To examine the evolutionary modularity of dentitions, we asked whether oral and pharyngeal teeth develop using common or independent gene regulatory pathways. First, we showed that tooth number is correlated on oral and pharyngeal jaws across species of cichlid fishes from Lake Malawi (East Africa), suggestive of common regulatory mechanisms for tooth initiation. Surprisingly, we found that cichlid pharyngeal dentitions develop in a region of dense hox gene expression. Thus, regulation of tooth number is conserved, despite distinct developmental environments of oral and pharyngeal jaws; pharyngeal jaws occupy hox-positive, endodermal sites, and oral jaws develop in hox-negative regions with ectodermal cell contributions. Next, we studied the expression of a dental gene network for tooth initiation, most genes of which are similarly deployed across the two disparate jaw sites. This collection of genes includes members of the ectodysplasin pathway, eda and edar, expressed identically during the patterning of oral and pharyngeal teeth. Taken together, these data suggest that pharyngeal teeth of jawless vertebrates utilized an ancient gene network before the origin of oral jaws, oral teeth, and ectodermal appendages. The first vertebrate dentition likely appeared in a hox-positive, endodermal environment and expressed a genetic program including ectodysplasin pathway genes. This ancient regulatory circuit was co-opted and modified for teeth in oral jaws of the first jawed vertebrate, and subsequently deployed as jaws enveloped teeth on novel pharyngeal jaws. Our data highlight an amazing modularity of jaws and teeth as they coevolved during the history of vertebrates. We exploit this diversity to infer a core dental gene network, common to the first tooth and all of its descendants.     

The oldest Gondwanan cephalopod mandibles (Hangenberg Black Shale,Late Devonian) and the mid‐Palaeozoic rise of jaws

It is widely accepted that the effects of global sea‐level changes at the transition from the Devonian to the Carboniferous are recorded in deposits on the shelf of northern Gondwana. These latest Devonian strata had been thought to be poor in fossils due to the Hangenberg mass extinction. In the Ma'der (eastern Anti‐Atlas), however, the Hangenberg Black Shale claystones (latest Famennian) are rich in exceptionally preserved fossils displaying the remains of non‐mineralized structures. The diversity in animal species of these strata is, however, low. Remarkably, the organic‐rich claystones have yielded abundant remains of Ammonoidea preserved with their jaws, both in situ and isolated. This is important because previously, the jaws of only one of the main Devonian ammonoid clades had been found (Frasnian Gephuroceratina). Here, we describe four types of jaws of which two could be assigned confidently to the Order Clymeniida and to the Suborder Tornoceratina. These findings imply that chitinous normal‐type jaws were likely to have already been present at the origin of the whole clade Ammonoidea, i.e. in the early Emsian (or earlier). Vertebrate jaws evolved prior to the Early Devonian origin of ammonoids. The temporal succession of evolutionary events suggests that it could have been the indirect positive selection pressure towards strong (and thus preservable) jaws since defensive structures of potential prey animals would otherwise have made them inaccessible to jawless predators in the course of the mid‐Palaeozoic marine revolution. In this respect, our findings reflect the macroecological changes that occurred in the Devonian. [Correction added on 28 July 2016 after first online publication: In the Abstract, the sentence “Vertebrate jaws probably … in the Early Devonian” was amended]     

Roentgencephalometric study of cranial interrelations

Lateral X-ray films of the skull obtained in 50 normal adult males were used for studies of correlations between 26 characteristics of the size, shape, and position of the face and nine characteristics of the neurocranium in all mutual combinations. The results disclosed that the relations between individual cranial components were regulated by certain principles. The correlations between size dimensions were mostly slight; a closer relationship showed some characteristics of the shape and position. The most important variable exerting an effect on the configuration of the skull as a whole represented the angle of the cranial base which produced the rotation of the neurocranium and the face and thus acted on a series of other correlations. Of some importance as well was the length of the mandibular ramus acting on the shape and position of the lower jaw and on the vertical maxillomandibular relations. The close relationship between the anteroposterior position of both jaws was due to compensation mechanisms rather than to the identical size of both jaws. On normalization of the disturbed saggital jaw relations, the dentoalveolar components of both jaws as well as the subalveolar component of the mandible participated equally. In vertical direction the lower face showed a certain developmental independence. The discussed interrelations formed the basis for studies of the mechanisms regulating the intracranial development and the changes occurring in various anomalies, as well as for understanding the compensation and adaptation abilities of individual cranial components.     

Rhyncholites and conchorhynchs as calcified jaw elements in some late Cretaceous ammonites

Conspicuous calcareous coverings are present in the anterior region of 17 fossil jaws from late Cretaceous rocks of Hokkaido (Japan) and Sakhalin (U.S.S.R.). The jaws were preserved in calcareous nodules either in situ in body chambers of ammonites or in close association with identifiable ammonite conch remains. From the morphologic similarity between in situ and isolated jaws, they may be attributed to Tetragonites glabrus, Gaudryceras tenuiliratum, G. denseplicatum, G. sp., and Neophylloceras subramosum. The jaw apparatus of these species is composed of two three-dimensional black walls of carbonate apatite, which might be a diagenetic replacement of chitinous material. The calcareous coverings in both upper and lower jaws closely resemble those of upper (rhyncholite) and lower (conchorhynch) jaws of modern Nautilus as well as rhyncholite and conchorhynch fossils in their gross morphology, microstructure, and chemical composition. Calcified remains of cephalopod jaws known as rhyncholites and conchorhynchs have been reported from late Paleozoic to Recent. The present discovery of ammonoid rhyncholites and conchorhynchs suggests that at least some previously known late Paleozoic and Mesozoic counterparts belong to the Ammonoidea. The essential similarity of jaw elements of some Late Cretaceous ammonites and modern Nautilus gives reliable information on the feeding habits of the former. The sharp and thick ammonoid rhyncholites and conchorhynchs may have had a special function for cutting up food, similar to those of Nautilus.     

Structure and function of the horn shark (Heterodontus francisci) cranium through ontogeny: development of a hard prey specialist

The horn sharks (Heterodontidae: Chondrichthyes) represent one of four independent evolutions of durophagy in the cartilaginous fishes. We used high-resolution computed tomography (CT scanning) to visualize and quantify the mineralized tissue of an ontogenetic series of horn sharks. CT scanning of neonatal through adult California horn sharks (Heterodontus francisci) confirmed that this technique is effective for examining mineralized tissue in even small (<10 mm) specimens. The jaw joint is among the first areas to become mineralized and is the most heavily mineralized area in the cranium of a neonatal horn shark. The hyoid is also well mineralized, although the poorly mineralized molariform teeth indicate that the neonatal animal may be a suction feeder on softer prey. The symphysis of the jaws never mineralizes, in sharp contrast to the condition in the hard prey-crushing stingrays. Digitally reslicing the CT scans along the jaws allowed measurement of the second moment of area (Ina). Assuming that the jaws are made of the same material at all ages, Ina is an indicator of the flexural stiffness of the jaws. In all sizes of shark the lower jaws were stiffer than the upper and the stiffness increased in the area of the molariform teeth. The central region of the jaws, where the rami meet, support cuspidate grasping teeth and has the lowest Ina. The spotted eagle ray (Aetobatus narinari), a hard prey-crushing stingray, shows a different pattern of flexural stiffness, with the peak at the central part of the jaws where the prey is reduced between flattened tooth plates. Although the eagle ray jaws have a higher Ina than the horn shark, they are also far more heavily mineralized. When the relative amounts of mineralization are taken into account, horn sharks do better with what mineral they have than does the eagle ray. With a tight jaw joint and loose mandibular symphysis, as well as nearly opposite patterns of stiffness in the jaws, it is clear that two of the clades of hard prey specialists use very different methods for cracking the hard prey problem.     

Mechanics of biting in great white and sandtiger sharks

Although a strong correlation between jaw mechanics and prey selection has been demonstrated in bony fishes (Osteichthyes), how jaw mechanics influence feeding performance in cartilaginous fishes (Chondrichthyes) remains unknown. Hence, tooth shape has been regarded as a primary predictor of feeding behavior in sharks. Here we apply Finite Element Analysis (FEA) to examine form and function in the jaws of two threatened shark species, the great white (Carcharodon carcharias) and the sandtiger (Carcharias taurus). These species possess characteristic tooth shapes believed to reflect dietary preferences. We show that the jaws of sandtigers and great whites are adapted for rapid closure and generation of maximum bite force, respectively, and that these functional differences are consistent with diet and dentition. Our results suggest that in both taxa, insertion of jaw adductor muscles on a central tendon functions to straighten and sustain muscle fibers to nearly orthogonal insertion angles as the mouth opens. We argue that this jaw muscle arrangement allows high bite forces to be maintained across a wider range of gape angles than observed in mammalian models. Finally, our data suggest that the jaws of sub-adult great whites are mechanically vulnerable when handling large prey. In addition to ontogenetic changes in dentition, further mineralization of the jaws may be required to effectively feed on marine mammals. Our study is the first comparative FEA of the jaws for any fish species. Results highlight the potential of FEA for testing previously intractable questions regarding feeding mechanisms in sharks and other vertebrates.     

Functional morphology of durophagy in black carp,Mylopharyngodon piceus

The black carp, Mylopharyngodon piceus (Osteichthyes: Cyprinidae), crushes its snail and other molluscan prey with robust pharyngeal jaws and strong bite forces. Using gross morphology, histological sectioning, and X‐ray reconstruction of moving morphology (XROMM), we investigated structural, behavioral, and mechanical aspects of pharyngeal jaw function in black carp. Strut‐like trabeculae in their pharyngeal jaws support large, molariform teeth. The teeth occlude with a hypertrophied basioccipital process that is also reinforced with stout trabeculae. A keratinous chewing pad is firmly connected to the basioccipital process by a series of small bony projections from the base of the pedestal. The pharyngeal jaws have no bony articulations with the skull, and their position is controlled by five paired muscles and one unpaired median muscle. Black carp can crush large molluscs, so we used XROMM to compare pharyngeal jaw postures as fish crushed ceramic tubes of increasing sizes. We found that black carp increase pharyngeal jaw gape primarily by ventral translation of the jaws, with ventral rotation and lateral flaring of the jaws also increasing the space available to accommodate large prey items. A stout, robust ligament connects left and right jaws together firmly, but allows some rotation of the jaws relative to each other. Contrasting with the pharyngeal jaw mechanism of durophagous perciforms with fused left and right lower pharyngeal jaws, we hypothesize that this ligamentous connection may serve to decouple tensile and compressive forces, with the tensile forces borne by the ligament and the compressive forces transferred to the prey. J. Morphol. 276:1422–1432, 2015. © 2015 Wiley Periodicals, Inc.     

The genetic architecture of novel trophic specialists: larger effect sizes are associated with exceptional oral jaw diversification in a pupfish adaptive radiation

The genetic architecture of adaptation is fundamental to understanding the mechanisms and constraints governing diversification. However, most case studies focus on loss of complex traits or parallel speciation in similar environments. It is still unclear how the genetic architecture of these local adaptive processes compares to the architecture of evolutionary transitions contributing to morphological and ecological novelty. Here, we identify quantitative trait loci (QTL) between two trophic specialists in an excellent case study for examining the origins of ecological novelty: a sympatric radiation of pupfishes endemic to San Salvador Island, Bahamas, containing a large‐jawed scale‐eater and a short‐jawed molluscivore with a skeletal nasal protrusion. These specialized niches and trophic traits are unique among over 2000 related species. Measurements of the fitness landscape on San Salvador demonstrate multiple fitness peaks and a larger fitness valley isolating the scale‐eater from the putative ancestral intermediate phenotype of the generalist, suggesting that more large‐effect QTL should contribute to its unique phenotype. We evaluated this prediction using an F2 intercross between these specialists. We present the first linkage map for pupfishes and detect significant QTL for sex and eight skeletal traits. Large‐effect QTL contributed more to enlarged scale‐eater jaws than the molluscivore nasal protrusion, consistent with predictions from the adaptive landscape. The microevolutionary genetic architecture of large‐effect QTL for oral jaws parallels the exceptional diversification rates of oral jaws within the San Salvador radiation observed over macroevolutionary timescales and may have facilitated exceptional trophic novelty in this system.     

Melanin and Glycera jaws: emerging dark side of a robust biocomposite structure

Defining the design principles guiding the fabrication of superior biocomposite structures from an assemblage of ordinary molecules is a key goal of biomimetics. Considering their low degree of mineralization, Glycera jaws have been shown to be extraordinarily resistant to abrasion based on the metric hardness3/Young's modulus2. The jaws also exhibit an impressive chemical inertness withstanding boiling concentrated hydrochloric acid as well as boiling concentrated sodium hydroxide. A major organic component largely responsible for the chemical inertness of the jaws has been characterized using a spectrophotometric assay for melanin content, 13C solid state nuclear magnetic resonance, IR spectroscopy, and laser desorption ionization-time of flight mass spectrometry and is identified here as a melanin-like network. Although melanin is widely distributed as a pigment in tissues and other structural biomaterials, to our knowledge, Glycera jaws represent the first known integument to exploit melanin as a cohesive load- and shape-bearing material.     

Research in Mammalian Mastication

Ongoing research efforts in mammalian mastication have definedseveral broad areas of mutual interest to workers in the discipline.They are (1) interrelationships between masticatory movements,(2) actions of the masticatory muscles, (3) comparisons betweenmasticatory structures and functions, (4) developmental aspects,(5) comparisons between limbs and jaws, and (6) neurophysiologicconsiderations. The roles (potential and actual) of masticatorycentral pattern generators, cerebral "mastication areas," differentneural mechanisms between mammalian taxa, neurophysiologic/morphologicinteractions, and biochemical factors within the total milieuof mammalian mastication are discussed.     

Double function of aptychi (Ammonoidea) as jaw elements and opercula

Lehmann, U. & Kulicki, C. 1990 10 15: Double function of aptychi (Ammonoidea) as jaw elements and opercula. Lethaia , Vol. 23, pp. 325–331. Oslo. ISSN 0024–1164.
Aptychi are calcitic coverings on the outer surface of organic ammonite lower jaws. They are similar in shape to that of the corresponding ammonite apertures. This observation and additional features of many aptychi are in harmony with their former interpretation as protective opercula. We suggest that they served as opercula in addition to functioning as jaws. The primary function of the lower jaws was thus secondarily extended to that of protective shields when they acquired their calcitic covering, while as lower jaws their importance dwindled to that of a more passive abutment. Phylogenetically, this seems to have started slowly in some anaptychi and became obvious with the first aptychi. ▭ Ammonites, aptychus, operculum, jaw apparatus, evolution, function .     

A new transitional sauropodomorph dinosaur from the Early Jurassic of South Africa and the evolution of sauropod feeding and quadrupedalism

Aardonyx celestae gen. et sp. nov. is described from the upper Elliot Formation (Early Jurassic) of South Africa. It can be diagnosed by autapomorphies of the skull, particularly the jaws, cervical column, forearm and pes. It is found to be the sister group of a clade of obligatory quadrupedal sauropodomorphs (Melanorosaurus + Sauropoda) and thus lies at the heart of the basal sauropodomorph–sauropod transition. The narrow jaws of A. celestae retain a pointed symphysis but appear to have lacked fleshy cheeks. Broad, U-shaped jaws were previously thought to have evolved prior to the loss of gape-restricting cheeks. However, the narrow jaws of A. celestae retain a pointed symphysis but appear to have lacked fleshy cheeks, demonstrating unappreciated homoplasy in the evolution of the sauropod bulk-browsing apparatus. The limbs of A. celestae indicate that it retained a habitual bipedal gait although incipient characters associated with the pronation of the manus and the adoption of a quadrupedal gait are evident through geometric morphometric analysis (using thin-plate splines) of the ulna and femur. Cursorial ability appears to have been reduced and the weight bearing axis of the pes shifted to a medial, entaxonic position, falsifying the hypothesis that entaxony evolved in sauropods only after an obligate quadrupedal gait had been adopted.     

Ontogeny of the jaw apparatus and suspensorium of the Tetraodontiformes

Konstantinidis, P. and Johnson, G. David 2012. Ontogeny of the jaw apparatus and suspensorium of the Tetraodontiformes. —Acta Zoologica (Stockholm) 93 : 351–366. The jaw apparatus and suspensorium of adult Tetraodontiformes are well adapted to a durophagous feeding habit. Anatomical indicators are the short, stout jaws and a suspensorium in which the quadrate lies in the same vertical plane as the autopalatine. In contrast, the palatoquadrate of larval Tetraodontiformes generally resembles that of larval percomorphs – a more posteriorly positioned quadrate and a slender and long Meckelian cartilage. Among Tetraodontiformes, the Triacanthodidae retain a protrusible upper jaw and a versatile suspensorium. The jaws of the Balistoidei have greater mobility achieved by a reduced autopalatine that has lost its bony contact with the suspensorium. In contrast to the Balistoidei, the beak‐like jaws of the Tetraodontoidei lack individual teeth in the biting part of the jaws. The autopalatine is enlarged, which results in immobilization of the ethmopalatine articulation. The Ostraciidae are exceptional in having the distal part of the autopalatine reduced, while the proximal part remains attached to the suspensorium.     

Functional morphology of the pharyngeal jaw apparatus in moray eels

Moray eels (Muraenidae) are a relatively large group of anguilliform fishes that are notable for their crevice-dwelling lifestyle and renowned for their ability to consume large prey. Morays apprehend their prey by biting and then transport prey by extreme protraction and retraction of their pharyngeal jaw apparatus. Here, we present a detailed interpretation of the mechanisms of pharyngeal jaw transport based on work with Muraena retifera. We also review what is known of the moray pharyngeal jaw apparatus from the literature and provide comparative data on the pharyngeal jaw elements and kinematics for other moray species to determine whether interspecific differences in morphology and behavior are present. Rather than comprising broad upper and lower processing tooth plates, the pharyngeal jaws of muraenine and uropterygiine morays, are long and thin and possess large, recurved teeth. Compared with the muraenines, the pharyngobranchials of the uropterygiines do not possess a horn-shaped process and their connection to the fourth epibranchial is dorsal rather than medial. In addition, the lower tooth plates do not exhibit a lateral groove that serves as a site of muscle attachment for the pharyngocleitheralis and the ventral rather than the lateral side of the lower tooth plate attaches to the fourth ceratobranchial. In all morays, the muscles positioned for protraction and retraction of the pharyngeal apparatus have undergone elongation, while maintaining the generalized attachment sites on the bones of the skull and axial skeleton. Uropterygiines lack a dorsal retractor muscle and we presume that retraction of the pharyngeal jaws is achieved by the pharyngocleitheralis and the esophagus. The fifth branchial adductor is greatly hypertrophied in all species examined, suggesting that morays can strongly adduct the pharyngeal jaws during prey transport. The kinematics of biting behavior during prey capture and transport resulted in similar magnitudes of cranial movements although the timing of kinematic events was significantly different and the duration of transport was twice as long as prey capture. We speculate that morays have evolved this alternative prey transport strategy as a means of overcoming gape constraints, while hunting in the confines of coral reefs.     

Glass-Breaking Pliers for the Preparation of Glass Knives Used in Ultramicrotomy

Pliers used for handling plate glass customarily have flat jaws, but a modification in design of the jaws—one convex and the other concave—facilitates breaking small pieces of glass along a score mark. An index mark on the concave jaw is aligned with the score, and closure of the jaws limited to a proper width by an adjusting screw in the handle.     

Ventilation and the origin of jawed vertebrates: a new mouth

This study investigates the origin of jaws by re-assessing homologies between the oropharyngeal regions of Agnatha and Chondrichthyes. In accordance with classical theory, jaws are interpreted as the most anterior arches of the ventilatory branchial basket. It is proposed that jaws first enlarged for a ventilatory function, i.e. closing the jaws prevented reflux of water through the mouth during forceful expiration. Next, they enlarged further to grasp prey in feeding. As they enlarged, the jaws tilted forward, squeezing the ancestral oral cavity in front of them ('old mouth') into a slit between the jaws and lips. Simultaneously, the anterior part of the pharynx behind the jaws was pulled forward and became a 'new mouth' (the buccal part of the buccopharyngeal cavity of gnathostomes). During the transition to gnamostomes, the premandibular cheeks and lips of the old mouth remained in place, and are represented in ammocoete lampreys, chimaeroids, and sharks. The stages in the evolution of gnathostomes, driven by selection for increasing activity, are modelled as: ancestral vertebrate (with unjointed branchial arches) to early pre-gnathostome (jointed internal arches and stronger ventilation) to late pre-gnadiostome (with mouth-closing, ventilatory 'jaws') to early gnathostome (feeding jaws).     

Eating without hands or tongue: specialization, elaboration and the evolution of prey processing mechanisms in cartilaginous fishes

The ability to separate edible from inedible portions of prey is integral to feeding. However, this is typically overlooked in favour of prey capture as a driving force in the evolution of vertebrate feeding mechanisms. In processing prey, cartilaginous fishes appear handicapped because they lack the pharyngeal jaws of most bony fishes and the muscular tongue and forelimbs of most tetrapods. We argue that the elaborate cranial muscles of some cartilaginous fishes allow complex prey processing in addition to their usual roles in prey capture. The ability to manipulate prey has evolved twice along different mechanical pathways. Batoid chondrichthyans (rays and relatives) use elaborate lower jaw muscles to process armored benthic prey, separating out energetically useless material. In contrast, megacarnivorous carcharhiniform and lamniform sharks use a diversity of upper jaw muscles to control the jaws while gouging, allowing for reduction of prey much larger than the gape. We suggest experimental methods to test these hypotheses empirically.