Biomechanics of cranial kinesis in birds: Testing linkage models in the white-throated sparrow (Zonotrichia albicollis)

Cranial kinesis in sparrows refers to the rotation of the upper jaw around its kinetic joint with the braincase. Avian jaw mechanics may involve the coupled motions of upper and lower jaws, in which the postorbital ligament transfers forces from the lower jaw, through the quadrate, pterygoid, and jugal bones, to the upper jaw. Alternatively, jaw motions may be uncoupled, with the upper jaw moving independently of the lower jaw. We tested hypotheses of cranial kinesis through the use of quantitative computer models. We present a biomechanical model of avian jaw kinetics that predicts the motions of the jaws under assumptions of both a coupled and an uncoupled mechanism. In addition, the model predicts jaw motions under conditions of force transfer by either the jugal or the pterygoid bones. Thus four alternative models may be tested using the proposed model (coupled jugal, coupled pterygoid, uncoupled jugal, uncoupled pterygoid). All models are based on the mechanics of four-bar linkages and lever systems and use morphometric data on cranial structure as the basis for predicting cranial movements. Predictions of cranial motions are tested by comparison to kinematics of white-throated sparrows (Zonotrichia albicollis) during singing. The predicted relations between jaw motions for the coupled model are significantly different from video observations. We conclude that the upper and lower jaws are not coupled in white-throated sparrows. The range of jaw motions during song is consistent with a model in which independent contractions of upper and lower jaw muscles control beak motion. © 1996 Wiley-Liss, Inc.     

The role of cranial kinesis in birds.

In birds, the ability to move the upper beak relative to the braincase has been the subject of many functional morphological investigations, but in many instances the adaptive significance of cranial kinesis remains unclear. Alternatively, cranial kinesis may be considered a consequence of the general design of the skull, rather than an adaptive trait as such. The present study reviews some results related to the mechanism and functional significance of cranial kinesis in birds. Quantitative three-dimensional X-ray has shown that in skulls morphologically as divers as paleognaths and neognaths the mechanism for elevation of the upper beak is very similar. One of the mechanisms proposed for avian jaw movement is a mechanical coupling of the upper and the lower jaw movement by the postorbital ligament. Such a mechanical coupling would necessitate upper beak elevation. However, independent control of upper and lower jaw has been shown to occur during beak movements in birds. Moreover, kinematic modeling and force measurements suggests that the maximum extensibility of collagen, in combination with the short distance of the insertion of the postorbital ligament to the quadrato-mandibular articulation do not constitute a block to lower jaw depression. The lower jaw ligaments serve to limit the maximal extension of the mandibula. It is suggested here that cranial kinesis in avian feeding may have evolved as a consequence of an increase in eye size. This increase in size led to a reduction of bony bars in the lateral aspect of the skull enabling the transfer of quadrate movement to the upper jaw. The selective forces favoring the development of a kinetic upper beak in birds may be subtle and act in different ecological contexts. Simultaneous movement of the upper and lower jaw not only increases the velocity of beak movements, but with elevated upper beak also less force is required to open the lower jaw. However, the penalty of increased mobility of elements in a lightweight skull and a large eye is potential instability of skull elements during biting, smaller bite forces and limitations on joint reaction forces. Such a lightly built, kinetic skull may have evolved in animals that feed on small plant material or insects. This type of food does not require the resistance of large external forces on the jaws as in carnivores eating large prey.     

Kinematics of the pharyngeal jaws during feeding in Oreochromis niloticus (Pisces,Perciformes)

Cichlids possess a complex pharyngeal jaw apparatus, the osteological components of which are two upper pharyngeal jaws, articulating with the neurocranial base, and a single lower pharyngeal jaw. Quantitative cinera-diography revealed that pharyngeal food processing in Oreochromis niloticus involves transport, mastication, and swallowing, effected by cyclical pharyngeal jaw movements. Transport and swallowing occur by simultaneous retractions of both upper pharyngeal jaws. Food reduction (mastication) is effected by lower jaw elevation (compression) and protraction (shear) during upper jaw retraction. Each movement cycle contains a transport, reduction, and swallowing component, although their relative importance may vary within a feeding sequence. The upper and lower pharyngeal jaws show opposite anteroposterior movements during most of the cycle. Variations in the amplitudes and the durations of the different movement components reflect the consistency and the size of the food.     

Morphology of a picky eater: a novel mechanism underlies premaxillary protrusion and retraction within cyprinodontiforms

Upper jaw protrusion is hypothesized to improve feeding performance in teleost fishes by enhancing suction production and stealth of the feeding event. However, many cyprinodontiform fishes (mid-water feeders, such as mosquitofish, killifish, swordtails, mollies and pupfish) use upper jaw protrusion for "picking" prey out of the water column or off the substrate; this feeding mode may require improved jaw dexterity, but does not necessarily require increased stealth and/or suction production. We describe functional aspects of the bones, muscles and ligaments of the anterior jaws in three cyprinodontiform genera: Fundulus (Fundulidae), Gambusia and Poecilia (Poeciliidae). All three genera possess a premaxillomandibular ligament that connects the premaxilla of the upper jaw to the mandible. The architecture of this ligament is markedly different from the upper-lower jaw connections previously described for basal atherinomorphs or other teleosts, and this loose ligamentous connection allows for more pronounced premaxillary protrusion in this group relative to closely related outgroup taxa. Within poeciliids, a novel insertion of the second division of the adductor mandibulae (A2) onto the premaxilla has also evolved, which allows this jaw adductor to actively retract the premaxilla during mouth closing. This movement is in contrast with most other teleosts, where the upper jaw is retracted passively via pressure applied by the adduction of the lower jaw. We postulate that this mechanism of premaxillary protrusion mediates the cyprinodontiforms' ability to selectively pick specific food items from the water column, surface or bottom, as a picking-based feeding mechanism requires controlled and coordinated "forceps-like" movements of the upper and lower jaws. This mechanism is further refined in some poeciliids, where direct muscular control of the premaxillae may facilitate picking and/or scraping material from the substrate.     

Extent and location of bone loss at dental implants in patients with peri-implantitis

Peri-implantitis is an infectious disease, which leads to loss of supporting bone around dental implants. To evaluate the extent and location of bone loss, 43 patients with peri-implantitis were examined. The bone loss was clinically measured at the time of dental surgery. Data revealed that 25% of subjects had bone loss associated with all their implants although the majority of the subjects had fewer than 50% of their implants affected by bone loss. A total number of 264 implants were examined and 131 of those had peri-implantitis associated bone loss. The pattern of bone loss at implants varied between and within subjects and location in the jaws. The highest proportion of implants with peri-implantitis was found in the upper jaw and within this group, at implants located in the incisor area of the upper jaw; the lowest was the canine area of the lower jaw. The highest proportion of implants that lost ≥ 2/3 of their bone support was found in the incisor area of the maxilla. We concluded that in the presence of peri-implant inflammation, bone quantity and characteristics may influence the progression of peri-implantitis bone loss at dental implants. We hypothesize that the ability of the bone to withstand occlusal forces will be altered as consequence of the loss of bone at the neck of the implants. To achieve an understanding of the local degradation of bone due to peri-implantitis, we need to analyze the microstructure of the bone as well the cellular biology of the peri-implant inflammation.     

Chondrocranium morphology of northern Red Sea triakid sharks and relationships to feeding habits

The structure of the neurocranium, mandibular arch and hyoid arch of I. omanensis (Norman) and M. mosis Hemprich & Ehrenberg is described. Comparisons between these species and other triakids and between triakids and carcharhinoids are given. Differences in the size, weight and structure of the mandibular arch, including its associated ligaments and jaw suspension, are shown to be related to feeding habits. Dental characters for both species are examined and differences are considered in relation to diet. Structural elaborations of the nasal capsules in I. omanensis are described in relation to protrusion of the upper jaw during biting. Comparable neurocranial features are poorly developed in M. mosis where the upper jaw shows little discernable anterior movement. The optic region is enlarged in both species in relation to nasal and otic areas of the neurocranium.     

Interaction between Foxc1 and Fgf8 during Mammalian Jaw Patterning and in the Pathogenesis of Syngnathia

Syngnathia (bony fusion of the upper and lower jaw) is a rare human congenital condition, with fewer than sixty cases reported in the literature. Syngnathia typically presents as part of a complex syndrome comprising widespread oral and maxillofacial anomalies, but it can also occur in isolation. Most cartilage, bone, and connective tissue of the head and face is derived from neural crest cells. Hence, congenital craniofacial anomalies are often attributed to defects in neural crest cell formation, survival, migration, or differentiation. The etiology and pathogenesis of syngnathia however remains unknown. Here, we report that Foxc1 null embryos display bony syngnathia together with defects in maxillary and mandibular structures, and agenesis of the temporomandibular joint (TMJ). In the absence of Foxc1, neural crest cell derived osteogenic patterning is affected, as osteoblasts develop ectopically in the maxillary prominence and fuse with the dentary bone. Furthermore, we observed that the craniofacial musculature is also perturbed in Foxc1 null mice, which highlights the complex tissue interactions required for proper jaw development. We present evidence that Foxc1 and Fgf8 genetically interact and that Fgf8 dosage is associated with variation in the syngnathic phenotype. Together our data demonstrates that Foxc1 – Fgf8 signaling regulates mammalian jaw patterning and provides a mechanistic basis for the pathogenesis of syngnathia. Furthermore, our work provides a framework for understanding jaw patterning and the etiology of other congenital craniofacial anomalies, including temporomandibular joint agenesis.     

Comparative kinematics of cypriniform premaxillary protrusion

Premaxillary protrusion has evolved multiple times within teleosts, and has been implicated as contributing to the evolutionary success of clades bearing this adaptation. Cypriniform fishes protrude the jaws via the kinethmoid, a median sesamoid bone that is a synapomorphy for the order. Using five cypriniform species, we provide the first comparative kinematic study of jaw protrusion in this speciose order. Our goals were to compare jaw protrusion in cypriniforms to that in other clades that independently evolved upper jaw protrusion, assess the variation in feeding kinematics among members of the order, and test if variation in the shape of the kinethmoid has an effect on either jaw kinematics or the degree of suction or ram used during a feeding event. We also examined the coordination in the relative timings of upper and lower jaw movements to gain insight on the cypriniform protrusile mechanism. Overall, speed of protrusion in cypriniforms is slower than in other teleosts. Protrusion speed differed significantly among cypriniforms but this is likely not due to kinethmoid shape alone; rather, it may be a result of both kinethmoid shape and branching patterns of the A1 division of the adductor mandibulae. In the benthic cypriniforms investigated here, upper jaw protrusion contributed up to 60% of overall ram of the strikes and interestingly, these species also produced the most suction. There is relatively little coordination of upper and lower jaw movements in cypriniforms, suggesting that previous hypotheses of premaxillary protrusion via lower jaw depression are not supported within Cypriniformes. Significant variation in kinematics suggests that cypriniforms may have the ability to modulate feeding, which could be an advantage if presented with the challenge of feeding on different types of prey.     

Record of an Indo-Pacific humpback dolphin (Sousa chinensis) without its upper rostrum in Xiamen Bay,Fujian Province,China

Many cetaceans are killed as a result of intensive anthropogenic impacts, and those that survive often endure wounds or scars. This study is the first report of an Indo-Pacific humpback dolphin (Sousa chinensis) that is missing its upper rostrum. This individual has inhabited Xiamen Bay, Fujian Province, China, for more than 3 years. Since the lower jaw and the other part around the upper jaw are intact, it is likely that the upper jaw was entangled in fishing nets or pipelines and subsequently broke off. Without the upper rostrum, this dolphin cannot snap prey, but it may use other feeding strategies – and the fact that this individual has survived for more than 3 years without its upper rostrum provides a novel insight into the ability of this species to persist in the wild.     

广东三水盆地的哺乳动物化石

在广东三水盆地新村水库附近的第三系中发现了一哺乳动物的下颌骨和上臼齿。其形态特征很象叉齿兽（Hypsilolambda）,但尺寸比已知的种大很多。它可能代表叉齿兽的一新种,或新属。现暂将其归入叉齿兽属。其产出地层心群一组的时代可能为古新世。     

Sexual dimorphism of skull shape in a lacertid lizard species (Podarcis spp., Dalmatolacerta sp., Dinarolacerta sp.) revealed by geometric morphometrics

Geometric morphometric techniques were used to examine allometric and non-allometric influences on sexual shape dimorphism (SShD) in the ventral cranium (skull base, palate and upper jaw) of four species of lacertid lizards (Podarcis muralis, Podarcis melisellensis, Dalmatolacerta oxycephala, Dinarolacerta mosorensis). These species differ in body shape, ecology and degree of phylogenetic relatedness. The structures of the ventral cranium that were studied are directly involved in the mechanics of feeding and are connected to the jaw musculature; these structures are potentially subject to both sexual and natural selection. Allometry accounted for a considerable degree of cranial shape variation between the sexes. Allometric shape changes between individuals with smaller cranium size and individuals with larger cranium size are mostly related to changes in the skull base showing pronounced negative allometry. The rostral part, however, either scaled isometrically or showed less pronounced negative allometry than the skull base. Non-allometric intersexual shape variation predominantly involved changes related to the jaw adductor muscle chamber, i.e., changes that are associated with biomechanically relevant traits of the jaw system in females and males. Both allometric and non-allometric shape changes appeared to be species-specific. Our results indicate that natural and sexual selection may be involved in the evolution of SShD.     

Upper jaw in human cyclopia

In human cyclopia the upper jaw forms a solid bony mass between the median orbit and the oral cavity. The skeletal elements forming the upper jaw have been studied in serial sections through the median third of the head in 3 perinatal human specimens presenting with a median orbit and proboscis. One head was sectioned in the sagittal plane and 2 in the coronal plane. The upper jaw has also been studied in a dried cyclops skull and in a desiccated cyclops head in which the roof of the orbit had been removed. The data obtained demonstrate the particular contributions made by the lacrimal bones, the maxillae and the palatine bones to the upper jaw in human cyclopia. The effects of the absence of the frontonasal process contribution and of the absence of the nasal cavity on the upper jaw in cyclopia are considered.     

Notes on the typology of the skull of the Myrmecophagidae (Mammalia, Edentata)

The skulls of Myrmecophaga, Tamandua, and Cyclopes are klinorhynch; the upper jaw is situated rostral to the neurocranium and to a varying degree ventral to the plane of the median basis cranii. The median part of the base of the neurocranium is the structure to which the anatomical modifications in the median plane are referred. The kyphosis, which determines the situation of the upper jaw, is prebasically located either within the upper jaw (Myrmecophaga, Tamandua) or at its basis (Cyclopes).     

On the structural adaptations of the bill, skull-elements, tongue, and hyoid of some Indian insect-eating birds

The study of the functional morphology of the feeding apparatus of some Indian insect-eating birds reveals suitable adaptational changes in the structure of their bill, skull-elements, tongue, and byoid in different degrees, depending on the nature of their partial adaptation to secondary food-habits. The hooked tip of the upper beak in Muscicapa and Dicrurus, sharp tomial edges of both the beaks in Turdoides and the long, gradually curved bill in Merops are some of the suitable adaptations of the bill for food-getting. The dimensional variations of the skull and its kinetic elements may be correlated not only with the food-habits of birds studied, but also with the patterns of jaw and tongue muscles possessed by them. A comparatively greater width of the cranium and height of the lower jaw in Turdoides and Dicrurus provide wider areas for the origins and insertions of the adductor muscles. The skull in all the birds studied is pro-kinetic. The kinesis of the upper jaw, however, depends on several factors of which the angles of placement of the quadrate-pterygoid-palatine components, the nature of the naso-frontal hinge and the resultant "torques" produced by differential forces of muscles are very significant. The upper jaw kinesis is best developed in Merops and Orthotomus. The variations in the structure of the tongue and hyoid may also be correlated with various movements of the tongue in both primary and secondary food-adaptations.     

Evolutionary innovation in the vertebrate jaw: A derived morphology in anuran tadpoles and its possible developmental origin

The mouthparts of anuran tadpoles are highly derived compared to those of caecilians or salamanders. The suprarostral cartilages support the tadpole's upper beak; the infrarostral cartilages support the lower beak. Both supra- and infrarostral cartilages are absent in other vertebrates. These differences reflect the evolutionary origin of a derived feeding mode in anuran tadpoles. We suggest that these unique cartilages stem from the evolution of new articulations within preexisting cartilages, rather than novel cartilage condensations. We propose testing this hypothesis through a search for similarities in the development of the suprarostral and infrarostral cartilage articulations and of the primary jaw joint. In Xenopus, the gene zax is expressed in a region corresponding to the infrarostral cartilage. This gene is related to the bapx1-gene, which regulates jaw joint development. Further investigation of these genes, as well as other genes with joint-related functions, in anuran craniofacial development may provide a connection between the morphological diversity seen in the vertebrate head and the corresponding diversity in genetic regulatory processes. We believe that the evolution of larval jaws in anurans may shed light on the general evolutionary mechanisms of how new articulations, not only in the jaw region, could have arisen in the vertebrate skull.     

Nectarivorous feeding mechanisms in bats

Cranio-dental characteristics are quantified between micro- and megachiropteran nectarivores and compared with microchiropteran animalivores, frugivores, and megachiropteran frugivores. Microchiropteran nectarivores share many characteristics with megachiropteran nectarivores and frugivores, but differ in having a long, narrow head. Megachiropterans have wide zygomata, which would allow for more jaw musculature. Diminutive cheekteeth are characteristic of nectarivory in both suborders, but both have relatively large canines. Teeth in nectarivores can occupy as little as a tenth of the palatal area compared to nearly two-thirds in microchiropteran animalivores. The proportion that the dilambdodont stylar shelf occupies of molars in microchiropteran nectarivores can be as much as that in microchiropteran animalivores (insectivorous and carnivorous bats) or as little as that in microchiropteran frugivores but not as extreme as either. In addition to dimunitive teeth, nectarivores have fused mandibles and upper canines that are worn from contact with the lower canines (thegosis). These characteristics may be necessary for the lower jaw to support an elongated, mobile tongue. While microchiropteran nectarivory, frugivory, and carnivory probably evolved independently from an insectivorous microchiropteran ancestor, megachiropteran nectarivory probably evolved from megachiropteran frugivory or the reverse.     

Sexual dimorphism inSebastes

Synopsis Sexual dimorphism and factors that may cause it were investigated in 34 species of the genusSebastes. Sexual dimorphism in standard length and morphometric characters are fairly common in rockfish. In many species males are shorter than females. However in males head length, width of orbit, interorbital width, length of upper jaw, longest pectoral fin ray and longest dorsal spine tend to be larger at a specified size than in females. Water-column species tend to be more dimorphic than demersal species. We suggest that the observed differences in dimorphism in standard length may be related to differences in mating and territorial behavior. Dimorphisms in morphometric measurements may be related to compensation in feeding ability for reduced standard length of males, mating and territorial behavior.     

Jaw protrusion,an optimization of the feeding apparatus of teleosts?

A comparison of nineteen taxa of teleost fishes suggests the gradual acquisition of systems of upper jaw protrusion in the course of fish evolution. However, in view of the loss of protrusion in several groups of advanced teleosts the biomechanicsof protrusile jaws are analysed based on the hydrodynamics of suction feeding. Calculations show that protrusion may reduce the energy otherwise spent in a feeding act to get the predator's mouth as near to the prey in the same time with about 80%. Other generalized advantages and disadvantages of upper jaw protrusion are explained. Detailed ecological data to calculate the balance between pros and cons of jaw protrusion of a particular species in its habitat are still lacking. There is no incompatibility between presence and disappearance of protrusile jaws in fish and current neo-darwinistic theories of evolution.     

The comparative feeding mechanism of gadidae and macrouridae. I. Functional morphology of the feeding apparatus

The comparative feeding apparatus of Gadidae and Macrouridae has been studied from a functional point of view. Some important modifications in macrourid species in comparison with the gadid ones were found: rostral end of the cranium, rostral ligaments and disposition of the jaw muscles. Anyways, all the modifications seem secondary, motivated by the habitat. That is true in the case of the beak, in relation with the swimming system which had been already observed by Marshall and Bourne (1964). The question of the rostral ligaments modification would be related with the protraction of the upper jaw, but a further analysis is required. Also discussed are two schemes of possible changes in the jaw musculature.