共查询到20条相似文献，搜索用时 15 毫秒
1.
Grine FE Spencer MA Demes B Smith HF Strait DS Constant DA 《American journal of physical anthropology》2005,128(4):812-822
Modern humans exhibit increasing relative enamel thickness from M1 to M3. Some biomechanical (basic lever) models predict that the more distal molars in humans encounter higher occlusal forces, and it has been postulated that this provides a functional explanation for the observed gradient in relative enamel thickness. However, constrained three-dimensional models and experimental observations suggest that there is a reduction in bite force potential from M1 to M3, which would be consistent with the tendency for humans to reduce the size of the distal molars. In this regard, it has been postulated that the distal increase in enamel thickness is a consequence of crown size reduction; thus, it is unnecessary to invoke functional scenarios to explain this phenomenon. We assess these competing proposals by examining relative enamel thickness in a catarrhine primate (Papio ursinus) that exhibits crown size increase from M1 to M3. The molar row of P. ursinus is positioned relatively far forward of the temporomandibular joint, which results in the baboon being able to exert relatively greater muscle forces during posterior biting in comparison to modern humans. Thus, a significant distalward gradient of increasing enamel thickness would be expected in P. ursinus according to the hypothesis that posits it to be functionally related to bite force. The present study reveals no significant difference in relative enamel thickness along the molar row in P. ursinus. This finding lends support to the notion that the relatively thicker enamel of human distal molars is related primarily to their reduction in size. This carries potential implications for the interpretation of enamel thickness in phylogenetic reconstructions: the relatively thick molar enamel shared by modern humans and some of our fossil relatives may not be strictly homologous, in that it may result from different underlying developmental mechanisms. 相似文献
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Granulin epithelin precursor (GEP) is a new growth factor that functions in brain development, chondrogenesis, tissue regeneration, tumorigenesis, and inflammation. The goal of this study was to study whether GEP was critical for odontogenesis and amelogenesis both in vivo and in vitro. The in situ hybridization and immunohistochemistry data showed that GEP was expressed in both odontoblast and ameloblast cells postnatally. Knockdown of GEP by crossing U6-ploxPneo-GEP and Sox2-Cre transgenic mice led to a reduction of dentin thickness, an increase in predentin thickness, and a reduction in mineral content in enamel. The in vitro application of recombinant GEP up-regulated molecular markers important for odontogenesis (DMP1, DSPP, and ALP) and amelogenesis (ameloblastin, amelogenin and enamelin). In conclusion, both the in vivo and the in vivo data support an important role of GEP in tooth formation during postnatal development. 相似文献
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Smith TM Olejniczak AJ Reh S Reid DJ Hublin JJ 《American journal of physical anthropology》2008,136(2):237-241
In addition to evidence for bipedality in some fossil taxa, molar enamel thickness is among the few characters distinguishing (thick-enameled) hominins from the (thin-enameled) African apes. Despite the importance of enamel thickness in taxonomic discussions and a long history of scholarship, measurements of enamel thickness are performed almost exclusively on molars, with relatively few studies examining premolars and anterior teeth. This focus on molars has limited the scope of enamel thickness studies (i.e., there exist many fossil hominin incisors, canines, and premolars). Increasing the available sample of teeth from which to compare enamel thickness measurements from the fossil record could substantially increase our understanding of this aspect of dental biology, and perhaps facilitate greater taxonomic resolution of early hominin fossils. In this study, we report absolute and relative (size-scaled) enamel thickness measurements for the complete dentition of modern humans and chimpanzees. In accord with previous studies of molars, chimpanzees show lower relative enamel thickness at each tooth position, with little overlap between the two taxa. A significant trend of increasing enamel thickness from anterior to posterior teeth is apparent in both humans and chimpanzees, indicating that inter-taxon comparisons should be limited to the same tooth position in order to compare homologous structures. As nondestructive imaging techniques become commonplace (facilitating the examination of increasing numbers of fossil specimens), studies may maximize available samples by expanding beyond molars. 相似文献
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Smith TM Kupczik K Machanda Z Skinner MM Zermeno JP 《American journal of physical anthropology》2012,147(3):417-426
Dental enamel thickness has received considerable attention in ecological models of the adaptive significance of primate morphology. Several authors have theorized that the degree of enamel thickness may reflect selective pressures related to the consumption of fallback foods (dietary items that may require complex processing and/or have low nutritional value) during times of preferred food scarcity. Others have speculated that enamel thickness reflects selection during mastication of foods with particular material properties (i.e., toughness and hardness). Orangutans prefer ripe fruit when available, but show interspecific and sex differences in the consumption of fallback foods (bark, leaves, and figs) and other preferred foods (certain seeds). Bornean orangutans (Pongo pygmaeus) have also been reported to masticate more mechanically demanding foods than Sumatran orangutans (Pongo abelii). To test these ecological models, we assessed two-dimensional enamel thickness in orangutan full dentitions using established histological and virtual quantification methods. No significant differences in average enamel thickness (AET) were found between species. We found significant differences in the components of enamel thickness indices between sexes, with males showing greater enamel-dentine junction lengths and dentine core areas, and thus relatively thinner enamel than females. Comparisons of individuals of known sex and species revealed a dentition-wide trend for Bornean females to show greater AET than Sumatran females. Differences between small samples of males were less evident. These data provide only limited support for ecological explanations of enamel thickness patterns within great ape genera. Future studies of dietary ecology and enamel thickness should consider sex differences more systematically. 相似文献
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Casey J. Self 《Journal of morphology》2015,276(9):1065-1074
The relationship between tooth roots and diet is relatively unexplored, although a logical relationship between harder diets and increased root surface area (RSA) is suggested. This study addresses the interaction between tooth morphology, diet, and bite force in small mammals, phyllostomid bats. Using micro computed tomography (microCT), tooth root morphology of two fruit‐eating species (Carollia perspicillata and Chiroderma villosum) and two insect‐eating species (Mimon bennettii and Macrotus californicus) was compared. These species did not differ in skull or estimated body size. Food hardness, rather than dietary classification, proved to be the strongest grouping factor, with the two insectivores and the seed‐processing frugivore (C. villosum) having significantly larger RSAs. Bite force was estimated using skull measurements; bite force significantly correlated with tooth RSA but not with body size. Although the three durophagous species did exhibit larger crowns, the area of the occlusal surface did not vary among the four species. There was a linear relationship between root size and crown size, indicating that the roots were not expanded disproportionately; instead the entire tooth was larger in the hard diet species. MicroCT allows the nondestructive quantification of previously difficult‐to‐access tooth morphology; this method shows the potential for tooth roots to provide valuable dietary, behavioral, and ecological information in small mammals. J. Morphol. 276:1065–1074, 2015. © 2015 Wiley Periodicals, Inc. 相似文献
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This study examined the minimum force required of functional teeth and replacement teeth in the tiger shark Galeocerdo cuvier and the sandbar shark Carcharhinus plumbeus to penetrate the scales and muscle of sheepshead Archosargus probatocephalus and pigfish Orthopristis chrysoptera. Penetration force ranged from 7·7–41·9 and 3·2–26·3 N to penetrate A. probatocephalus and O. chrysoptera, respectively. Replacement teeth required significantly less force to penetrate O. chrysoptera for both shark species, most probably due to microscopic wear of the tooth surfaces supporting the theory shark teeth are replaced regularly to ensure sharp teeth that are efficient for prey capture. 相似文献
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PER CHRISTIANSEN 《Zoological Journal of the Linnean Society》2007,151(2):423-437
The sabretooth felids were widespread across much of the world in the Late Tertiary, and appear to have been an important group of large predators. Owing to the substantially different skull morphology of derived sabretooths compared with extant felids, there has been considerable debate over the killing mode, bite forces, and bending strength of the large upper canines, and over the implications of these characteristics on feeding ecology. Debates have, however, usually been based on indirect comparisons of force vectors. In this paper, I provide assessments of the estimated force output from the jaw adductor muscles, based on estimates of muscle cross-sectional areas and force vectors, along with canine bending strengths, in a variety of sabretooth felids, in comparison with extant felids. In general, sabretoothed felids had moderately powerful bites, albeit with less jaw adductor power for their body sizes compared with extant felids, sometimes markedly so. Less derived sabrecats appear to have had proportionally higher bite forces than derived forms. The length of the upper canines seemingly compromised their bending strength at any given body size, and again this was most marked in derived forms. However, compared with estimated jaw adductor forces, the canines of sabrecats appear, if anything, to have been stronger than those of extant conical-toothed felids. It has previously been suggested that large sabretoothed felids hunted large prey with a canine shearing bite, powered in part by the jaw adductors and in part by the muscles of the upper neck–occipital region. The present results of canine bending strengths versus the predicted bite force from the jaw adductors supports this suggestion. © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society , 2007, 151 , 423–437. 相似文献
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Zhixing Yi Wei Liao Clément Zanolli Wei Wang 《American journal of physical anthropology》2021,174(3):555-567
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Callitrichines share several morphological features that appear to be derived among anthropoid primates. One view maintains that some of them are the consequence of a rapid reduction in body size in the common ancestor of callitrichines. This hypothesis predicts that callitrichines should have relatively large teeth for their body size in comparison to other platyrrhines. Dental metric data from 18 platyrrhine species, including 4 callitrichines, is used to test this hypothesis. Callitrichine tooth size is compared both to empirical regressions of tooth size against body weight for noncallitrichine platyrrhines and to a prediction of geometric similarity. In neither comparison do callitrichines as a group show significantly greater tooth size than other platyrrhines. In fact, three of the four genera seem to have relatively small teeth for their body size. While this study fails to support the hypothesis that the common ancestor of callitrichines underwent a rapid reduction in body size, it neither proves nor disproves the hypothesis that they are smaller than their last common ancestor. 相似文献
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On average, males possess larger tooth crowns than females in contemporary human populations, although the degree of dimorphism varies within different populations. In previous studies, different amounts of either enamel or dentine were implicated as the cause of this dimorphism. In this study, we attempt to determine the nature of sexual dimorphism in the crowns of permanent modern human teeth and to determine if two contrasting tooth types (permanent third molars and canines) show identical patterns of dimorphism in enamel and dentine distribution. We estimated the relative contributions of both enamel and dentine to total crown size, from buccolingual sections of teeth. Our sample consisted of a total of 144 mandibular permanent third molars and 25 permanent mandibular canines of known sex. We show that sexual dimorphism is likely due, in part, to the presence of relatively more dentine in the crowns of male teeth. However, whatever the underlying cause, dimorphism in both tooth root and tooth crown size should produce measurable dimorphism in tooth weight, though this has not been previously explored. Therefore, we provide some preliminary data that indicate the usefulness of wet tooth weight as a measure of sexual dimorphism. Both male permanent third molars and canines are significantly heavier than those of females. The weight dimorphism reported here for both classes of teeth may prove a useful finding for future forensic studies. In particular, weights of canines may be more useful as a means of sexing modern human skeletal material than linear or area measurements of teeth. 相似文献
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Glenn C. Conroy 《International journal of primatology》1987,8(2):115-137
Body-weight estimates of fossil primates are commonly used to infer many important aspects of primate paleobiology, including
diet, ecology, and relative encephalization. It is important to examine carefully the methodologies and problems associated
with such estimates and the degree to which one can have confidence in them. New regression equations for predicting body
weight in fossil primates are given which provide body-weight estimates for most nonhominid primate species in the fossil
record. The consequences of using different subgroups (evolutionary “grades”) of primate species to estimate fossil-primate
body weights are explored and the implications of these results for interpreting the primate fossil record are discussed.
All species (fossil and extant) were separated into the following “grades”: prosimian grade, monkey grade, ape grade, anthropoid
grade, and all-primates grade. Regression equations relating lower molar size to body weight for each of these grades were
then calculated. In addition, a female-anthropoid grade regression was also calculated for predicting body weight infernales
of extinct, sexually dimorphic anthropoid species. These equations were then used to generate the fossil-primate body weights.
In many instances, the predicted fossil-primate body weights differ substantially from previous estimates. 相似文献
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The pattern of variation and covariation of proximal and distal limb segment lengths was examined within and between 20 geographically diverse skeletal samples of modern humans. Analyses of variance-covariance matrices (VCMs) of logarithmically transformed (ln) variates of humerus, radius, femur, and tibia length were performed to test the following hypotheses: first, within populations, the distal and proximal segments will have equal relative (i.e., size-independent) variability. However, between populations, the tibia is predicted to be more variable than the other segments. Tests of fit of computed VCMs to theoretical matrices by an iterative procedure (Anderson [1973] Ann. Stat. 1:135-141) reject the equal variance hypotheses, rather suggesting that the relative variances of the distal limb segments are greater than are those of the proximal. Males and females differ somewhat in that within females, the distal segments of both limbs have equal variance, while within males, the tibia has greater relative variance than the radius. The second hypothesis, regarding between-group variability, is somewhat supported in that between human populations, one cannot reject that the tibia has greater relative variance than the other limb segments. However, neither can one reject an alternative hypothesis that both distal limb segments (tibia and radius) are more variable than the proximal segments. Differential growth allometry is explored, and likely plays a major role in differences seen both within and between human populations. 相似文献
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Robert S. Corruccini 《International journal of primatology》1987,8(2):99-114
Dental characteristics figure large in primate taxonomy because teeth fossilize commonly and reflect dietary adaptations. The mammalian dentinoenamel junction (DEJ) plays a crucial role throughout odontogenesis in determining the ultimate crown configuration, being the interface between the papilla and the dental cap. The final configuration of the dentin surface reflects the epithelium more closely than does the enamel surface of the crown. Enamel deposition occurs relatively late in calcification, often causing many changes from the pattern residing in the DEJ; the genetic determination of the two surfaces also differs. Comparative study of the DEJ (and its differences from the enamel crown) is a potential adjunct to dentition-based taxonomy and may help to resolve certain cusp homologies and morphogenetic order of appearance. Primate teeth were stripped of enamel after measurement, mapping, and anatomical observations on the original crown. The dentin surfaces thus revealed differ from the enamel surfaces in several respects and shed new light on such dental problem areas as the origin of the hypocone, the affinities of lorisoids and callitrichids, the monophyly of the anthropoid grade, and human affinities. 相似文献
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Adam Hartstone‐Rose Jennifer A. Parkinson Taylor Criste Jonathan M.G. Perry 《American journal of physical anthropology》2015,157(3):513-518
Previously we found that Maximum Ingested Bite Size (Vb)—the largest piece of food that an animal will ingest whole without biting first—scales isometrically with body size in 17 species of strepsirrhines at the Duke Lemur Center (DLC). However, because this earlier study focused on only three food types (two with similar mechanical properties), it did not yield results that were easily applied to describing the broad diets of these taxa. Expressing Vb in terms of food mechanical properties allows us to compare data across food types, including foods of wild lemurs, to better understand dietary adaptations in lemurs. To this end, we quantified Vb in five species of lemurs at the DLC representing large and small frugivores and folivores using ten types of food that vary widely in stiffness and toughness to determine how these properties relate to bite sizes. We found that although most species take smaller bites of stiffer foods, this negative relationship was not statistically significant across the whole sample. However, there is a significant relationship between bite size and toughness. All three of the more frugivorous taxa in our sample take significantly smaller bites of tougher foods. However, the two more folivorous lemurs do not. They take small bites for all foods. This suggests that the species most adapted to the consumption of tough foods do not modulate their ingestive sizes to accommodate larger pieces of weak foods. Am J Phys Anthropol 157:513–518, 2015. © 2015 Wiley Periodicals, Inc. 相似文献
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Jonathan M.G. Perry Adam Hartstone‐Rose 《American journal of physical anthropology》2010,142(4):625-635
Little is known about ingested food size (Vb) in primates, even though this variable has potentially important effects on food intake and processing. This study provides the first data on Vb in strepsirrhine primates using a captive sample of 17 species. These data can be used for generating and testing models of feeding energetics. Strepsirrhines are of interest because they are hypometabolic and chewing rate and daily feeding time do not show a significant scaling relationship with body size. Using melon, carrot, and sweet potato we found that maximum Vb scales isometrically with body mass and mandible length. Low dietary quality in larger strepsirrhines might explain why Vb increases with body size at a greater rate than does resting metabolic rate. Relative to body size, Vb is large in frugivores but small in folivores; furthermore scaling slopes are higher in frugivores than in folivores. A gross estimate of dietary quality explains much of the variation in Vb that is not explained by body size. Gape adaptations might favor habitually large bites for frugivores and small ones for folivores. More data are required for several feeding variables and for wild populations. Am J Phys Anthropol 142:625–635, 2010. © 2010 Wiley‐Liss, Inc. 相似文献
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Abstract. We present the first report on the use of the non‐invasive method of synchrotron X‐ray microtomography to model the dynamics and theoretical bite forces of arthropod mouthparts. The nature of the data allowed us to include precise measurements of muscle areas and the spatial geometry of muscle origins and insertions into a biomechanical model of a morphological microstructure. We investigated the functional morphology of the chelicera in the oribatid mite Archegozetes longisetosus (Acari, Oribatida), a model organism for Chelicerata. The chelicera represents a first‐class lever; the intrinsic muscular system consists of a feather‐shaped depressor with six muscle bundles and a bouquet‐shaped levator with 16 bundles. The relative bite forces, as compared with body mass (force/mass2/3), are 390 N kg?1 and lie within those known for vertebrates (≤260 N kg?1) and decapod chelae (≤915 N kg?1). The dynamics of force transmission and bite forces during the movement of the apotele are calculated. The conserved organization of cheliceral musculature allows broad adaptation of the model to other chelicerate taxa. 相似文献