Sexual dimorphism of cusp dimensions in human maxillary molars

Cusp dimensions of human maxillary molars were compared between males and females to determine whether the later-developed, distal cusps displayed greater sexual dimorphism than the earlier-developed, mesial cusps, and whether the later-forming second molar displayed greater sexual dimorphism than the first molar. First and second permanent molar crowns (M1 and M2) were measured indirectly, using dental casts obtained from 117 Japanese (65 males and 52 females). Measurements included maximum mesiodistal and buccolingual crown diameters and the diameters of the four main cusps: the paracone, protocone, metacone, and hypocone. Mean values of crown dimensions were larger in males than in females for both M1 and M2, but the sexual difference in protocone diameter of M1 was not significant. The protocone in M1 showed the least amount of sexual dimorphism, followed by the metacone, hypocone, and paracone, while in M2, the percentage sexual dimorphism corresponded to the order of cusp formation: paracone, protocone, metacone, and hypocone. With the exception of the paracone diameter, M2 showed greater sexual dimorphism than M1. Sexual dimorphism was not always greater in the later-developed, distal cusps of M1 or M2, but the protocone, the most important cusp in terms of occlusal function, displayed the least dimorphism in M1.     

Genetic correlations between mandibular molar cusp areas in baboons

Primate evolutionary studies rely significantly on dental variation given the large role that teeth play in how an organism interacts with its environment (animal and plant) and conspecifics. Variation in cusp size has been shown to vary among primate taxa, although most studies to date focused on extant and extinct hominoids. Here we test the assumed hypothesis that a significant proportion of this variation in baboons is due to the additive effects of genes. We perform quantitative genetic analyses on variation in two-dimensional (2-D) mandibular molar cusp size in a captive pedigreed breeding population of baboons (Papio hamadryas) from the Southwest National Primate Research Center. These analyses show that variation in cusp size is heritable and sexually dimorphic. Additionally, we tested for genetic correlations between cusps on the same crown, between morphological homologues along the tooth row, and between cusp area and crown buccolingual width. We find that four of the six cusp pairs on the first molar have a genetic correlation of one, save for the metaconid-hypoconid and entoconid-hypoconid, which are not statistically different from zero. The second and third molars have lower genetic correlations, although the metaconid-hypoconid correlation is similarly estimated at zero and the entoconid-protoconid correlation is estimated to be one. This cross pattern of genetic and no genetic correlation does not immediately accord with the known pattern of development and/or calcification. We propose two explanative hypotheses.     

Genetic structure of a tribal population, the Yanomama Indians. XIII. Dental microdifferentiation.

Data are presented on the frequency of the following eight dental traits in 635 Yanomama and 65 Makiritare Indians: upper central incisor rotation or winging, shoveling of maxillary incisors, maxillary molar hypocone reduction, Carabelli's trait, mandibular molar cusp number, mandibular molar cusp pattern rotation of second lower premolar, and pattern of second lower premolar cusps. Yanomama dentition is unusual in the high frequency of six cusps on the mandibular molars. There is marked dental microdifferentiation between villages; significant agreement was observed between a matrix of pairwise "dental distances" based on six morphological traits and corresponding matrices based on 11 genetic systems and on geographic location.     

Associations between Carabelli trait and cusp areas in human permanent maxillary first molars

Few dental anthropological studies have investigated the associations between tooth crown size and crown traits in humans using quantitative methods. We tested several hypotheses about overall crown size, individual cusp areas, and expression of Carabelli cusps in human permanent first molars by obtaining data from standardized occlusal photographs of 308 Australians of European descent (171 males and 137 females). Specifically, we aimed to calculate the areas of the four main molar cusps, and also Carabelli cusp, and to compare the relative variability of cusp areas in relation to timing of development. We also aimed to compare cusp areas between males and females and to describe how Carabelli cusp interacted with other molar cusps. Measurements included maximum crown diameters (mesiodistal and buccolingual crown diameters), the areas of the four main cusps, and the area of Carabelli cusp. The pattern of relative variability in absolute areas of molar cusps corresponded with their order of formation, the first-forming paracone displaying the least variation, and the last-forming Carabelli cusp showing the greatest. Overall crown size and areas of individual cusps all showed sexual dimorphism, with values in males exceeding those in females. Sexual dimorphism was smallest for paracone area and greatest for Carabelli cusp area. Overall crown size and cusp areas were larger in individuals displaying a Carabelli cusp, especially the hypocone area. Although the combined area of the protocone and a Carabelli cusp was greater in cuspal forms than noncuspal forms, protocone area alone was significantly smaller in the former. Our findings lead us to propose that, in individuals with the genotype for Carabelli trait expression, larger molar crowns are more likely to display Carabelli cusps, whereas molars with smaller crowns are more likely to display reduced forms of expression of the trait. We suggest that the pattern of folding of the internal enamel epithelium in developing molar crowns, particularly in the protocone region, can be modified by a developing Carabelli cusp.     

Study of the cuspal ridges of the upper first molars in a modern Japanese population

Materials used were dental casts of the upper first molars of modern Japanese subjects, comprising 29 males and 25 females. Their molar occlusal surfaces were photographed by moiré contourography using the standard trigonal plane. The ridges of a cusp, comprising a central ridge and mesial and distal accessory ridges, were identified from the patterns of the moiré fringes. The central ridge was observed in all cusps except for the hypocone in both sexes. Frequencies of the mesial and distal accessory ridges of trigonal cusps were over 90% except for the distal accessory ridge of the metacone, and those of the hypocone were under 25% in both sexes. These values were generally higher in males than in females, especially for the distal accessory ridge of the metacone. The running pattern of the cuspal ridges showed little difference between sexes. The oblique ridge which was higher than the central groove formed a saddle-like structure. This ridge was observed in all materials, but its heights and structural components varied remarkably. In this study, the distal accessory ridge of the metacone was found to be incorporated into the oblique ridge in about 13% of cases. Variability in the running pattern of the ridges within a single cusp was highest in the hypocone and lowest in both the paracone and protocone. The results obtained are considered to represent the stability or reductive tendency of cusps in the upper first molars.     

Patterns of dental wear and the role of the canine in Cercopithecinae.

The importance of dental wear patterns in understanding masticatory functions in primates has long been appreciated. However, studies of wear patterns among populations of nonhuman primates are few. The purpose of this investigation is to establish the developmental aspects of dental wear in the Cercopithecinae and to describe certain relevant morphological traits. Studies were made of dental casts from 200 primate specimens of Macaca nemestrina, Macaca mulatta, and Papio cynocephalus. These casts were taken at four-month intervals, beginning at two years of age and continuing over a period of six to seven years. The wear pattern starts with the rounding and eventual flattening of the protoconid and protocone of the erupted first molars. Once this stage is reached, the hypoconid and metaconid of the mandibular, and the hypocone and paracone of the maxillary molars are rounded and eventually flattened. This pattern is maintained until the cusp tips are removed and the dentin exposed, however, the entoconid and metacone are not subjected to significant wear at this stage. Analysis of these dental casts and museum specimens has provided data on the development of dental wear during the maturation of these primates. The distribution of forces acting upon the teeth produce diagnostic patterns of wear, which provide evidence of the force location and magnitude. In examining the data, the hypothesis of canine guidance and its limitation of mandibular motion was evaluated. Specimens whose canines were removed demonstrate that the canines play no significant role in the development or maintenance of dental wear planes.     

Ursavus在中国的首次发现——并记禄丰古猿化石产地的其他熊类标本

本文记述的是1981年在禄丰古猿化石产地发掘中发现的熊类标本,共有二属二种和一种暂不能确定属、种的类型。其中祖熊(Ursavus)过去只见于欧洲、北美和西亚的中新世地层,在我国还是首次发现。禄丰的标本,就其大小和特征可归于Ursavus depereti;印度熊(Indarctos)过去在我国发现过两个种:中国印度熊(I.sinensis)和拉氏印度熊(I.lagrelli),禄丰的标本为前一个种;第三类型与Protursus和Ursus都有相似之处,但又有区别,鉴于材料不足,暂不订属和种。     

Cusp size, sexual dimorphism, and heritability of cusp size in twins.

Overall measures of mandibular molars reflect the combined size contributions of the component cusps and ridges. Until now, the size hierarchy of primary and permanent mandibular molar cusps remained unclear. This paper utilizes the relative plane surface areas (basal area dimensions) of the individual molar cusps, as assays of cusp size to demonstrate cusp size variations within populations, antimere cuspal variations, sexual dimorphism, and, the heritability of cusp size. Duplicate dental casts from 199 pairs of like-sexed twins provide the raw dats. Defined anatomic landmarks on the occlusal surfaces were reduced to X-Y rectangular coordinates prior to the computation of the basal areas dimensions. The results establish a cusp size hierarchy specific for molar type, i.e., five-cusped molars with a distal fovea and distal marginal ridge (5fd), five-cusped molars without a distal fovea and without a distal marginal ridge (5o), and four-cusped molars (4c). Sexual dimorphism in cusp size is apparent in 5fd molar cusped but not in 5o molar cusps. However, males have a significantly higher frequency of 5fd molars. Females have a higher frequency of smaller 5o and 4c molars which have fewer crown components. Moreover, female 5o molars have cusps as large as or larger than 5o male molor cusps. Right-side-left-side differences exist between antimere cusps based on relatively low correlations. The mirroring of molor types occurs infrequently. When observed, most intrapair differences for cusp size, using F-ratios, indicate a low component of hereditary variability.     

The relation of canine size to pattern and extent of attrition in baboons

For most genera of animals the association between dental morphology and diet is such that inferences concerning the diet can be made on the basis of the dentition alone. The canine is the one tooth that appears exempt from such generalisation and exhibits a wide range of variability of size and shape in all groups. In order to determine the effect of dimorphism of the canine on the dental apparatus, male and female specimens of Theropithecus and Papio baboons were examined. Occlusal relationships and dental pathology for 21 Theropithecus and 40 Papio skulls were recorded, and crown height measurements obtained for maxillary incisors, buccal and lingual molar cusps. Attrition was the most common and severe cause of abscess formation in older animals: the pattern of attrition differed in adult males and females, the latter showing more wear of the incisor and lingual molar cusps. Partial correlations for incisor, buccal and lingual molar cuspal crown height show a significant correlation between incisor and lingual cusp attrition in juveniles of both sexes and adult females (p < 0.01). Adult males show no correlation of attrition. It is proposed that the correlation of incisor and lingual molar cusp attrition is associated with anterior-posterior grinding movements, such as take place during incision, that the large canine present in the male limits such movements, the sharp blade-like canine being employed as a cutting tool. This use of the canine by reducing functional demands on other teeth, prolongs the utility of the dental apparatus, and hence the lifespan of its possessor.     

Dentition and Jaw of Kokopellia juddi, a Primitive Marsupial or Near-Marsupial from the Medial Cretaceous of Utah

We add to the knowledge of the dentition and lower jaw of the primitive marsupial or near marsupial, Kokopellia juddi, based on newly collected materials from the medial Cretaceous (Albian–Cenomanian) of central Utah. The dental formula, i4 c1 p3 m4, is primitive for (or with respect to) Marsupialia, as are a number of features of the dentary and dentition: presence of a labial mandibular foramen, ?an inflected angle, ?and a trace of the meckelian groove; lack of “staggering” of the lower incisor series; lack of “twinning” between entoconid and hypoconulid on lower molars; incompletely lingual position of lower molar paraconid; upper molar protocone relatively small and mesiodistally narrow; and conules placed about halfway between the protocone and the paracone–metacone. Other than the stylocone, cusps are lacking from the stylar shelf; we argue that this represents the primitive marsupial condition based on the economy of character change and the stratigraphic record of marsupials in the Cretaceous of North America. Recent discoveries of early marsupials, eutherians, and therians of metatherian–eutherian grade provide data indicating that some derived features of the dentary and dentition (e.g., loss of coronoid, meckelian groove, and labial mandibular foramen; acquisition of strong, “winged” conules, double rank postvallum/prevallid shearing, and stylar cusp D) probably arose independently, in some cases more than once, among the major groups of tribosphenic mammals. In turn, this suggests that a common ancestor for marsupials and placentals was more primitive than has generally been appreciated.     

Morphological features of Jat dentition

Observations on morphological characters of milk and permanent teeth, based on 648 pairs of dental casts of 356 male and 292 female Jat children of Haryana (India) are reported. Deciduous teeth show high frequencies of bilateral winging of maxillary central incisor, Carabelli's cusp of maxillary second molar, and deflecting wrinkle of mandibular second molar. Reduction of maxillary molar cusps is more marked in males than in females. Y pattern is very common in deciduous molars. Permanent teeth have high frequencies of grooved cingulum of incisors, cingular nodule of lateral incisors and canines, and distal accessary ridge of canines. Low frequencies of Carabelli's cusp and winging are also common. The tendency towards faintly developed shovelling in milk incisors occurs more often than in the permanent teeth.     

山西垣曲先炭兽类一新种

本文主要报道1983年9月,在山西省垣曲县寨里发现的一件较完整的先炭兽类老年个体上颌骨.带有颇为完整的左、右齿列. I~1-P~2 各齿前、后均有较长的齿隙. P~1、P~2、P~3 前的齿隙颌骨上,保留有乳前臼齿的齿槽.这块标本在大小及形态特征上,与目前所知先炭兽属 Anthracokeryx 中任何种都有相当大的差异.它代表了该属中的一个新种.     

The allometry of relative cusp size in hominoid mandibular molars

The crown area (MCBA) and cusp areas of mandibular molars of Homo sapiens (M-1 = 131; M-2 = 71), Gorilla (M-1 = 25) and Pongo (M-1 = 24) were studied to determine whether the relative size of the mesial and distal cusps are related to overall crown size. Allometric trends were assessed by examining the correlation between relative cusp areas and MCBA and by calculating the slope of the regression line of log cusp area and log MCBA. With the exception of the metaconid in the Homo sapiens M-2S, the results of the intraspecific analyses provide little evidence of an allometric trend for relative reduction of the mesial cusps with increasing crown size. None of the samples provide consistent or reliable evidence of such a trend for the protoconid, nor do the M-1 samples provide evidence for such a trend for the metaconid. The evidence from the distal cusps is also mixed: positive allometry for the entoconid for the Homo sapiens M-2S and for the hypoconulid for the Homo sapiens M-1S, with no departure from isometry in either Gorilla or Pongo. The interspecific data provide no evidence of any trend for the mesial cusps to decrease or the distal cusps to increase in importance in larger teeth. If one accepts the proposition that the static allometric trends observed in this study are reasonable analogues for any allometric relationships within, or between, fossil hominid taxa, then the evidence presented above does not support the hypothesis that the reduction of the trigonid, which is observed in the "robust" australopithecines, is an allometric phenomenon.     

Enamel thickness of deciduous and permanent molars in modern Homo sapiens

This study presents data on the enamel thickness of deciduous (dm2) and permanent (M1-M3) molars for a geographically diverse sample of modern humans. Measurements were recorded from sections through the mesial cusps of unworn teeth. Enamel is significantly thinner on deciduous than on permanent molars, and there is a distinct trend for enamel to increase in relative thickness from M1 to M3. The relatively thicker enamel of M2s and especially M3s can be related to the overall reduction in size of more distal molar crowns, which has been attained through a differential loss of the dentine component. Enamel tends to be thicker on the protocone than on the paracone, and thicker on the protoconid than on the metaconid, but its distribution is not wholly concordant with models that predict increased thickness as a means by which to counter heavier attritional loss on these "functional" cusps. Indeed, the thickness of enamel tends to be more variable on cusp tips and occlusal surfaces than over the lateral aspects of cusps. The proportionately thicker enamel over the lateral aspects of the protocone and protoconid more likely serves as a means to prolong functional crown life by preventing cusp fracture, rather than being an adaptation to increase the attritional longevity of wear facets. The present data suggest that the human dentition is not predisposed to develop a helicoidal wear plane through the disposition of molar enamel thickness.     

Modularity in the mammalian dentition: mice and monkeys share a common dental genetic architecture

The concept of modularity provides a useful tool for exploring the relationship between genotype and phenotype. Here, we use quantitative genetics to identify modularity within the mammalian dentition, connecting the genetics of organogenesis to the genetics of population-level variation for a phenotype well represented in the fossil record. We estimated the correlations between dental traits owing to the shared additive effects of genes (pleiotropy) and compared the pleiotropic relationships among homologous traits in two evolutionary distant taxa-mice and baboons. We find that in both mice and baboons, who shared a common ancestor >65 Ma, incisor size variation is genetically independent of molar size variation. Furthermore, baboon premolars show independent genetic variation from incisors, suggesting that a modular genetic architecture separates incisors from these posterior teeth as well. Such genetic independence between modules provides an explanation for the extensive diversity of incisor size variation seen throughout mammalian evolution-variation uncorrelated with equivalent levels of postcanine tooth size variation. The modularity identified here is supported by the odontogenic homeobox code proposed for the patterning of the rodent dentition. The baboon postcanine pattern of incomplete pleiotropy is also consistent with predictions from the morphogenetic field model.     

Carnivorous dental adaptations in tribosphenic mammals and phylogenetic reconstruction

The molar morphology and structure of seven groups of flesh-eating mammals (Deltatheroida, Borhyaenoidea, Stagodontidae, Dasyuroidea, Creodonta, Carnivora, and Prionogale ) are compared. The dental adaptations to carnivorous diet are remarkably similar in the seven groups. Derived taxa within these groups all possess a postvallum-prevallid shearing with a reduction of the paracone relative to the metacone (except in the Deltatheroida), a large postmetacrista, a reduced stylar shelf, a reduced protocone, a large blade-like paraconid and a reduced metaconid and talonid. The constancy of these features (regarded as a single functional complex) and of their evolutionary pattern in phylogenetically distant groups, is evidence of their high potential for homoplasy. Therefore these character states should be used with extreme care in reconstructing phylogeny and, when possible, associated to cranial features. Several phylogenetic interpretations using them are discussed, some of which are regarded as poorly supported.     

A new protictithere from the late Miocene hominoid locality Ravin de la Pluie of Axios Valley (Macedonia, Greece)

This article concerns the study of a protictithere from the late Miocene of Axios Valley (Macedonia, Greece). The material was found in the hominoid-bearing mammal locality Ravin de la Pluie (RPl), which is corellated with the late Vallesian, MN 10. The available material, including maxillary and mandibular elements, is described and compared morphologically and metrically with the known Eurasian protictitheres. The small size, the low cusps(-ids) of the teeth, the protocone of the P4, which is in line with the mesial border of the parastyle, the large molars (especially the M2), the small buccal projection of the M1 paracone, the strongly molarized p4, the strong metaconid and large talonid with high entoconid of the m1 separate the RPl protictithere from the known Eurasian protictitheres and allow the erection of a new species, named P. thessalonikensis n. sp.     

Geometric morphometric 3D shape analysis and covariation of human mandibular and maxillary first molars

Dental casts of 160 Greek subjects (80 males, 80 females) were scanned by a structured‐light scanner. The upper and lower right first molar occlusal surface 3D meshes were processed using geometric morphometric methods. A total of 265 and 274 curve and surface sliding semilandmarks were placed on the upper and lower molar surfaces, respectively. Principal component analysis and partial least square analysis were performed to assess shape parameters. Molars tended to vary between an elongated and a more square form. The first two principal components (PCs), comprising almost 1/3 of molar shape variation, were related to mesiodistal–buccolingual ratios and relative cusp position. Distal cusps displayed the greatest shape variability. Molars of males were larger than those of females (2.8 and 3.2% for upper and lower molars respectively), but no shape dimorphism was observed. Upper and lower molar sizes were significantly correlated (r² = 0.689). Allometry was observed for both teeth. Larger lower molars were associated with shorter cusps, expansion of the distal cusp, and constriction of the mesial cusps (predicted variance 3.25%). Upper molars displayed weaker allometry (predicted variance 1.59%). Upper and lower molar shape covariation proved significant (RV = 17.26%, P < 0.0001). The main parameter of molar covariation in partial least square axis 1, contributing to 30% of total covariation, was cusp height, in contrast to the primary variability traits exhibited by PC1 and PC2. The aim of this study was to evaluate shape variation and covariation, including allometry and sexual dimorphism, of maxillary and mandibular first permanent molar occlusal surfaces. Am J Phys Anthropol 152:186–196, 2013. © 2013 Wiley Periodicals, Inc.     

Evolution of the Tribosphenic Molar Pattern in Early Mammals,with Comments on the “Dual-Origin” Hypothesis

Development of the tribosphenic molar was a fundamental event that likely influenced the rise of modern mammals. This multi-functional complex combined shearing and grinding in a single chewing stroke, and provided the base morphology for the later evolution of the myriad dental morphologies employed by mammals today. Here a series of morphotypes are presented that represent stepwise acquisition of characters of the molar crown, in an effort to clarify homologies and functional analogies among molars of tribosphenic and tribosphenic-like mammals, as well as their putative sister groups. This is accomplished by evaluation of wear features, which provide direct evidence of occlusal function, and mapping these features on molars of the various morphotypes demonstrates their utility in determining homology. The original singular lower molar talonid cusp is homologous with the hypoconid, and upper molar cusp C in early mammals is homologous with the metacone (cusp “C” is a neomorph with variable occurrence). The lingual translation of the metacone to a position more directly distal to the paracone (as in Peramus) creates an embrasure for the lower molar hypoconid, and is accompanied by the development of the hypoconulid and a new shearing surface. Lastly, the Gondwanan radiation of tribosphenic-like mammals, the Australosphenida (including monotremes), is determined to be functionally non-tribosphenic. The Tribosphenida are restricted to Laurasian taxa, with an origin at or just prior to the Jurassic-Cretaceous boundary.     

A morphometric analysis of maxillary molar crowns of Middle-Late Pleistocene hominins

This study explores the significance of shape differences in the maxillary first molar crowns of Neandertals and anatomically modern humans. It uses morphometric analysis to quantify these differences and to investigate how the orientation of major cusps, relative cusp base areas and occlusal polygon area influence crown shape. The aims of this study were to 1) quantify these data to test whether the tooth shapes of Neandertals and anatomically modern humans differ significantly and 2) to explore if either of the shapes is derived relative to earlier fossil hominins. Data were collected from digital occlusal photographs using image-processing software. Cusp angles, relative cusp base areas and occlusal polygon areas were measured on Neandertals (n=15), contemporary modern humans (n=62), Upper Paleolithic humans (n=6), early anatomically modern humans (n=3) and Homo erectus (n=3). Univariate and multivariate statistical tests were used to evaluate the differences between contemporary modern humans and Neandertals, while the much sparser data sets from the other fossil samples were included primarily for comparison. Statistically significant differences reflecting overall crown shape and internal placement of the crown apices were found. Neandertals are distinguished from contemporary humans by possessing maxillary first molars that 1) are markedly skewed; 2) possess a narrower distal segment of the occlusal polygon compared to the mesial segment; 3) possess a significantly smaller metacone and a significantly larger hypocone; and 4) possess a significantly smaller relative occlusal polygon area reflecting internally placed cusps. Differences in relative cusp base areas of the hypocone and metacone may contribute to the shape differences observed in Neandertals. However, early anatomically modern humans possessing a pattern of relative cusp base areas similar to Neandertals lack their unusual shape. That the morphology observed in non-Neandertal fossil hominins is more anatomically modern human-like than Neandertal-like, suggests that this distinctive morphology may be derived in Neandertals.