Biomechanical interpretation of the early hominid hip

A new pelvic fragment from Swartkrans provides the opportunity to analyze the hip joint mechanics of the robust form of early hominid. The function of the lateral support system provided by the abductor muscles of the hip appears to be similar to that of the gracile early hominid from Sterkfontein. The system is well adapted for providing the lateral support necessary for efficient bipedalism. The hip extensor mechanism and hip internal rotatory system also appear to be well adapted for efficient bipedalism in a way very similar to the other early hominids. The conclusion reached is that the robust and gracile forms of South African early hominids were basically similar in their locomotor adaptation and were most likely habitual bipeds.     

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.     

Ecological and evolutionary consequences of the trophic polymorphism in Cichlasoma citrinellum (Pisces: Cichlidae)

The neotropical cichlid fish Cichlasoma citrinellum is polymorphic in the structure of its pharyngeal jaw apparatus and external morphology. The pharyngeal jaws are either gracile and bear slender, pointed teeth (papilliform) or robust with strong, rounded teeth (molariform). Molariform morphs have a ‘benthic’, and papilliform morphs a ‘limnetic’ body form. Furthermore, this species is also polychromatic, with yellow and black morphs. The molariform morphology of the pharyngeal jaw apparatus adapts the fish for cracking and feeding on snails. Based on analysis of stomach contents, 94% of the molariform morph ate snails whereas only 19%, of the papilliform morph did so. This result suggests that the morphs occupy different ecological niches. The morphology of the pharyngeal jaw apparatus does not correlate significantly with sex, but it does with body colouration (P<0.005). Cichlasoma citrinellum mate assortatively with their own colour; therefore a mating preference for colour may lead to genetic isolation of trophic morphs. The frequency of the molariform morph differs strikingly among populations of five Nicaraguan lakes and its abundance is correlated with the abundance of snails, the fishes' principal prey item. Among populations the frequency of molariform morphs decreases in the dry season. Morphology possibly changes reversibly within particular individuals between seasons. These results suggest that phenotypic plasticity and polymorphisms may be an adaptive characteristic of cichlid fishes. Patterns of intraspecific morphological variation match patterns of interspecific morphological diversification which suggests that universal developmental mechanisms canalize the possible expressions of morphology. The ability to respond morphologically to environmental shifts, in conjunction with genetically determined trophic polymorphisms and sexual selection via mate choice, could be the basis for speciation through intermediate stages of polymorphism of the impressive adaptive radiation of cichlid fishes.     

Arch form,tooth size,and occlusomandibular kinesis in the Ceboidea

Correlations between dental morphology, arch configuration, and jaw movement patterns were quantitatively investigated in 23 ceboid species to elucidate integrative aspects of occlusal functional anatomy in an adaptive and evolutionary context. Differential maxillary-mandibular arch widths are primary in guiding lateral jaw movements. These movements are characterized according to their associated condylar shifts as either predominantly translatory or rotational. Predominantly translatory movements result from peripheral contact relationships between maxillary arches which are considerably wider posteriorly than their opposing mandibular arches. The greatest degree of mandibular movement is in the molar region in functional association with wide “primitive” maxillary molars, narrow mandibular molars, constricted maxillary intercanine widths, and narrow maxillary incisors. In contrast, predominantly rotational masticatory jaw movements result from differential arch widths which are greatest in the maxillary canine and incisor regions. Here most jaw movement is in the anterior segment and this is reflected in small maxillary-mandibular molar width differences, a high degree of premolarization, wide-set maxillary canine teeth, and wide maxillary incisors. Possible selectional factors in the putative evolution of rotational predominance in mastication from the more primitive translatory pattern are discussed.     

Helicoidal plane of dental occlusion

A helicoidal plane of postcanine occlusion has been patchily reported in many recent and fossil dentitions of man, and has been suggested as a taxonomic marker distinguishing between the dentitions of Homo and Australopithecines. The present paper describes the helicoidal plane in 19 out of 23 modern human (probably Indian) worn dentitions, in both gracile and robust Australopithecines and in extant anthropoids. It is suggested that tooth wear converts the plane of occlusion present in little-worn teeth, the Monson curve, into a helicoidal plane when 1) the diet is more abrasive, 2) the enamel is thinner and less abrasion resistant, and 3) a longer time separates the eruption of the three molar teeth in a jaw quadrant. A model demonstrates that during the power stroke of a chewing cycle the working side molars move in much the same direction whether the molar occlusal plan follows a Monson curve or a helicoidal plane. The difference is that in the former case the three molars work at the same time while in the latter case they work in sequence from anterior to posterior, thereby concentrating force on one tooth at a time. Because the occlusal plane changes during the life of individuals consuming an abrasive diet, the condition of most anthropoids and hominids, it is argued that the Monson curve has functional significance not because of its influence on occlusal relations and/or jaw movement but because the molar teeth are embedded in bone roughly perpendicular to it, a direction which resists tilting of the teeth during mastication. It is concluded that the helicoidal plane probably has little if any value as a taxonomic marker.     

Ultrastructure of the mouth apparatus in Branchiobdella pentodonta (annelida,clitellata)

The mouth apparatus in Branchiobdella pentodonta was studied by electron microscopy. The opening is situated dorsal to the adhesive disk of the anterior sucker and is surrounded by a ring of 16 papillae. The papillae have mono-layered epithelium, muscle fibers, glandular processes, and taste and olfactory organs like “sensitive buttons.” The oral cavity contains jaws with horny teeth and “sensitive buttons,” and is surrounded by a ring of circular muscle fibers that connect to the muscle fiber of the papillae. This apparatus shows some analogies to that of Hirudinea, such as the presence of sucker and jaws with horny teeth.     

Phylogenetic aspects of tooth and jaw structure of the Medaka, Oryzias latipes, and other beloniform fishes

Tooth structure is described for adult male, female, and juvenile Oryzias latipes (Temminck & Schlegel), the Medaka. Adult males have enlarged, unicuspid teeth posteriorly on the premaxilla and dentary. Oral teeth are smaller and more numerous in females, in which no tooth is notably larger than the others. Juveniles have numerous small teeth from about 3 mm SL (standard length) onwards. By about 16 mm SL, males begin to develop the large posterior teeth, as well as other secondary sexual characters. Lower and upper pharyngeal teeth of both males and females are fine, and in numerous even rows.
The large, posterior oral teeth of males are fully-ankylosed to the attachment bone, and, hence, are not depressible. In female Medaka, as in the Halfbeak Dermogenys pusillus van Hasselt, the oral teeth have a ring of unmineralized collagen at the base, and are not depressible. Pharyngeal teeth of Medaka have a ring of unmineralized collagen at the base, and a distinct wedge of collagen absent posteriorly, such that the pharyngeal teeth may be depressed.
Bone in adult Medaka is acellular. Incompletely mineralized teeth, acellular bone, a protrus-ible upper oral jaw, and a mobile branchial apparatus with an interhyal bone, form a complex characteristic of advanced teleosts. The Medaka differs in several ways from the model advanced teleost: absence of an interhyal bone, ascending and articular processes of the premaxilla, and the rostral cartilage, as well as presence of cartilaginous symphyses between the dentaries and premaxillae, all contribute to the fixed or nonprotrusible jaws.
Reduction in the premaxilla is a derived character within beloniform fishes for which an enlarged, beaked outer jaw is considered plesiomorphic.     

Innervation of the human upper primary dentition: Implications for understanding tooth initiation and rethinking growth and eruption patterns

Recent comparisons of humans with apes and early fossil hominids have prompted renewed interest in the study of sequences of dental growth and development. Such comparisons, however, rely on certain assumptions about tooth development and dental homology and the biological reality of distinguishing “deciduous” from “permanent” teeth. In light of earlier suggestions by Schwartz that there might be a correlation between nerves and the stem progenitors of tooth classes, and thus between nerve branch number and number of tooth classes, we studied a large sample of ～ 3 month fetuses to elucidate the nature of nerve branching patterns and the development of the primary dentition (i.e., the “deciduous” incisors, canine, and molars, and the first “permanent” molar). Contrary to expectation, variation in nerve branch patterning was the rule. If nerve fibers do have a role in tooth development, it can only be at the time of initiation, with definitive innervation occurring late in tooth development. In taking into consideration the entire span of tooth development—from initiation to innervation to eruption—and the process by which successional teeth arise (each from the external dental epithelium of a predecessor tooth), we suggest that dividing tooth growth and eruption into patterns of the “deciduous” teeth vs. those of the “permanent” is artificial and that a more meaningful approach would be the study of the entire dentition.     

The pharyngeal jaw apparatus of labrid fishes: A functional morphological perspective

Among the acanthopterygian fishes, the Labridae possess the most highly integrated and specialized pharyngeal jaw apparatus. The integrated feature involves many osteological components and aspects of muscle form, architecture, composition, and function. The upper jaw articulates by means of a true diarthrosis with the pharyngeal process of the parasphenoid, whereas the lower jaw has established physical contact with the cleithrum. Complex muscle fusions have contributed significantly in the development of a double muscle sling operating the lower jaw. The original levator externus 4 fuses with the central head of the obliquus posterior, whereas the original levator posterior combines with the lateral head of the obliquus posterior as well as with the adductor branchialis 5. During the masticatory cycle, both upper and lower jaws undergo complex movement orbits resulting in shearing and crushing functions. Shearing occurs as the forward moving upper jaw collides with the dorsally held lower jaw. Crushing is effected by an extreme posterodorsal movement of the lower jaw against the retracted upper jaw, thereby establishing full occlusion of the teeth. The specialized morphological and functional design of the labrid pharyngeal jaw apparatus is similar to that found in cichlids. In sharp contrast to primitive acanthopterygian fishes, the Labridae and Cichlidae exhibit a spectacular morphological diversity that parallels their ecological diversification. Our combined functional and historical analysis has established a correlation between the complex integration of the pharyngeal jaw apparatus and morphological and ecological diversity in the Labridae and Cichlidae.     

Colony Structure in Flustra foliacea (Linnaeus) (Bryozoa,Chéilostomata)

Encrusting forms presumably represent the original mode of growth in the bryozoans. They usually exhibit a relatively low degree of colony integration. The numerous different erect colony types, certainly independently derived from this stage, show a higher degree of integration. Eventually forms arise with a strict pattern only little influenced by the environment. The Flustra foliacea colony holds an intermediate position in this respect. It forms an initial crust on a foreign substratum such as rock. The crust forms marginal lobes. The lobes collide two and two. The two components of each collision then rise back to back, owing to lack of space, into bilaminar fronds. The two zooid layers composing these erect branches and mutually encrusting the “auto-substratum” of their respective basal walls, grow much more rapidly than the initial crust on the “heterosubstratum” of the rock to finally comprise more than 95 % of the colony volume. The different rate of growth on “auto-” and “heterosubstratum” respectively is interpreted as indicating a preference for the “autosubstratum” and as the main force in the formation of erect branches. The Fl. foliacea case indicates one of the pathways from encrusting to erect colonies in the bryozoans. It is probably valid for at least some of the erect bilaminar colonies appearing in different parts of the bryozoan system.     

Aspects of the structure and functional anatomy of the Middle Triassic cynodont Luangwa

The study concerns an incomplete skull and postcranial skeleton of the traversodontid cynodont Luangwa drysdalli Brink, from the Middle Triassic Ntawere Formation of Zambia. The incisor teeth had cutting edges maintained by tooth abrasion, and the post-canines functioned more by a puncture-crushing mechanism than by shearing. The jaw muscles, in conjunction with the teeth, were arranged to avoid stresses at the jaw articulation.
Both the region of the orbit, and the braincase show certain tendencies towards mammalian structure.
The forelimb operated in a primitive, sprawling fashion. The equivalent of the therian supraspinatus muscle had evolved, but not the infraspinatus. The hindlimb was more or less erect, and the hip musculature was very close to mammalian. Expanded costal plates were still present on the posterior thoracic and lumbar ribs, and functioned to maintain the vertebral column virtually rigid.     

腊玛古猿和西瓦古猿的形态特征及其系统关系——颅骨的形态与比较

本文通过具体的形态比较指出,禄丰腊玛古猿和西瓦古猿应为同一类型的雌雄个体,它们与现代猩猩比较相似,而与大猩猩和黑猩猩差别较大,因此,它们可看作是猩猩的祖先。猩猩这一支大约是在一千二百万年前开始从人猿超科的进化主干上分化出来的。     

Intraoral approach for reduction malarplasty: a simple method

Young Korean women with prominent zygoma may experience stress in daily life because the Oriental physiognomy often associates prominent zygoma with bad luck. Moreover, prominent zygoma in a wide Oriental face has the effect of making a person appear older and stubborn. Zygomatic reduction is often necessary to relieve stress from self-consciousness about facial appearance and to obtain younger and softer features. As such, most zygomatic procedures are cosmetic; therefore, an entirely intraoral approach with no skin incision is desirable. The current operative method of zygomatic reduction consists of two steps. The zygomatic body and arch are exposed through a mucoperiosteal incision from the maxillary canine to the first molar area. The first step is to grind and file the zygomatic body. The second step is made on the zygomatic arch. Using an oscillating saw, a partial-thickness osteotomy is made just posterior to the orbital rim, and a full-thickness osteotomy is made just anterior to the articular tubercle of the zygomatic arch. Light pressure on the posterior part of the arch produces a greenstick fracture of the anterior osteotomy site and a complete fracture of the posterior osteotomy site, resulting in inward repositioning of the zygomatic arch. This method of zygomatic reduction is simple, easy, effective, and leaves no conspicuous scars on the face.     

Interspecific and intraspecific relationships between tooth size and jaw size in primates

The association between mandibular robusticity, postcanine megadontia, and canine reduction in hominins has led to speculation that large and robust jaws might be required to spatially accommodate large canine and molar teeth in hominins and other primates. If so, then variations in mandibular form that are generally regarded as biomechanical adaptations to masticatory demands might instead be incidental effects of functional requirements of tooth support. While the association between large teeth and deep, robust jaws in hominins is well known, the relationship between tooth size and jaw size has not been systematically evaluated in a comparative sample of primates. We evaluate the relationships between molar tooth size, canine tooth size, and mandibular corpus and symphyseal dimensions in a sample of adult anthropoids in interspecific (n=84 species) and intraspecific (n=36 species) contexts. For intraspecific comparisons, tooth size and jaw size are correlated, but for a majority of species this is a function of sexual size dimorphism. Interspecific comparisons lend little direct support to the hypothesis that jaw breadth directly covaries with molar tooth breadth, but they do support the hypothesis that mandibular depth is associated with canine tooth size in males. The latter observation suggests that if there is a causal association between canine size and mandibular depth, it is subject to a threshold effect. In contrast, neither corpus nor symphyseal robusticity, measured as a shape index of breadth/height, are correlated with tooth size. Our results suggest that further studies of the relationship between tooth size and corpus morphology should focus on tooth root size and corpus bony architecture, and that species-specific factors should have a strong impact on such relationships.     

Is the deciduous/permanent molar enamel thickness ratio a taxon-specific indicator in extant and extinct hominids?

In Primates, enamel thickness variation stems from an evolutionary interplay between functional/adaptive constraints (ecology) and the strict control mechanisms of the morphogenetic program. Most studies on primate enamel thickness have primarily considered the permanent teeth, while the extent of covariation in tooth enamel thickness distribution between deciduous and permanent counterparts remains poorly investigated. In this test study on nine extant and fossil hominids we investigated the degree of covariation in enamel proportions between 25 pairs of mandibular dm2 and M1 by a so-called “lateral enamel thickness diphyodontic index”. The results did not provide an unambiguous picture, but rather suggest complex patterns likely resulting from the influence of many interactive factors. Future research should test the congruence of the “diphyodontic signal” between the anterior and the postcanine dentition, as well as between enamel and the enamel-dentine junction topography.     

Scanning microscopy of pharyngeal and oral teeth of the teleost Tilapia mossambica (Peters)

The pharyngeal and oral teeth of the fish Tilapia mossambica (Peters) were examined with a scanning microscope. It appeared that the dorsal pharyngeal teeth form a peculiar hooklike extension at the tip, whereas the ventral pharyngeal teeth tend to curve in a posterior direction. The two lateral flanges at the tip of the ventral teeth are probably the areas of contact with the dorsal teeth when the latter are pressed down during sound production or feeding. However, the oral teeth develop along a different line. A part from villiform teeth the upper and lower jaws also develop tricuspid and bicuspid oral teeth, with the bicuspids concentrated mainly along the outer edge of the jaw.     

New archosauromorph fragments from the Dockum Group of Texas and assessment of the earliest dinosaurs in North America

Three small and gracile jaw fragments are recovered from the Boren Quarry, one of the lowest fossil quarries of the Upper Triassic Dockum Group of Texas. The specimens are referred to archosauromorphs, where the morphology of the dentary and teeth of two specimens resemble what is observed in basal saurischians. Growing numbers of early dinosaur fossils from the lowest quarries of the Dockum Group of Texas which correspond to the lowermost Norian raises doubts concerning early dinosaur dispersal during the late Carnian-early Norian interval and the first occurrence of North American dinosaurs which might have happened earlier than previously suggested.     

江苏溧阳夏林似剑齿虎一新种

<正> 夏林石灰厂因采石料,裂隙堆积屡见剑齿虎类化石出露。1977年8月,笔者对产地作了短期发掘,在附近采获一颗似剑齿虎下门齿及少许小型食草偶蹄类臼齿碎片。于挖掘期间,学生朱志洪将他所釆一枚完整的似剑齿虎上犬齿化石热诚相赠,盛情可嘉。本文承蒙刘东生教授的支持和指导,深表感谢。保存在南京地质陈列馆的材料,为Homotherium。