共查询到20条相似文献，搜索用时 15 毫秒
1.
哺乳动物化石牙齿釉质能有效地抵抗成岩作用的影响,并保存原始的碳、氧稳定同位素组成信息。通过对食草类哺乳动物化石牙齿釉质同位素组成的分析可以重建这些动物生存时代的古气候。釉质碳酸盐的碳同位素组成响应于取食植物的碳同位素组成,藉此可以恢复陆地生态系统中C3和C4植物的分布比例,这个比例主要受控于大气的CO2水平、气压和光照等因素,与不同的纬度带和气候带有关;釉质磷酸盐的氧同位素组成响应于饮用水的氧同位素组成,饮用水来源于大气降水,其氧同位素组成响应于温度变化,所以釉质的氧同位素组成与气温之间有显著的线性相关,藉此可以计算地史时期的年平均温度、绘制气候的冷暖变化曲线。 相似文献
2.
Teeth are central for the study of ecology, as teeth are at the direct interface between an organism and its environment. Recent years have witnessed a rapid growth in the use of teeth to understand a broad range of topics in living and fossil primate biology. This in part reflects new techniques for assessing ways in which teeth respond to, and interact with, an organism's environment. Long-term studies of wild primate populations that integrate dental analyses have also provided a new context for understanding primate interactions with their environments. These new techniques and long-term field studies have allowed the development of a new perspective-dental ecology. We define dental ecology as the broad study of how teeth respond to, or interact with, the environment. This includes identifying patterns of dental pathology and tooth use-wear, as they reflect feeding ecology, behavior, and habitat variation, including areas impacted by anthropogenic disturbance, and how dental development can reflect environmental change and/or stress. The dental ecology approach, built on collaboration between dental experts and ecologists, holds the potential to provide an important theoretical and practical framework for inferring ecology and behavior of fossil forms, for assessing environmental change in living populations, and for understanding ways in which habitat impacts primate growth and development. This symposium issue brings together experts on dental morphology, growth and development, tooth wear and health, primate ecology, and paleontology, to explore the broad application of dental ecology to questions of how living and fossil primates interact with their environments. 相似文献
3.
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
4.
Guatelli-Steinberg D 《American journal of physical anthropology》2003,120(4):309-322
This study uses macroscopic and microscopic methods to analyze the expression of linear enamel hypoplasia (LEH) in Plio-Pleistocene South African hominins. LEH is a developmental defect of enamel that is used in many anthropological contexts as a physiological stress indicator. Previous research has not settled the question as to whether differences in LEH expression exist between Paranthropus and Australopithecus and if they exist, to what extent these differences might be explained simply by taxonomic differences in enamel development and morphology rather than by differential stress experience. In this study, the analysis of LEH is conducted with respect to differences between Paranthropus and Australopithecus in aspects of enamel development and morphology that are thought to influence LEH expression. Two factors impacting LEH expression are considered: the duration of enamel formation, and the spacing of perikymata. It is predicted that if the first factor strongly influences the expression of LEH, then there should be fewer defects per tooth in Paranthropus because of its abbreviated crown formation spans (and fast extension rates) relative to Australopithecus. It is also predicted that because Australopithecus has more densely packed perikymata in comparable regions of the crown than Paranthropus, this taxon should, on average, have narrower defects than Paranthropus. To address these questions, 200 Australopithecus and 137 Paranthropus teeth were examined for LEH, and the analysis of defect width with respect to perikymata spacing was conducted on tooth impressions examined under a scanning electron microscope using INCA (Oxford Instruments) measurement software. Data support the first prediction: Australopithecus does have significantly more defects per canine tooth than Paranthropus. Data do not support the second prediction in large part because several Australopithecus specimens have wide groove defects in which perikymata are not visible and enamel is irregular. Such wide grooves are not predicted by perikymata spacing such that alternative explanations, including taxonomic differences in ameloblast sensitivity and the duration/severity of disruptions to enamel growth, must be considered. 相似文献
5.
Guatelli-Steinberg D Ferrell RJ Spence J 《American journal of physical anthropology》2012,148(2):191-204
Physiological stress, such as malnutrition or illness, can disrupt normal enamel growth, resulting in linear enamel hypoplasias (LEHs). Although ecological factors may contribute to LEH expression, other factors, such as surface abrasion and enamel growth variables, are also likely to be involved. Attention to these other factors is necessary before we can begin to understand what LEH might signify in terms of ecological sources of physiological stress in non-human primates. This study focuses on assessing the contribution of these other factors to variation in LEH expression within and across great ape taxa. Here, we present LEH data from unabraded crown regions in samples of seven great ape species. We analyze these data with respect to lateral enamel formation time and the angles that striae of Retzius make with the enamel surface, as these variables are expected to affect variation in LEH expression. We find that although the duration of enamel formation is associated with sex differences in LEH expression, it is not clearly related to taxonomic variation in LEH expression, and does not explain the low frequency of LEH in mountain gorillas found in this and a previous study. Our data on striae of Retzius angles suggest that these influence LEH expression along the tooth crown and may contribute to the consistently high frequencies of LEH seen in Pongo in this and previous studies. We suggest that future work aimed at understanding species variation in these angles is crucial to evaluating taxonomic patterns of LEH expression in great apes. 相似文献
6.
Sunny H. Hwang 《Biological reviews of the Cambridge Philosophical Society》2011,86(1):183-216
The evolution of tooth enamel microstructure in both extinct and extant mammalian groups has been extensively documented, but is poorly known in reptiles, including dinosaurs. Previous intensive sampling of dinosaur tooth enamel microstructure revealed that: (1) the three‐dimensional arrangement of enamel types and features within a tooth—the schmelzmuster—is most useful in diagnosing dinosaur clades at or around the family level; (2) enamel microstructure complexity is correlated with tooth morphology complexity and not necessarily with phylogenetic position; and (3) there is a large amount of homoplasy within Theropoda but much less within Ornithischia. In this study, the examination of the enamel microstructure of 28 additional dinosaur taxa fills in taxonomic gaps of previous studies and reinforces the aforementioned conclusions. Additionally, these new specimens reveal that within clades such as Sauropodomorpha, Neotheropoda, and Euornithopoda, the more basal taxa have simpler enamel that is a precursor to the more complex enamel of more derived taxa and that schmelzmusters evolve in a stepwise fashion. In the particularly well‐sampled clade of Euornithopoda, correlations between the evolution of dental and enamel characters could be drawn. The ancestral schmelzmuster for Genasauria remains ambiguous due to the dearth of basal ornithischian teeth available for study. These new specimens provide new insights into the evolution of tooth enamel microstructure in dinosaurs, emphasizing the importance of thorough sampling within broadly inclusive clades, especially among their more basal members. 相似文献
7.
8.
9.
Mark F. Teaford 《Evolutionary anthropology》1994,3(1):17-30
Investigators have used many techniques to understand diet and tooth use in prehistoric species. A promising new addition to the analytical arsenal is dental microwear analysis—the study of microscopic wear patterns on teeth. On-going work is proceeding on a number of fronts. Studies of modern animals are showing some of the limits of resolution of the technique, while studies of prehistoric animals are answering many new questions and raising still more in the process. Much work remains to be done, but one thing is clear: if we proceed cautiously, we can provide new insights into the evolution of diet and tooth use. 相似文献
10.
David V. Lee Tudor N. Comanescu Michael T. Butcher John E. A. Bertram 《Proceedings. Biological sciences / The Royal Society》2013,280(1771)
This study compares human walking and running, and places them within the context of other mammalian gaits. We use a collision-based approach to analyse the fundamental dynamics of the centre of mass (CoM) according to three angles derived from the instantaneous force and velocity vectors. These dimensionless angles permit comparisons across gait, species and size. The collision angle Φ, which is equivalent to the dimensionless mechanical cost of transport CoTmech, is found to be three times greater during running than walking of humans. This threefold difference is consistent with previous studies of walking versus trotting of quadrupeds, albeit tends to be greater in the gaits of humans and hopping bipeds than in quadrupeds. Plotting the collision angle Φ together with the angles of the CoM force vector Θ and velocity vector Λ results in the functional grouping of bipedal and quadrupedal gaits according to their CoM dynamics—walking, galloping and ambling are distinguished as separate gaits that employ collision reduction, whereas trotting, running and hopping employ little collision reduction and represent more of a continuum that is influenced by dimensionless speed. Comparable with quadrupedal mammals, collision fraction (the ratio of actual to potential collision) is 0.51 during walking and 0.89 during running, indicating substantial collision reduction during walking, but not running, of humans. 相似文献
11.
Guatelli-Steinberg D 《American journal of physical anthropology》2004,123(3):199-215
This study of linear enamel hypoplasia (LEH) in Plio-Pleistocene hominins builds on a previous study (Guatelli-Steinberg [2003] Am. J. Phys. Anthropol. 120:309-322) that focused on LEH in early South African hominins. The present study is more comprehensive, encompassing dental specimens of hominins from East Africa as well, including early Homo. As a developmental defect of enamel, LEH is used in anthropological contexts to reveal information about physiological stress. However, intrinsic aspects of enamel development and morphology can affect the expression of LEH, complicating efforts to understand the significance of these defects. In this study, the analysis of LEH is conducted with respect to enamel development and morphology. It is predicted that Paranthropus should have fewer defects on its canine teeth than Australopithecus and Homo, owing to its abbreviated period of enamel formation. This prediction is supported: Paranthropus has statistically significantly fewer defects per canine than Australopithecus and Homo. The previous study demonstrated that despite the wider spacing of perikymata on the teeth of South African Paranthropus, defects on the canine teeth of this genus were not wider than those of Australopithecus. A multiple linear regression analysis in that study, as well as a separate analysis in the present study, indicate that the number of perikymata within defects is a better predictor of defect width than perikymata spacing. In this study, it was additionally found that the average number of perikymata within Australopithecus defects is statistically significantly greater than it is in Paranthropus, thus explaining why Paranthropus defects are not wider than those of Australopithecus. The biological significance of this difference in the number of perikymata within the defects of Australopithecus and Paranthropus is considered in light of several factors, including: 1) the possibility that other intrinsic attributes of enamel morphology may be involved (specifically the faster extension rates of Paranthropus that result in shallower defects), 2) generic differences in the canalization of enamel development, and 3) generic differences in the duration of disruptions to enamel growth. 相似文献
12.
This study investigates changes in the prevalence of linear enamel hypoplasia (LEH) before and after the shift from irregular to regular provisioning in the Cayo Santiago rhesus monkey population. Prior to 1956, monkeys on this island colony did not receive consistent provisions, and were reported to be in poor health (Rawlins and Kessler [1986] The Cayo Santiago Macaques; Albany: State University of New York Press). A regular provisioning program, instituted in August 1956, resulted in the improved health of individuals and the growth of the population (Rawlins and Kessler [1986] The Cayo Santiago Macaques; Albany: State University of New York Press). LEH, a developmental defect of enamel, is a sensitive indicator of systemic physiological stress (Goodman and Rose [1990] Yrbk. Phys. Anthropol. 33:59-110). It was therefore hypothesized that the prevalence of LEH would be higher in monkeys who were irregularly provisioned than in monkeys who experienced regular provisioning. To test this hypothesis, teeth were examined for LEH in a sample of 181 female rhesus monkeys. The results support the hypothesis: the mean number of defects was statistically significantly higher in the preprovisioned group than it was in the postprovisioned one. When LEH prevalence was assessed using only defects occurring on antimeric pairs, the preprovisioned group again had a higher prevalence than the postprovisioned one, although the difference was not statistically significant, most likely because of the reduced sample size. The results of this study indicate that changes in LEH prevalence, at least in this population of rhesus monkeys, are associated with changes in nutritional status. 相似文献
13.
14.
Zhixing Yi Wei Liao Clément Zanolli Wei Wang 《American journal of physical anthropology》2021,174(3):555-567
15.
16.
Moya Meredith Smith 《Historical Biology》2013,25(1-2):97-126
The property of tooth enamel to resist alteration during fossilization, is used to analyse the unique arrangements of biological crystallites amongst genera of Paleozoic sarcopterygians, with both polarized light and s.e.m. Previous concepts of crystallite organization in reptiles and mammal‐like reptiles are evaluated. Two of the Devonian sarcopterygians, are shown to exhibit a protoprismatic pattern, identical with that of a stem group therian. The patterns of crystallites, together with the arrangement of incremental lines establish that this tissue is solely an ectodermal product; monotypic enamel, in contrast to bitypic enamel with two cell products contributing to it as in enameloid or acrodin. Each genus examined has a different pattern, of significance in considering relationships amongst sarcopterygians. Recent information on ganoine and some new findings on enamel in extant lungfishes have led to the conclusion that types of monotypic enamel are present in both actinopterygians and sarcopterygians, and challenges the use of monotypic enamel as a synapomorphy of sarcopterygians in cladistic analyses. 相似文献
17.
Pseudogenization of the tooth gene enamelysin (MMP20) in the common ancestor of extant baleen whales
Robert W. Meredith John Gatesy Joyce Cheng Mark S. Springer 《Proceedings. Biological sciences / The Royal Society》2011,278(1708):993-1002
Whales in the suborder Mysticeti are filter feeders that use baleen to sift zooplankton and small fish from ocean waters. Adult mysticetes lack teeth, although tooth buds are present in foetal stages. Cladistic analyses suggest that functional teeth were lost in the common ancestor of crown-group Mysticeti. DNA sequences for the tooth-specific genes, ameloblastin (AMBN), enamelin (ENAM) and amelogenin (AMEL), have frameshift mutations and/or stop codons in this taxon, but none of these molecular cavities are shared by all extant mysticetes. Here, we provide the first evidence for pseudogenization of a tooth gene, enamelysin (MMP20), in the common ancestor of living baleen whales. Specifically, pseudogenization resulted from the insertion of a CHR-2 SINE retroposon in exon 2 of MMP20. Genomic and palaeontological data now provide congruent support for the loss of enamel-capped teeth on the common ancestral branch of crown-group mysticetes. The new data for MMP20 also document a polymorphic stop codon in exon 2 of the pygmy sperm whale (Kogia breviceps), which has enamel-less teeth. These results, in conjunction with the evidence for pseudogenization of MMP20 in Hoffmann''s two-toed sloth (Choloepus hoffmanni), another enamel-less species, support the hypothesis that the only unique, non-overlapping function of the MMP20 gene is in enamel formation. 相似文献
18.
Jason B. Ramsay Cheryl D. Wilga Leif Tapanila Jesse Pruitt Alan Pradel Robert Schlader Dominique A. Didier 《Journal of morphology》2015,276(1):47-64
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. 相似文献
19.
Donald J. Reid Debbie Guatelli‐Steinberg 《American journal of physical anthropology》2017,162(4):817-829