Tooth reorientation affects tooth function during prey processing and tooth ontogeny in the lesser electric ray, Narcine brasiliensis

The dental anatomy of elasmobranch fishes (sharks, rays and relatives) creates a functional system that is more dynamic than that of mammalian dentition. Continuous dental replacement (where new teeth are moved rostrally to replace older ones) and indirect fibrous attachment of the dentition to the jaw allow teeth to reorient relative to the jaw over both long- and short-term scales, respectively. In this study, we examine the processing behavior and dental anatomy of the lesser electric ray Narcine brasiliensis (Olfers, 1831) to illustrate that the freedom of movement of elasmobranch dentition allows a functional flexibility that can be important for complex prey processing behaviors. From static manipulations of dissected jaws and observations of feeding events in live animals, we show that the teeth rotate during jaw protrusion, resulting in a secondary grasping mechanism that likely serves to hold prey while the buccal cavity is flushed free of sediment. The function of teeth is not always readily apparent from morphology; in addition to short-term reorientation, the long-term dental reorientation during replacement allows a given tooth to serve multiple functions during tooth ontogeny. Unlike teeth inside the mouth, the cusps of external teeth (on the portion of the tooth pad that extends past the occlusal plane) lay flat, such that the labial faces act as a functional battering surface, protecting the jaws during prey excavation.     

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.     

Tooth replacement pattern of Coloborhynchus robustus (Pterosauria) from the Lower Cretaceous of Brazil

The well preserved anterior upper and lower jaw fragment of an adult specimen of Coloborhynchus robustus (Pterosauria: Ornithocheiridae), SMNK 2302 PAL, allowed investigations of the replacement pattern of the dentition macroscopically and by using CT scans. The quantification of the dentition by Zahnreihen, Z-Spacing, and replacement waves indicates a complex pattern of different replacement stages in which large gaps within the dentition were avoided. The specialized prey-catching apparatus of Coloborhynchus thus could retain its function even following tooth replacement. The replacement process in the specimen took about 2/3 of the total life-time of a tooth, and damaged teeth in the anterior jaw region may have been replaced more rapidly than posterior teeth. The distolingual replacement of the functional teeth delayed the time of their shedding in comparison with the circular resorption present in crocodiles. In contrast to these, the distolingual position of the replacement tooth did not decrease the biomechanical stability of the functional tooth, which can also be observed as a convergence in other thecodont dentitions, e.g., recent carnivore mammals. Teeth were shed when their replacement had reached about 60% of the full-grown height. A comparison of the observed pattern is constricted by the preservation and preparation of other specimens. Unfortunately, no known specimen in public collections reaches the quality of Coloborhynchus robustus, SMNK 2302 PAL, so that comparable patterns in other specimens are not likely to be detected.     

Dentition patterns among Pacific and Western Atlantic butterflyfishes (Perciformes,Chaetodontidae): relationship to feeding ecology and evolutionary history

Synopsis The jaw dentition of fifteen species of Pacific and Western Atlantic chaetodontid butterflyfishes was examined in light of their feeding habits and phylogenetic relationships. The ancestral tooth pattern is typical of many of the butterflyfishes, and variations on this basic pattern involve changes in the arrangement, length and number of teeth, and tooth shape to a lesser extent. Many of the more derived conditions can be explained by simple changes in relative jaw shape and size. Despite what appears to be adequate time for evolutionary changes to occur between the Pacific and Western Atlantic faunas, many species retain the generalized tooth arrangement permitting efficient exploitation in a very generalized manner. However, Pacific species as a whole show more specialized morphologies for hard coral feeding than do Western Atlantic species. Cases of parallel and divergent evolution are identified between and among the two faunas. Most morphological change associated with feeding in butterflyfishes is confined to the anterior region of the head, and particularly a few key elements. Suggestions for future morphological studies on the chaetodontids are outlined.     

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.     

Teeth of Embryos in Lamniform Sharks (Chondrichthyes: Elasmobranchii)

The dentitions of lamniform sharks possess a unique heterodonty, the lamnoid tooth pattern. However, in embryos, there are 'embryonic' and 'adult' dentitions. The teeth in the embryonic dentition are peg-like and appear to be attached to the jaw in an acrodont fashion. The adult dentition is characterized by the presence of replacement tooth series with the lamnoid tooth pattern. The embryonic–adult transition in dentitions appears at around 30–60cm TL. Tooth replacement generally begins before birth in embryos with adult dentitions. The adult dentition becomes functional just before or after parturition. An embryo of one species (Lamna nasus) shows a tooth directly on the symphysis of the upper jaws, marking the first record of a medial tooth for the order Lamniformes.     

On the geometry and mechanics of tooth position in the white shark,Carcharodon carcharias

The teeth of captured specimens, of prepared museum specimens, and of high-speed videotape images of the white shark, Carcharodon carcharias, were compared with respect to (1) deviation of each tooth from the animal's midline and (2) the crown angle of the functional teeth along the jaw margin. Tooth position was measured either directly using a meter stick apparatus or derived from tracings of the video footage. Tooth positions were not statistically unique in any region of the upper or lower jaw but demonstrated less variability in crown angle within 30° of the midline (71.48° ± 10°). Videotape analysis of feeding sharks indicated an 8.7° increase in crown angle of the centermost teeth during bites where the jaws were closed through an angle of 20–35° and a 15.7° reduction in this same parameter during jaw adduction through 35° or more. Such changes in tooth orientation (relative to the rear of the buccal cavity) are ascribed to flexure of the cartilaginous jaws and cranium by the cranial musculature and possibly also to sliding of the tooth bed over the jaw. Outward rotation of the teeth and jaw rami describes a plucking action during feeding or prey sampling, while larger bites rotate the frontmost teeth inward towards the gullet. Functionally, this may make the teeth more effective at grasping small prey items or gouging chunks from larger prey. However, testing of the load required to remove teeth showed no significant increase in tensile resistance with reduced crown angle. © 1995 Wiley-Liss, Inc.     

Plate-like permanent dental laminae of upper jaw dentition in adult gobiid fish, Sicyopterus japonicus

Sicyopterus japonicus (Teleostei, Gobiidae) possesses a unique upper jaw dentition different from that known for any other teleosts. In the adults, many (up to 30) replacement teeth, from initiation to attachment, are arranged orderly in a semicircular-like strand within a capsule of connective tissue on the labial side of each premaxillary bone. We have applied histological, ultrastructural, and three-dimensional imaging from serial sections to obtain insights into the distribution and morphological features of the dental lamina in the upper jaw dentition of adult S. japonicus. The adult fish has numerous permanent dental laminae, each of which is an infolding of the oral epithelium at the labial side of the functional tooth and forms a thin plate-like structure with a wavy contour. All replacement teeth of a semicircular-like strand are connected to the plate-like dental lamina by the outer dental epithelium and form a tooth family; neighboring tooth families are completely separated from each other. The new tooth germ directly buds off from the ventro-labial margin of the dental lamina, whereas no distinct free end of the dental lamina is present, even adjacent to this region. Cell proliferation concentrated at the ventro-labial margin of the dental lamina suggests that this region is the site for repeated tooth initiation. During tooth development, the replacement tooth migrates along a semicircular-like strand and eventually erupts through the dental lamina into the oral epithelium at the labial side of the functional tooth. This unique thin plate-like permanent dental lamina and the semicircular-like strand of replacement teeth in the upper jaw dentition of adult S. japonicus probably evolved as a dental adaptation related to the rapid replacement of teeth dictated by the specialized feeding habit of this algae-scraping fish.     

The mechanics of cutting and the form of shark teeth (Chondrichthyes,Elasmobranchii)

Summary A rich engineering literature exists that is applicable to many aspects of vertebrate jaw mechanics and has been referred to in many studies in this sector. But mechanical engineering technology has provided few theoretical bases that are directly helpful in the study of predator teeth. Hence, analyses of puncturing and slicing functions of these teeth have lacked a firm physical technology as a background. Predator teeth have evolved to pierce and cut animal tissues that are usually compliant in that they readily undergo relatively large deformations under applied stress before they actually yield. The bulk of engineering theory is directed toward such noncompliant materials as wood and metal, the design of tools that cut them, and the mechanics involved in this. The purpose of the present paper is to scan the mechanical implications of different tooth designs, pose hypotheses that relate to primary considerations of the physics of cutting compliant substrates, and offer a preliminary approach that is intended as a useful guide to further studies on sharks and on other vertebrate groups. Thus, in this paper I have attempted to formulate some tentative and preliminary generalizations concerning the mechanics of cutting compliant materials. Then comes a survey of the teeth of a particular group of predators, three families of sharks, in terms of these preliminary formulations. The approach views the shark teeth in isolation from the complex cranial mechanism (presently under study) that functionally integrates with the teeth. Therefore, adaptive conclusions are minimal, because the evolutionary significance of tooth form cannot properly be assessed outside of an integrated study. However, certain correlations do exist between structural tooth characteristics and mechanics. Slender, smooth-edged (or nearly so) teeth can readily pierce prey, but are of less use in slicing it. Such teeth are typical of the lower jaw dentition in many sharks and, in a few species, they are present in both upper and lower jaws. Usually these slender teeth display a reversed curvature at their tips, so that although most of the tooth's crown is curved inward toward the mouth cavity, the tip is turned outward. This outward turning of the tip can enhance the probability of initial prey penetration, without much compromising the prey-retaining properties of the inward curvature of the greater, more proximal portion of the tooth. Many sharks possess upper teeth with serrations along the edges. The serrations vary from one species to another in coarseness and in distribution along tooth edges. Serrated teeth can make greater use of the available biting forces, and they have a greater cutting effect than do smooth-edged teeth. These latter depend upon friction which, because the coefficient friction is always less than 1.0 (often very much less), can make use of only a fraction of the total bite force. However, smooth tooth blades can pierce prey with less resistance and are less prone to binding (becoming immobilized) in the prey tissue. In many shark species serrations are concentrated along the proximal portions of the tooth crown, where the bases of adjacent teeth are in near contact along the jaw margin. In these regions food can be pressed during feeding, resulting in a binding of the teeth in the prey. Release of the binding must be accomplished by cutting the jammed food, to permit clearance of the prey material so it can slip past the tooth rows. The more prominent serrations in such regions may act to puncture and slice the jammed tissue. It is noted that commercial saws are typically designed in various ways to promote clearance between adjacent saw teeth. The pitch or rake of the teeth of sharks is discussed, as is the overall form of the tooth rows along the jaw margins. The relationship between the distribution of teeth along the jaw margins and surface irregularities of the prey surfaces is also considered.     

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.     

The jaw lever system in ungulates: a new model

In ungulates the distance from the jaw joint to the last molar is approximately the same as that of the grinding tooth row length. An hypothesis is presented that attempts to explain why ungulate grinding teeth are positioned where they are along the jaw. If the jaw joint on the balancing side serves as the fulcrum in anisognathus animals, a region along the jaw is defined, corresponding to where teeth are actually found, where rather simple muscle action can apply equal forces at any point. The ability to produce the same force at any point in this region, as such, may not be the critical feature since anterior or posterior to this region, tooth placement produces either a relatively inefficient or an unstable condition.     

Jaw mechanism and dental function in the late cretaceous basal eusuchian Iharkutosuchus

Iharkutosuchus makadii is a basal eusuchian crocodylian with multicusped teeth discovered from the Upper Cretaceous of Hungary. Skull and dentition morphology indicates an active food processing for this crocodylian. First among crocodylians, a combination of different analyses, including cranial adductor muscle reconstruction, tooth wear pattern, and enamel microstructure studies, is applied here to support this hypothesis. Data provide unambiguous evidence for significant dental occlusion that was a result of a unique, transverse mandibular movement. Reconstruction of the jaw adductors demonstrates strong muscles responsible for slow but active jaw closure as the motor of transverse jaw movement; nevertheless muscles producing rapid jaw closure were reduced. Macrowear orientations show a dominantly transverse movement of the mandibles completed by a slight anteroposterior component. Along with quadrate morphology, macrowear further indicates that this motion was accomplished by alternate rotation of the mandibles about the quadrate condyles. Dental morphology and wear patterns suggest two types of power stroke: a slicing–crushing stroke associated dominantly with anterior tooth–food–tooth contact (with a low degree of transverse mandibular movement) during in the early stage of mastication, and a grinding stroke with significant posterior tooth–tooth contact and a dynamic transverse movement occurring later. The patterns of microwear show a diverse diet for Iharkutosuchus including both soft and hard items. This is also supported by the microstructure of the thick, wrinkled enamel built up mostly by poorly developed columnar units. Based on wear patterns, ontogenetic variation in feeding habits of Iharkutosuchus is also recognized. J. Morphol., 2009. © 2009 Wiley‐Liss, Inc.     

Marginal tooth-bearing bones in the lower jaw of the recent australian lungfish,Neoceratodus forsteri (Osteichthyes,Dipnoi)

Developmental studies of the Recent Australian lungfish, Neoceratodus forsteri, show that this species has two sets of functional tooth-bearing bones in the lower jaw of young hatchlings. These coincide with an early stage in the life history when the fish is strictly carnivorous. In N. forsteri, a paired tooth-bearing dentary and an unpaired symphyseal bone and tooth develop slightly later than the permanent vomerine, prearticular, and pterygopalatine tooth plates, which appear at stage 44 of development, and erupt with the permanent dentition between stages 46 and 48, when the hatchling first starts to feed on small aquatic invertebrates. At these stages of development, all of the teeth are long, sharp, and conical and help to retain prey items in the mouth. Disappearance of the transient dentition coincides with complete eruption of the permanent tooth plates and precedes the change to an omnivorous diet. Existence of a transient marginal dentition in this species of lungfish suggests that the presence of an apparently similar marginal dentition in adults of many species of Palaeozoic dipnoans should be considered in phylogenetic analyses of genera within the group, and when analysing the relationships of dipnoans with other primitive animals. © 1995 Wiley-Liss, Inc.     

Tooth replacement and growth in the young green iguana,Iguana iguana

A study using eight rapidly growing young green iguanas (Iguana iguana; initial mean weight 68.0 ± 3.8 gm) examined the changes in the wave replacement of teeth, the increased size of the teeth, and the posterior migration of tooth positions over a period of 16 weeks. The teeth increase in width as the lizards grow. The tooth positions shifted posteriorly, providing adequate space for the larger replacement teeth. These observations suggest that the wave replacement of teeth allows for growth of the dentition in length and height adequate to maintain tooth size in proportion to the overall size of the individual.     

The functional significance of morphological variation of the human mandible and masticatory muscles

A review is given of what is known about the functional significance of variation of the morphology of the human mandible and jaw muscles. First, the mandible is a lever transferring muscular forces to the teeth. The angle between corpus and ramus and the width of the ramus are particularly relevant in this respect as they determine the mechanical advantage of the lever system and the capacity for sagittal (open-close) movement. The stability of the mandible in asymmetric bites is especially affected by the ratio between the intermolar and intercondylar distances. The repertoire of bite forces that can be generated at any tooth and the loading pattern of the temporomandibular joint are strongly dependent on the relative size of the masseter, temporalis and medial pterygoid muscles. Second, executing its function as a lever, the mandible is subjected to shearing, bending and torsional forces. The bony parts harbouring the teeth, joints and muscle attachments serve to counter these forces; additional strength is needed in three areas i.e. in the symphysis, the condylar neck and in the transition area between corpus and ramus. In human populations there are clear-cut patterns of correlation between some facial skeletal traits, jaw joint morphology and strength and line of action of the jaw muscles. As a result, facial morphologies can be distinguished with marked differences in mechanical performance of their masticatory apparatus. It is suggested that they emerge as a result of diverging environmental influences during postnatal growth.     

The eruption times of permanent teeth in boys and girls in the Stormarn District, Schleswig-Holstein (Germany)

In a longitudinal study in two small towns in southern Schleswig-Holstein (Ammersbek and Ahrensburg, District Stormarn; 9155 inhabitants) we investigated 2832 oral findings of 1396 patients (711 males, 685 females). The minimum age was 1.51 years, and the maximum age was 25.50 years. The dental findings were collected over a period of about 20 years (1982-2002). The oral findings per child were assessed between one and eight times. The eruption times of teeth in females are earlier than those for the same teeth in males. Further, the permanent dentition in females is completed earlier than in males. In both sexes the tooth eruption occurs symmetrically in both jaws. The comparison of both jaws revealed a slightly advanced eruption of the lower jaw teeth in both sexes. There is a noteworthy change in the eruption sequence of the teeth. In contrast to other reports we observed that the eruption of the canine proceeds the eruption of the second molar. We found no acceleration of the dentition when compared with other reports and could confirm the rules of tooth eruption in man. Conclusion: Oral examination of teeth is a simple tool to calculate tooth eruption intervals. This first investigation on a population of Schleswig-Holstein revealed a change in the eruption sequence of permanent teeth. These findings are relevant for dental treatment planning and should be reconfirmed at certain intervals.