Form and function of the feeding apparatus of Alligator mississippiensis

The architecture of the jaw muscles and their tendons of Alligator mississippiensis is described and their function examined by electromyography. Alligator grabs its prey with forward lunges or rapid lateral movements of the head. It does not engage in regular masticatory cycles. Prey is manipulated by inertial movements and the tongue does not appear to play any role in transport. The Mm. adductor mandibulae externus, adductor mandibulae posterior, and pterygoideus activate bilaterally and simultaneously during rapid closing or crushing. The M. pterygoideus does not act during prey holding whereas the Mm. adductor mandibulae externus, adductor mandibulae posterior continue to be active. The Mm. depressor mandibulae and intramandibularis are variably active during both jaw opening and closing.     

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.     

Feeding in Atractaspis (Serpentes: Atractaspididae): a study in conflicting functional constraints

African fossorial colubroid snakes of the genus Atractaspis have relatively long fangs on short maxillae, a gap separating the pterygoid and palatine bones, a toothless pterygoid, and a snout tightly attached to the rest of the skull. They envenomate prey with a unilateral backward stab of one fang projected from a closed mouth. We combined structural reanalysis of the feeding apparatus, video records of prey envenomation and transport, and manipulations of live and dead Atractaspis to determine how structure relates to function in this unusual genus of snakes. Unilateral fang use in Atractaspis is similar to unilateral slashing envenomation by some rear-fanged snakes, but Atractaspis show no maxillary movement during prey transport. Loss of pterygoid teeth and maxillary movement during transport resulted in the inability to perform. 'pterygoid walk' prey transport. Atractaspis transport prey through the oral cavity using movement cycles in which mandibular adduction, anterior trunk compression, and ventral flexion of the head alternate with mandibular abduction and extension of head and anterior trunk over the prey. Inefficiencies in manipulation and early transport of prey are offset by adaptability of the envenomating system to various prey types in both enclosed and open spaces and by selection of prey that occupy burrows or tunnels in soil. Atractaspis appears to represent the evolutionary endpoint of a functional conflict between envenomation and transport in which a rear-fanged envenomating system has been optimized at the expense of most, if not all, palatomaxillary transport function.     

Mosasaurus beaugei Arambourg, 1952 (Squamata, Mosasauridae) from the Late Cretaceous phosphates of Morocco

Mosasaurus beaugei Arambourg, 1952 was based on isolated teeth from the Maastrichtian phosphatic deposits of Morocco. The recent discovery of new material, including skull and mandibular remains, improves our knowledge of this species. M. beaugei shares the following synapomorphies with the genus Mosasaurus: large teeth bearing two prominent carinae and with asymmetrical labial and lingual surfaces, the labial one being flattened and strongly facetted and the lingual one being convex; premaxillae with a small pointed rostrum and dentary without rostrum; palatal elements closely united; coronoid with very large ventromedial process overlying the prearticular. M. beaugei is characterised by the following autapomorphies: 12-13 maxillary teeth; marginal teeth bearing 3-5 prisms on the labial surface and 8-9 on the lingual one; palatine with posterior border concave and perpendicular to the long axis of the skull; splenial visible laterally on half of the dentary ventral surface; coronoid with anterior wing well developed and bearing two notches. M. beaugei is only known to date in the Maastrichtian phosphates of Morocco.     

Dentition and diet in snakes: adaptations to oophagy in the Australian elapid genus Simoselaps

Most small fossorial proteroglyphous Australian snakes of the genus Simoselaps feed on adult lizards, but the species of one lineage (the semifasciatus group) feed exclusively on the eggs of squamate reptiles. Examination of cleared, alizarin preparations showed that dentition of the saurophagous species is similar to that of other elapids, but dentition of the oophagous taxa is highly modified. The anterior (palatine and maxillary) teeth other than the fangs are reduced in size and number whereas those of the pterygoid (and in S. 'ropert ', the dentary) are enlarged posteriorly, becoming compressed along a longitudinal plane and angled medially. The shape of the pterygoid and quadrate is also modified.
Two Simoselaps species with broader diets (eating both adult lizards and their eggs) show typical 'saurophagous' dentition in one case, 'oophagous' dentition in the other, showing that either type of dentition can be used to capture and ingest either type of prey. We suggest functional explanations for the dentitional modifications in the egg-eating snakes, primarily in terms of the advantages of applying considerable force to the eggshell. Oophagous modifications within Simoselaps are convergent with those seen in several independently-derived lineages of oophagous colubrid snakes, but (perhaps because of the presence of the fang) differ in having the enlarged blade-like teeth on the pterygoid or dentary rather than the maxilla.     

Functional morphology of the palato‐maxillary apparatus in “Palatine dragging” snakes (Serpentes: Elapidae: Acanthophis,Oxyuranus)

Elapid snakes have previously been divided into two groups (palatine erectors and palatine draggers) based on the morphology and inferred movements of their palatine bone during prey transport (swallowing). We investigated the morphology and the functioning of the feeding apparatus of several palatine draggers (Acanthophis antarcticus, Oxyuranus scutellatus, Pseudechis australis) and compared them to published records of palatine erectors. We found that the palatine in draggers does not move as a straight extension of the pterygoid as originally proposed. The dragger palato‐pterygoid joint flexes laterally with maxillary rotation when the mouth opens and the jaw apparatus is protracted and slightly ventrally during mouth closing. In contrast, in palatine erectors, the palato‐pterygoid joint flexes ventrally during upper jaw protraction. In draggers, the anterior end of the palatine also projects rostrally during protraction, unlike the stability of the anterior end seen in erectors. Palatine draggers differ from palatine erectors in four structural features of the palatine and its relationships to surrounding elements. The function of the palato‐pterygoid bar in both draggers and erectors can be explained by a typical colubroid muscle contraction pattern, which acts on a set of core characters shared among all derived snakes. Although palatine dragging elapids share a fundamental design of the palato‐maxillary apparatus with all higher snakes, they provide yet another demonstration of minor structural modifications producing functional variants. J. Morphol. 2010. © 2009 Wiley‐Liss, Inc.     

Functional morphology of bite mechanics in the great barracuda (Sphyraena barracuda)

The great barracuda, Sphyraena barracuda, is a voracious marine predator that captures fish with a swift ram feeding strike. While aspects of its ram feeding kinematics have been examined, an unexamined aspect of their feeding strategy is the bite mechanism used to process prey. Barracuda can attack fish larger than the gape of their jaws, and in order to swallow large prey, can sever their prey into pieces with powerful jaws replete with sharp cutting teeth. Our study examines the functional morphology and biomechanics of 'ram-biting' behavior in great barracuda where the posterior portions of the oral jaws are used to slice through prey. Using fresh fish and preserved museum specimens, we examined the jaw mechanism of an ontogenetic series of barracuda ranging from 20 g to 8.2 kg. Jaw functional morphology was described from dissections of fresh specimens and bite mechanics were determined from jaw morphometrics using the software MandibLever (v3.2). High-speed video of barracuda biting (1500 framess(-1)) revealed that prey are impacted at the corner of the mouth during capture in an orthogonal position where rapid repeated bites and short lateral headshakes result in cutting the prey in two. Predicted dynamic force output of the lower jaw nearly doubles from the tip to the corner of the mouth reaching as high as 58 N in large individuals. A robust palatine bone embedded with large dagger-like teeth opposes the mandible at the rear of the jaws providing for a scissor-like bite capable of shearing through the flesh and bone of its prey.     

Tooth implantation and replacement in Sauropterygia

Tooth replacement and implantation of Sauropterygia is described with special reference to the generaPlacodus andNothosaurus. Tooth replacement is horizontal, with the exception of the enlarged crushing tooth plates on the maxilla, palatine, and dentary ofPlacodus (placodonts), which are replaced vertically. Tooth implantation is thecodont, with variable ankylosis of the base of the root. Sauropterygia is unique compared to other reptiles in that replacement teeth are “alveolarized.” The alveolarization of replacement teeth adds to the evidence supporting of a monophyletic Sauropterygia (Placodontia plus Eosauropterygia).      

Eating with a saw for a jaw: Functional morphology of the jaws and tooth‐whorl in Helicoprion davisii

The recent reexamination of a tooth‐whorl fossil of Helicoprion containing intact jaws shows that the symphyseal tooth‐whorl occupies the entire length of Meckel's cartilage. Here, we use the morphology of the jaws and tooth‐whorl to reconstruct the jaw musculature and develop a biomechanical model of the feeding mechanism in these early Permian predators. The jaw muscles may have generated large bite‐forces; however, the mechanics of the jaws and whorl suggest that Helicoprion was better equipped for feeding on soft‐bodied prey. Hard shelled prey would tend to slip anteriorly from the closing jaws due to the curvature of the tooth‐whorl, lack of cuspate teeth on the palatoquadrate (PQ), and resistance of the prey. When feeding on soft‐bodied prey, deformation of the prey traps prey tissue between the two halves of the PQ and the whorl. The curvature of the tooth‐whorl and position of the exposed teeth relative to the jaw joint results in multiple tooth functions from anterior to posterior tooth that aid in feeding on soft‐bodied prey. Posterior teeth cut and push prey deeper into the oral cavity, while middle teeth pierce and cut, and anterior teeth hook and drag more of the prey into the mouth. Furthermore, the anterior‐posterior edges of the teeth facilitate prey cutting with jaw closure and jaw depression. The paths traveled by each tooth during jaw depression are reminiscent of curved pathways used with slashing weaponry such as swords and knifes. Thus, the jaws and tooth‐whorl may have formed a multifunctional tool for capturing, processing, and transporting prey by cyclic opening and closing of the lower jaw in a sawing fashion. J. Morphol. 276:47–64, 2015. © 2014 Wiley Periodicals, Inc.     

Morphogenesis in hatchery-reared larvae of the black rockfish,Sebastes schlegeli,and its relationship to the development of swimming and feeding functions

The developmental sequence of morphological characteristics related to swimming and feeding functions was investigated in hatchery-reared larvae and juveniles ofSebastes schlegeli, a viviparous scorpaenid. The fish were extruded at an early larval stage, when the mean body size was 6.23 mm TL. Fin-ray rudiments became visible at 9.0 mm TL in the dorsal and anal fins, at 8.0 mm TL in the pectoral and pelvic fins and 6.0 mm TL (size at extrusion) in the caudal fin. Completion of segmentation of soft rays in the dorsal and anal fins was attained by 14 mm TL and in all fins by 17 mm TL. Branching of soft rays in the respective fins started and was completed considerably later than the completion of segmentation, as well as ossification of the fin-supports. Morphological transformation from larva to juvenile was apparently completed by about 17 mm TL. Although the completion of basic juvenile structures was attained by transformation at that body size, succeeding morphological changes occurred between 17 mm and 32 mm TL. Newly-extruded larvae possessed one or two teeth on the lower pharyngeal and pharyngobranchials 3 and 4, but lacked premaxillary, dentary, palatine and prevomer teeth. The fish attained full development of gill rakers and gill teeth by 15 mm TL, the upper and lower pharyngeal teeth subsequently developing into a toothplate. Development of the premaxillary, dentary and palatine teeth was completed at about 30 mm TL, by which time loop formation of the digestive canal and the number of pyloric caeca had attained the adult condition. The developmental sequence of swimming and feeding functions during larval and early juvenile periods appeared to proceed from primitive functions to advanced or complex ones, from the ability to produce propulsive force to that of swimming with high maneuverability and from development of the irreducible minimum function of passing food into the stomach to the ability to actively capture prey via passive food acquisition with the gill rakers and gill teeth. The relationship of morphological development to the behavior and feeding activity of artificially-produced hatchlings is also discussed.     

Anatomical study of the skull of amphisbaenian Diplometopon zarudnyi (Squamata,Amphisbaenia)

This study investigates the amphisbaenian species skull which includes cranium, lower jaw and hyoid apparatus. The medial dorsal bones comprise the premaxilla, nasal, frontal and parietal. The premaxilla carries a large medial tooth and two lateral ones. The nasals are paired bones and separated by longitudinal suture. Bones of circumorbital series are frontal, orbitosphenoid and maxilla. The occipital ring consists of basioccipital, supraoccipital and exooccipital. Supraoccipital and basioccipital are single bones while the exo-occipitals are paired. The bones of the palate comprise premaxilla, maxilla, septomaxilla, palatine, pterygoid, ectopterygoid, basisphenoid, parasphenoid, orbitosphenoid and laterosphenoid. Prevomer and pterygoid teeth are absent. Palatine represent by two separate bones. The temporal bones are clearly visible. The lower jaw consists of the dentary, articular, coronoid, supra-angular, angular and splenial. The hyoid apparatus is represented by a Y-shaped structure. The mandible is long and is suspended from the braincase via relatively short quadrate. There is an extensive contact between the long angular and the large triangular coronoid. Thus inter-mandibular joint is bridged completely by the angular and consequently, the lower jaws are relatively rigid and kinetic. The maxillae are suspended from the braincase largely by ligaments and muscles rather than through bony articulation. In conclusion, the skull shape affects feeding strategy in Diplometopon zarudnyi. The prey is ingested and transported via a rapid maxillary raking mechanism.     

A functional analysis of food procurement in two surgeonfish species,Acanthurus nigrofuscus andCtenochaetus striatus (Acanthuridae)

Synopsis The mechanisms of food procurement in the surgeonfishesCtenochaetus striatus andAcanthurus nigrofuscus from the Great Barrier Reef were determined by functional analyses of the jaws and associated structural elements (based on myological and osteological examinations and X-ray photographs) and by video analyses of actions of the mouth and body during feeding.Acanthurus nigrofuscus has relatively robust jaw bones. The movement of the elements during mouth opening is limited with a mean maximum gape angle of 112.8°. Each bite is relatively fast and is characterized by a quick nip at algal filaments, usually followed by a sidewads flick of the head. The jaws bear several broad multidenticulate teeth. It appears that these teeth engage turf algal strands which are either sheared during mouth closure or torn off as the head flicks sideways. InC. striatus, the jaw bones are considerably lighter than those ofA. nigrofuscus. There is much greater movement of the elements during mouth opening, resulting in a mean maximum gape angle of 177.6°. Each bite is slower than inA. nigrofuscus and is characterized by a wide gape as the mouth is applied to the substratum followed by a quick, upward flick of the lower jaw, with no sideways flick of the head. The jaws bear numerous elongate flexible teeth, with expanded incurved denticulate tips; those on the dentary often possessing a pointed blade-like process. It appears that these teeth brush particulate and epiphytic material from the surface of the turf algal strands and other substrata. These observations demonstrate howA. nigrofuscus andC. striatus are able to remove microalgae and detritus, respectively, from the same substratum. The results also demonstrate how relatively small differences in morphology can have a profound influence on the feeding abilities and trophic ecology of fishes.     

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

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

Revision of Habrosaurus Gilmore (Caudata; Sirenidae) and relationships among sirenid salamanders

The sirenid salamander Habrosaurus is revised and redescribed based on skull elements and vertebrae from the middle Campanian–middle Palaeocene of the North American Western Interior. Habrosaurus differs from the Cenozoic (Eocene–Recent) sirenids Siren and Pseudobranchus in a suite of cranial and vertebral plesiomorphies, one vertebral character of uncertain polarity and five apomorphies describing the structure of the dentary, atlas and tooth crowns. Two species are identified based on dental characters: the type species H. dilatus (late Maastrichtian–middle Palaeocene) has stout marginal and palatal teeth with bulbous crowns and prominent wear facets, whereas H. prodilatus sp. nov. (middle Campanian) has chisel-like marginal teeth (palatal teeth unknown) with weaker wear facets. Habrosaurus is argued to be the geologically oldest, undoubted sirenid and the sister-taxon of Siren  +  Pseudobranchus . Replacement of marginal teeth with a broad, horny beak in Siren and Pseudobranchus and the broad, bulbous marginal and palatal teeth in H. dilatus are proposed to be convergent strategies for achieving a crushing bite. The chisel-like teeth of H. prodilatus are interpreted as being transitional to the more specialized, crushing dentition of H. dilatus .     

Bone-Breaking Bite Force of Basilosaurus isis (Mammalia,Cetacea) from the Late Eocene of Egypt Estimated by Finite Element Analysis

Bite marks suggest that the late Eocence archaeocete whale Basilosaurus isis (Birket Qarun Formation, Egypt) fed upon juveniles of the contemporary basilosaurid Dorudon atrox. Finite element analysis (FEA) of a nearly complete adult cranium of B. isis enables estimates of its bite force and tests the animal’s capabilities for crushing bone. Two loadcases reflect different biting scenarios: 1) an intitial closing phase, with all adductors active and a full condylar reaction force; and 2) a shearing phase, with the posterior temporalis active and minimized condylar force. The latter is considered probable when the jaws were nearly closed because the preserved jaws do not articulate as the molariform teeth come into occulusion. Reaction forces with all muscles active indicate that B. isis maintained relatively greater bite force anteriorly than seen in large crocodilians, and exerted a maximum bite force of at least 16,400 N at its upper P³. Under the shearing scenario with minimized condylar forces, tooth reaction forces could exceed 20,000 N despite lower magnitudes of muscle force. These bite forces at the teeth are consistent with bone indentations on Dorudon crania, reatract-and-shear hypotheses of Basilosaurus bite function, and seizure of prey by anterior teeth as proposed for other archaeocetes. The whale’s bite forces match those estimated for pliosaurus when skull lengths are equalized, suggesting similar tradeoffs of bite function and hydrodynamics. Reaction forces in B. isis were lower than maxima estimated for large crocodylians and carnivorous dinosaurs. However, comparison of force estimates from FEA and regression data indicate that B. isis exerted the largest bite forces yet estimated for any mammal, and greater force than expected from its skull width. Cephalic feeding biomechanics of Basilosaurus isis are thus consistent with habitual predation.     

A possible relationship between aspects of dentition and feeding in the centrarchid and anabantoid fishes

Synopsis Certain components of dentition — teeth on the third basibranchial in the Centrarchidae and on the parasphenoid in the anabantoids (sensu lato) — are very rare elsewhere in higher teleostean fishes. Though these basibranchial and parasphenoid teeth in the two fish groups are on opposite sides of the oral cavity, it is hypothesized that they both developed as adaptations for gripping a particular category of food items, namely strong-clawed, hard-shelled, active animals that, once within the oral cavity, would try to crawl out again. A corollary to this hypothesis is that higher teleosts with extensive dentition in the central part of the oral cavity have a grasping jaw bite, which, unlike a piercing, shearing, or crushing jaw bite, does not necessarily kill the prey that is taken into the oral cavity.     

Morphological and functional bases of durophagy in the queen triggerfish,Balistes vetula (Pisces,tetraodontiformes)

Tetraodontiform fishes are characterized by jaws specialized for powerful biting and a diet dominated by hard-shelled prey. Strong biting by the oral jaws is an unusual feature among teleosts. We present a functional morphological analysis of the feeding mechanism of a representative tetraodontiform, Balistes vetula. As is typical for the order, long, sharp, strong teeth are mounted on the short, robust jaw bones of B. vetula. The neurocranium and suspensorium are enlarged and strengthened to serve as sites of attachment for the greatly hypertrophied adductor mandibulae muscles. Electromyographic recordings made from 11 cranial muscles during feeding revealed four distinct behaviors in the feeding repertoire of B. vetula. Suction is used effectively to capture soft prey and is associated with a motor pattern similar to that reported for many other teleosts. However, when feeding on hard prey, B. vetula directly bit the prey, exhibiting a motor pattern very different from that of suction feeding. During buccal manipulation, repeated cycles of jaw opening and closing (biting) were coupled with rapid movement of the prey in and out of the mouth. Muscle activity during buccal manipulation was similar to that seen during bite-captures. A blowing behavior was periodically employed during prey handling, as prey were forcefully “spit out” from the mouth, either to reposition them or to separate unwanted material from flesh. The motor pattern used during blowing was distinct from similar behaviors described for other fishes, indicating that this behaviors may be unique to tetraodontiforms. Thus B. vetula combines primitive behaviors and motor patterns (suction feeding and buccal manipulation) with specialized morphology (strong teeth, robust jaws, and hypertrophied adductor muscles) and a novel behavior (blowing) to exploit armored prey such as sea urchins molluscs, and crabs. © 1993 Wiley-Liss, Inc.     

Terrestrial feeding in the Mudskipper Periophthalmus (Pisces: Teleostei): A cineradiographic analysis

Mudskipping gobies (Periophthalminae) are among the most terrestrial of amphibious fishes. Specializations associated with terrestrial prey capture and deglutition have been studied in Periophthalmus koelreuteri by light and X-ray cinematography which permits direct visualization of pharyngeal jaw movement during deglutition. Anatomical specializations of the pharyngeal jaws are described and include depressible teeth, a large ventral process on ceratobranchial five, and muscular modifications.
Multiple terrestrial feedings occur by Periophthalmus without a return to the water, and cineradiography reveals that the buccal cavity is often filled with air during terrestrial excursions in contrast to some previous hypotheses. Transport of the prey into the oesophagus occurs primarily by anteroposterior movement of the upper pharyngeal jaw. The lower pharyngeal jaw plays a limited role in food transport and may serve primarily to hold and position prey. The bite between upper and lower pharyngeal jaws occurs between the anterior teeth, and both jaws are protracted together during raking of food into the oesophagus. Functional specializations correlated with terrestrial feeding include obligatory use of pharyngeal jaws for swallowing even small prey items and positioning of the prey in the pharynx by pharyngeal jaw and hyoid movements alone.
This analysis of terrestrial feeding allows hypotheses of design constraints imposed by the aquatic medium on fishes to be raised and tested.     

Diet and dentition in tropical ariid catfishes from Australia

Synopsis The diets of 13 species of ariid catfishes from the tropical waters of the Gulf of Carpentaria are described and compared. Fishes were collected from two estuaries and inshore and offshore marine areas. Up to 10 species have been recorded from a single estuary. Although all are carnivorous and consume a variety of prey, diet analyses and statistical ordination reveal three feeding guilds - piscivores, polychaete-eaters and molluscivores. The diets of most species are similar between sites. There are strong relationships between dietary guild and the size and arrangement of the palatine teeth. The piscivorous group of catfish (guild 1) have large mouths with relatively large multiple palatine tooth plates, either in a band or in a triangular pattern and armed with sharp recurved teeth. The primarily polychaete-feeding group (guild 2) have a variable mouth size but it is usually smaller than that of guild 1 fish; their palatine teeth plates are fewer and smaller, and they have small, sharp recurved teeth. Guild 3 eat mainly molluscs, and have a small mouth and large posteriorly situated palatine plates with globular, truncated teeth. Overlaps in diet between species are probably reduced by differential distribution patterns within estuaries and different habitat preferences. The mouth-width and tooth-plate arrangements of ariids in tropical Australia are suitable for dealing with broad classes of prey rather than specific items, conferring dietary flexibility. This probably optimizes the trade-off for most species between occupation of broad feeding niches and the ability to shift diet easily.     

Tooth wear and compensatory modification of the anterior dentoalveolar complex in humans

In populations living in environments where teeth wear severely, some compensatory modification of the dentoalveolar complex is thought to occur during life whereby functional occlusion is maintained as tooth substance is lost by wear. This study investigates one aspect of this modification process: Changes in the anterior dentoalveolar complex that are accompanied with wear were examined in a series of Japanese skeletal samples. In the prehistoric Japanese hunter-gatherer population heavy wear occurs over the entire dentition. The following changes were demonstrated to have occurred in the anterior segment of the dentition accompanied by wear on the anterior teeth: The anterior teeth tip lingually with wear up to a nearly upright position to fill in interproximal spaces that would have been generated by wear, and to maintain contact relations between adjacent teeth. At the same time, the anterior surface of the maxillary alveolar process also inclines lingually to a certain extent. The amount of lingual tipping is greater in the maxillary anterior teeth than in their mandibular antagonists. It is because of this discrepancy that, with age, the horizontal component of the overlap between maxillary and mandibular anterior teeth decreases, and their bite form changes from scissor bite to edge-to-edge bite. Lesser degrees of lingual tipping of the anterior teeth were also detected in the prehistoric agriculturists and historic Japanese populations. The variation in the degree of lingual tipping observed among the samples is explained by inter-population variation in severity and pattern of tooth wear. This and other evidence suggests that mechanisms that compensate for wear in the anterior dentition may be characteristic of all living human populations, independently of the degree of wear severity endured in their environments.