Postcanine Teeth Research Articles

A comparative analysis of temporomandibular joint morphology in the African apes

A number of researchers have suggested a functional relationship between dietary variation and temporomandibular joint (TMJ) morphology, yet few studies have evaluated TMJ form in the African apes. In this study, I compare TMJ morphology in adults and during ontogeny in Gorilla ( G.g. beringei, G.g. graueri, and G.g. gorilla) and Pan ( P. paniscus, P. troglodytes troglodytes, P.t. schweinfurthii, and P.t. verus). I test two hypotheses: first, compared to all other African apes, G.g. beringei exhibits TMJ morphologies that would be predicted for a primate that consumes a diet comprised primarily of moderately to very tough, leafy vegetation; and second, all gorillas exhibit the same predicted morphologies compared to Pan. Compared to all adult African apes, G.g. beringei has higher rami and condyles positioned further above the occlusal plane of the mandible, relative to jaw length. Thus, mountain gorillas have the potential to generate relatively more muscle force, more evenly distribute occlusal forces along the postcanine teeth, and generate relatively greater jaw adductor moment. G.g. beringei also exhibits relatively wider mandibular condyles, suggesting these folivorous apes are able to resist relatively greater compressive loads along the lateral and/or medial aspect of the condyle. All gorillas likewise exhibit these same shape differences compared to Pan. These morphological responses are the predicted consequences of intensification of folivory and, as such, provide support for functional hypotheses linking these TMJ morphologies to degree of folivory. The African apes to not, however, demonstrate a systematic pattern of divergence in relative condylar area as a function of intensification of folivory. The ontogenetic trajectories for gorillas are significantly elevated above those of Pan, and to a lesser but still significant degree, mountain gorillas similarly deviate from lowland gorillas ( G.g. gorilla and G.g. graueri). Thus, adult shape differences in ramal and condylar heights do not result from the simple extrapolation of common growth allometries relative to jaw length. As such, they are suggestive of an adaptive shift towards a tougher, more folivorous diet. However, the allometric patterning for condylar area and condylar width does not systematically conform to predictions based on dietary specialization. Thus, while differences in condylar shapes may confer functional advantages both during growth and as adults, there is no evidence to suggest selection for altered condylar proportions, independent of the effects of changes in jaw size.

New material of the earliest hominid from the Upper Miocene of Chad

Discoveries in Chad by the Mission Paleoanthropologique Franco-Tchadienne have substantially changed our understanding of early human evolution in Africa. In particular, the TM 266 locality in the Toros-Menalla fossiliferous area yielded a nearly complete cranium (TM 266-01-60-1), a mandible, and several isolated teeth assigned to Sahelanthropus tchadensis and biochronologically dated to the late Miocene epoch (about 7 million years ago). Despite the relative completeness of the TM 266 cranium, there has been some controversy about its morphology and its status in the hominid clade. Here we describe new dental and mandibular specimens from three Toros-Menalla (Chad) fossiliferous localities (TM 247, TM 266 and TM 292) of the same age. This new material, including a lower canine consistent with a non-honing C/P3 complex, post-canine teeth with primitive root morphology and intermediate radial enamel thickness, is attributed to S. tchadensis. It expands the hypodigm of the species and provides additional anatomical characters that confirm the morphological differences between S. tchadensis and African apes. S. tchadensis presents several key derived features consistent with its position in the hominid clade close to the last common ancestor of chimpanzees and humans.

CRANIAL ANATOMY AND TAXONOMY OF THE LATE PERMIAN DICYNODONT DIICTODON

Reexamination of the cranial anatomy of the abundant Late Permian dicynodont Diictodon confirms suggestions that only one species, D. feliceps, is recognizable. This monotypic genus is highly distinctive, being characterized by such features as a palatal notch, a large dentary table with a medial cutting blade, and the absence of postcanine teeth. Numerous anatomical variations exist within D. feliceps, but many appear biologically insignificant and show no apparent correlation with one another of with locality or stratigraphic position. However, statistical analysis reveals the presence of several features that correlate with the presence of canine tusks, including an occipitally positioned postparietal bone and the presence of a boss surrounding the pineal opening. This suggests that tusked and tuskless specimens do indeed represent distinct biological categories, but it seems highly probable that they are divisions within a single species (most probably opposite sexes) rather than distinct species. It is hoped that the detailed osteological description of the Diictodon skull presented here will provide useful data for future phylogenetic analyses of dicynodonts.

Ontogenetic migration of the mental foramen in Neandertals and modern humans

Since the nineteenth century, researchers have noted that Neandertal and modern human adults differ in mental foramen position, although the ontogenetic changes in the position of this feature have only recently come under the scrutiny of paleoanthropologists. Research on mental foramen position has focused on whether this feature is inferior to a particular tooth. However, tooth position may not be a reliable indicator of mental foramen position because of variability in tooth size within and between taxa and during eruption events. As opposed to observing the mental foramen with respect to the postcanine teeth, we examined linear distances from the mental foramen to other mandibular landmarks. Modern human adults may appear truncated, or paedomorphic, in mental foramen position with respect to Neandertal adults. However, infants of the two taxa differ substantially in anterior mandibular form. The initial differences in the shape of the mental region may be related to the embryological position of the mental foramen in modern humans and its role in the development of the mental trigone. The shape changes that accrue thereafter, possibly from faster mandibular growth rates in Neandertals, further distinguish the adults from one another. Although mandibular shape differences exist from early infancy onwards, adults of the two taxa are broadly similar in bi-mental foramen breadth with respect to mandibular size. For this reason, qualitative assessments of mental foramen position may provide less taxonomic information than previously thought.

Changes in jaw muscles activity with age: effects on food bolus properties

Bolus formation depends on chewing process that evolves with age. This study aims to analyze the effect of age on chewing behavior (recorded by EMG) and the consequences on bolus formation for meat products. Twenty-five young adults (age range: 25–30) and 20 healthy elderly (age range: 68–73) having at least six pairs of natural postcanine teeth participated. From two different textures of bovine meat, boli were characterized by shear force measurements. Saliva incorporated into the bolus was quantified. Chewing duration was significantly longer in the elderly group for both textures, but muscle activity was significantly lower for the toughest texture only. Moreover, muscle activity was less accurately adapted to food texture in elderly than in young. In order to control that changes in EMG reflect changes in bite force, EMG was recorded during static bite forces. Slopes were fairly similar for both groups suggesting that EMG/bite force relationships do not vary with age. Elderly subjects could partly compensate for a weaker chewing efficiency by increasing the number of chewing cycles before swallowing. It is hypothesized that lengthening of chewing duration results from a decrease in muscle activity during healthy aging. After chewing, the mechanical resistance of the bolus was always higher for the elderly than for the young subjects. No significant age effect was found on the amount of saliva incorporated in the bolus. Elderly subjects, despite the lengthening of the chewing sequence, were less efficient to comminute a meat bolus than young subjects and swallowed less comminuted boli.

Ecomorphological indicators of feeding behaviour in the bears (Carnivora: Ursidae)

AbstractPatterns of morphological variation in the skulls of extant bears were studied as they relate to diet and feeding behaviour. Measurements of craniodental features were used to compute indices that reflect dietary adaptations of the dentition and biomechanical properties of the skull, jaw and related musculature. Species were classified as either carnivores, omnivores, herbivores or insectivores. Differences among dietary groups were assessed with analysis of variance and discriminant factor analysis. Results demonstrated significant morphological separation among all four groups. Carnivores were distinguished by, among other features, molar size reduction, flexible mandibles and, most surprisingly, relatively small carnassial blades. In contrast, herbivores displayed, among other features, large molar grinding areas, rigid mandibles and large carnassial blades. The insectivorous sloth bear was characterized by extreme reduction of the post‐canine teeth. As expected, omnivores tended to have morphology intermediate between that of carnivorous and herbivorous ursids. Comparison with previous studies revealed that bears exhibit a different set of morphological specializations for diet than other carnivoran groups. Carnivorous ursids, for example, were found to share aspects of craniodental morphology with omnivorous canids. The relatively weak adaptations for carnivory observed in bears may be the result of selection for the ability to cope with temporal fluctuations in dietary components. The giant panda Ailuropoda melanoleuca was found to have a relatively stiff jaw and great mechanical advantage of the jaw‐closing muscles, features previously observed in carnivorous canids and unexpected in this herbivorous bear. Comparison of patterns of morphological variation and patterns of phylogenetic relationships among species revealed surprisingly strong congruence between morphology and phylogenetics.

A new galesaurid (Therapsida: Cynodontia) from the Lower Triassic of South Africa

A new galesaurid cynodont, Progalesaurus lootsbergensis gen. et sp. nov., is described on the basis of a well‐preserved skull, lower jaw, right scapula and left atlantal neural arch. Autapomorphies of Progalesaurus include postcanine teeth bearing numerous mesial and distal accessory cusps that flank a recurved main cusp, a post‐temporal fenestra bordered by the squamosal ventrally and a large external naris. Progalesaurus is similar to Galesaurus in possessing a poorly defined masseteric fossa on the dentary, a strongly recurved main cusp of the postcanine dentition, an incomplete secondary palate and a similar basisphenoid‐parasphenoid morphology. A cladistic analysis of ten early cynodont genera resolves a monophyletic Galesauridae encompassing Cynosaurus, Progalesaurus and Galesaurus, although support for this clade is weak. Procynosuchus and Dvinia are placed at the base of Cynodontia whereas Thrinaxodon and Platycraniellus are positioned higher, but outside of Eucynodontia. The holotype and only known specimen of Progalesaurus was collected during systematic prospecting of Permo/Triassic boundary strata at New Lootsberg Pass, Graaff‐Reinet District, South Africa. The discovery of Progalesaurus increases the number of valid Early Triassic cynodonts to four and sheds light on the tempo of early cynodont diversification after the end‐Permian mass extinction.

Ageing live New Zealand sea lions (Phocarctos hookeri) using the first post-canine tooth

Live New Zealand sea lions (Phocarctos hookeri) were aged from growth layer groups (GLGs) in the cementum of a lower first post-canine tooth. A single post-canine (PC1) was removed from individuals of known-age (n = 74) between 1997 and 2001 while under a full anaesthetic. Teeth were decalcified, sectioned on a cryostat, stained and then mounted on glass slides. Age was estimated by counting GLGs in the cementum multiple times. Age estimates were calibrated with known-aged individuals and confirmed the annual formation of cementum annuli in PC1 tooth. While there is some variation in assigning exact age to individuals, it was possible to age 94% of teeth to the exact year or to within 1 year of actual age. There was no significant difference in the slope of regression lines associated with actual and estimated age using this technique (t-test, t = 0.309, d.f. = 144, P < 0.05). Accuracy in ageing was improved by discarding sets of readings with low precision and re-reading the tooth until a precise set of estimates was made. GLGs in the cementum were more accurate and robust for age estimation than using GLGs in the dentine. This paper describes a reliable method for the preparation and ageing of the first post-canine tooth (PC1) from live New Zealand sea lions.

New remains of Sphagesaurus huenei (Crocodylomorpha: Mesoeucrocodylia) from the Late Cretaceous of Brazil

ABSTRACT Recent discovery of an almost complete skull of Sphagesaurus huenei, a previously poorly known form from the Late Cretaceous of southern Brazil, shows unexpected morphology for a crocodyliform, including an extreme heterodonty with small lower incisors, large upper caniniforms, and reversed triangle-like postcanines; edentulous anterior region of premaxilla; and maxilla with posterior wall over the anterior margin of the suborbital fenestra. The postcanine teeth have extensive wear facets, implying an alternate unilateral occlusion and suggesting the presence of both lateral and fore-aft movement of the jaw. These characteristics appear unique within the crocodyliform lineage, showing that feeding diversity was wider than thought in this clade. The phylogenetic relationships of Sphagesaurus huenei are evaluated through a parsimony analysis. Sphagesaurus lies within a monophyletic group formed by Cretaceous and Tertiary taxa traditionally referred as notosuchians and sebecosuchians. Interestingly, several mammal-like tooth morphologies were present in this clade of terrestrial crocodyliforms.

A second specimen of Lemurosaurus pricei (Therapsida: Burnetiamorpha)

ABSTRACT A second specimen of the basal therapsid Lemurosaurus pricei preserves aspects of this taxon's cranial anatomy, such as the structure of the temporal region, palate, and lower jaw, that were either unknown or poorly preserved in the holotype. Although typically considered a dinocephalian feature, intermeshing of the incisors is confirmed for Lemurosaurus. Autapomorphies of the genus include a nubbin-like boss at the apex of the lateral temporal fenestra, the presence of very coarse serrations on the posterior margins of the upper postcanine teeth, and the low, ridge-like form of the median frontal crest. The anatomical data provided by the new Lemurosaurus specimen permits the first cladistic appraisal of its phylogenetic position among biarmosuchian therapsids. A cladistic analysis of 10 therapsids, two outgroups, and 38 characters indicates that Lemurosaurus is the sister taxon to a clade including Bullacephalus, Proburnetia, and Burnetia. Taxonomically, this position implies the reclassification of Lemurosaurus as a basal burnetiamorph, rather than as an ictidorhinid. Biogeographically, the position of Lemurosaurus makes it most parsimonious to infer that burnetiamorphs originated in southern Africa, although this hypothesis ignores potential sampling biases.

Masticatory performance with a prosthesis following maxillectomy: an analysis of 43 cases.

To statistically evaluate the factors that influenced masticatory performance following Maxillectomy, masticatory performance was measured in 43 patients with a post-operative prosthesis by means of a spectrophotometer using adenosine triphosphate (ATP) granules. Our statistical analysis revealed that the number of occluding post-canine teeth and the patient's sex were factors that influenced masticatory performance and demonstrated that it was most important to improve occlusion in the pre-molar/molar region.

An enigmatic (Synapsid?) tooth from the Early Cretaceous of New South Wales, Australia

ABSTRACT Largely fragmentary fossils from sites in New South Wales, Victoria, and Queensland, Australia document terrestrial and marine vertebrate faunas of Aptian–Albian age. The natural cast of a large tooth from the Griman Creek Formation, Lightning Ridge, New South Wales, records the presence of a hitherto unknown member of the fauna. Although reference to one of the groups of crocodyliforms that evolved complex, mammal-like postcanine teeth cannot be excluded, the fossil more likely represents a species of synapsid. In some respects it is similar to lower postcanines of traversodontids. Greater morphological similarities to upper molars of dryolestids make reference of this tooth to this group more likely. Current Mesozoic Laurasian and Gondwanan fossil records include mammals with cheek teeth of similar large size.

Sex- and age-related variations in cranial measurements and suture closure in the Australian sea lion, Neophoca cinerea (Peron, 1816)

A total of 65 skulls of the Australian sealion, Neophoca cinerea, was examined to investigate the extent to which sexual dimorphism is reflected in cranial dimensions (n = 32) and skull growth, and to determine whether cranial sutures (n = 18) can be useful in age determination. All adult skull dimensions studied display significant sexual dimorphism. Skull growth ceases close to 4–7 years of age for females (Suture Fusion Rating, SFR 25–34) but skull growth in males continues until at least 16 years of age. In animals with a SFR ≥� 25, male skulls have a minimum condylobasal length of 272 mm, whereas female skulls have a maximum condylobasal length of 259 mm. The relatively early closure of the cranial vault sutures (cessation of brain growth) is balanced by the continued growth of the bony projections that provide muscle attachment (e.g. mastoid width). The later fusion of the snout and palate sutures corresponds with the continued growth of the snout and palate to match the prolonged growth of the mandibles. The upper sixth postcanine tooth was present in 43% of the adult female skulls, but only 15% of the adult male skulls. The data suggest that it may be possible to determine age(s) from examination of the sequence of fusion of cranial sutures as well as by calculation of an overall suture fusion rating for the skull.

Age estimation in crabeater seals (Lobodon carcinophagus)

AbstractThe age of crabeater seals Lobodon carcinophagus was first estimated from the teeth by counting layers in the dentine in transverse sections of the canine teeth. Reliable estimation of age from canine teeth in animals older than c. 10 years is not possible because of root closure at a relatively early age. The present investigation compared various methods of estimating age by examination of tooth sections from a large sample of crabeater seals from Marguerite Bay, Antarctic Peninsula. The most reliable estimations were shown to be obtained by counting layers in the cementum of the third postcanine tooth. Ages of 1233 animals (58% female, 42% male) ranged from 0.5 to 39 years. It is suggested that time‐ and age‐specific historical material is potentially relevant for contemporary growth and life‐history studies as well as for trophic relations or concentrations of pollutants in animal tissues.

A closer look at Neanderthal postcanine dental morphology: The mandibular dentition

Neanderthals are known to exhibit unique incisor morphology as well as enlarged pulp chambers in postcanine teeth (taurodontism). Recent studies suggest that their overall dental pattern (i.e., in morphologic trait frequencies) is also unique. However, what this means in a phylogenetic sense is not known. Although exploring the polarity of dental morphologic characters is essential to understanding the phylogenetic implications of unique patterns of variation, few have undertaken this task. This study moves beyond standard scoring methods, which are based on modern humans, to include several postcanine traits that have not been considered previously. In addition, Homo erectus is used as an outgroup to Neanderthals and modern humans to explore the polarity of these traits. The findings of this study suggest that Neanderthals are not only unique in their pattern of dental trait frequencies (as found in previous studies) but that they present several dental autapomorphies, as well. These include a high frequency of the mid-trigonid crest in lower molars and unique morphology of the lower premolars. Interestingly, these characters are not observed in the Mauer mandible, which some have claimed to be a member of a chronospecies that is a unique ancestor to Neanderthals.

Allometric Scaling in Platyrrhine Molars and Relationships between Their Relative Size and Loss of the Third Molar in the Callitrichinae

There is the hypothesis (Ford, 1980) that the callitrichines, which are rapidly dwarfed, should have relatively large postcanine teeth in comparison with other platyrrhines (non-callitrichines) and the loss of the third molars is probably the result of crowding from the disproportional enlarged molar teeth. In the present study, to test this hypothesis, the allometric relationships between body weight and molar area were analyzed on the basis of species arrangements of recent platyrrhine taxonomy (16 genera and 84 species). The abscissa variable was body weight and ordinate variables were sum of the first and second molar areas and total molar areas in each jaw. After logarithmic transformation of these variables, allometric equations were computed among the callitrichine species (4 genera and 25 species) and among the non-callitrichine platyrrhine species (12 genera and 29 species), respectively. The slopes for the regression lines did not differ between callitrichines and non-callitrichines in each type of molar area. The intercepts were not statistically different between callitrichines and non-callitrichines in sum of the first and second molars, whereas callitrichines were significantly smaller in intercepts for total molar area than non-callitrichines. These results reveal that callitrichines have smaller total molar area relative to body weight than non-callitrichines due to the loss of the third molar. Thus the present study does not support the above-mentioned hypothesis.

Development, Function and Evolution of Teeth

Part I. Genes, Molecules and Tooth Initiation: 1. Homeobox genes in initiation and shape of teeth during development in mammalian embryos Paul T. Sharpe 2. Return of lost structure in the developmental control of tooth shape Jukka Jernvall and Irma Thesleff 3. Molecules implicated in odontoblast terminal differentiation and dentinogenesis J. V. Ruch and H. Lesot 4. Enamel biomineralization: the assembly and disassembly of the protein extracellular organic matrix Alan G. Fincham, Janet Moradian-Oldak, Michael L. Paine, Malcolm L. Snead and Margarita Zeichner-David Part II. Tooth Tissues: Development and Evolution: 5. Evolutionary origins of dentine in the fossil record of early vertebrates: diversity, development and function Moya Smith and Ivan Sansom 6. Pulpo-dentinal interactions in development and repair of dentine Tony Smith 7. Prismless enamel in amniotes: terminology, function and evolution P. Martin Sander 8. Two different strategies in enamel differentiatioerentiation: marsupialia versus eutheria W. von Koenigswald 9. Incremental markings in enamel and dentine: what they can tell us about the way teeth grow M. C. Dean Part III. Evolution of Tooth Shape and Dentition: 10. Evolutionary origins of teeth and jaws: developmental models and phylogenetic patterns M. M. Smith and M. I. Coates 11. Development and evolution of dentition patterns and their genetic basis Z. Zhao, K. M. Weiss and D. W. Stock 12. Evolution of tooth attachment in lower vertebrates to tetrapods P. Gaengler 13. Tooth replacement patterns in non-mammalian vertebrates B. K. Berkovitz 14. The evolution of tooth shape and tooth function in primates P. M. Butler 15. 'Schultz's Rule' and the evolution of tooth emergence and replacement patterns in primates and ungulates B. H. Smith Part IV. Macrostructure and Function: 16. Developmental plasticity in the dentition of a heterodont polyphyodont fish species A. Huysseune 17. Enamel microporosity and its functional implications R. P. Shellis and G. H. Dibdin 18. Pathways to functional differentiation in mammalian enamel J. M. Rensberger 19. Trends in the evolution of molar crown types in ungulate mammals: evidence from the northern hemisphere J. Jernvall, J. P. Hunter and M. Fortelius 20. Function of postcanine tooth crown shape in mammals P. W. Lucas and C. R. Peters 21. Primate dental functional morphology revisited M. F. Teaford Index.

A new family of primitive mammal from the Mesozoic of western Liaoning, China

A fairly well-preserved specimen of a new primitive mammal, Repenomamus robustus gen. et sp. nov., has been described from the Yixian Formation (Lower Cretaceous), western Liaoning, China. This animal has several derived characteristics, such as well-developed den-tary/squamosal articulation, reduced number of tooth, differentiation of premolars and molars in postcanine teeth, presence of a dorsal process of the premaxilla that is not in contact with the nasal, closed medial wall of the orbit, and presence of fingerlike promontorium on the petrosal. It also retains some primitive reptile-like features. It is the most primitive taxon among the three mammals known from the Jehol Biota, and also represents the largest mammal of Mesozoic age over the world.

Dental incremental lines in some small species of the European vespertilionid bats

The dentine and cementum of the mammals exhibit incremental lines (IL) that may be seen as dark and light rings in properly prepared sections of teeth. Counting of IL provides a potential method to evaluate the absolute age of many wild species. The aim of the present study was to evaluate IL in small bat species and to test whether the number of IL is associated with the absolute age of bat when its minimal age was known based on ringing data. Teeth of 26 specimens of the following species were examined:Myotis daubentonii (n = 12),Barbastella barbastellus (n = 4),M. brandtii (n = 2),M. nattereri (n = 2),Pipistrellus nathusii (n = 2),Plecotus auritus (n = 2),M. dasycneme (n = 1),Vespertilio murinus (n = 1). Transverse morphological sections of canines, incisors and postcanine teeth were analysed by a light microscopy. In 4 cases, the minimal age of animals examined in this study was known. The IL were revealed in the dentine of 14 bats examined. The cementum of all animals was devoid of IL. The mean distance between the first and second juxtaposed IL ofM. daubentonii was 3.2 ± 0.2 mm, but it was significantly fewer among the subsequent adjacent lines. Due to a thinness of the IL, an accurate counting was considerably difficult in the canines containing more than 10 IL, as well as in the incisors and postcanine teeth with more than 3-6 IL. The IL of roots showed the most contrast, but they were almost obscured from view at the cingulum and crown. In bats of known-age, the numbers of IL were significantly lower than minimal age of those animals examined, and IL were either revealed only in certain teeth or absent entirely in all teeth. The present findings suggest that the number of the IL varies in different teeth and is strongly dependent on section level. Consequently, age determination in small bats using dental IL is doubtful and requires a reevaluation.

Metrical dental analysis on golden monkey (Rhinopithecus roxellana)

Dental variation in the Chinese golden monkey (Rhinopithecus roxellana) is here evaluated by univariate, bivariate, and multivariate analyses. Allometric analyses indicate that canines and P3s are positively, but other dimensions negatively scaled to mandible and maxilla, and to body size. With the exception of the mesiodistal dimensions of I1 and M3, and the buccolingual dimension of P4, mandibular dental variables show similar scaling relative to body size. Analysis of residuals shows that males have significantly larger canine, P3 and buccolingual dimensions of the postcanine teeth (M2 and M3) than females. A significant difference in shape between the sexes is found in the buccolingual dimension of the upper teeth, but not in the mandible. Unlike the situation in some other species, female golden monkeys do not exhibit relatively larger postcanine teeth than males. In fact, the reverse is true, expecially for M2s and M3s. The fact that most of the dental variables show low negative allometry to body size might be related a cold environment that has led to the development of larger body size with reduced energy loss. When the raw data are examined by Discriminant Function Analysis the sexes are clearly distinguishable.