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61.
步氏巨猿(Gigantopithecus blacki)是更新世时期生活于我国华南地区的一种超大型猿类, 它的体态特征和演化分类倍受关注。牙齿釉质厚度在探讨灵长类食性、环境适应以及系统演化方面具有重要意义。本文利用显微CT技术构建18颗巨猿臼齿虚拟模型, 测量其釉质厚度。将巨猿釉质厚度与现代人、现生类人猿、古人类、中新世古猿及其他现生灵长类进行比较, 从牙齿釉质厚度探讨巨猿的食性适应和系统演化问题。结果发现巨猿的实测釉质厚度是目前所有已知现生和化石灵长类中最厚的, 只有傍人、南非早期人属及奥兰诺古猿三种化石灵长类与之接近; 如果考虑不同物种牙齿与身体大小的关联因素, 相对釉质厚度指数显示巨猿属于"厚"釉质类型, 但非"超厚"类型, 低于奥兰诺古猿、傍人、南非早期人属; 巨猿与某些中新世古猿 (如原康修尔猿尼安萨种、非洲古猿)、南方古猿、东非早期人属、亚洲直立人以及现代人、现生卷尾猴的相对釉质厚度指数相近。巨猿的厚釉质特征与其食性和环境适应密切相关, 使得牙齿具有非常强的抗磨损功能, 能够适应长时间的咀嚼和研磨食物。从釉质厚度的系统演化角度推测, 厚釉质应该是人类祖先的特征性状, 巨猿有可能是早期人类支系演化过程中的一个特化旁支, 同时也不排除巨猿是从某种具有厚釉质的中新世古猿旁支平行演化而来的可能性。 相似文献
62.
在步氏巨猿后部齿的绝大部分类别中检出有釉质发育不全的标本,患釉质发育不全的个体数高达14.3—17.9%。类似的情况可见之于南非的南方古猿类。步氏巨猿的釉质发育不全很大可能是由于营养上的原因。 相似文献
63.
Charles R. Peters 《American journal of physical anthropology》1982,57(3):283-301
No living analogue exists for the hypothetical early hominid hard/tough-seed, coarse-root-eating, and bone-crushing masticatory adaptation. To investigate possible microdamage/microwear to dental enamel caused by such usage, puncture-crushing experiments were carried out on single human teeth, using an Instron compression apparatus on the following six test materials: Makapansgat Limeworks chert (e.g., taphonomy), fresh steer longbone, mongongo nuts, Grewia berries, Carob beans, and wild-onion bulbs. Pairs of extracted unworn third molars were utilized, with one tooth acting as the control. The teeth were mounted, ultrasonically cleaned, and two-stage replicas made with a vinyl polysiloxane elastomer and araldite epoxy resin. After Instron loading and materials failure (1.2–395.0 kg) the test items and the crowns were prepared for comparison with scanning electron microscopy and dispersive x-ray elemental analysis and mapping. The results revealed that although grit adhering to food item surfaces caused microscratches (0.1–1.0 μm wide) similar in appearance to those caused by opal phytoliths in grasses, the dicotyledonous seed coats per se were unable to score enamel. This suggests microscratch morphology alone may not provide a reliable indication of food type. In some cases puncture-crushing of bone and hard legumes produced a localized microfracture pattern (crazing with cracks less than or equal to 0.1–1.0 μm wide) that was readily distinguishable from the simulated taphonomic damage caused by chert fragments, suggesting analysis of enamel microfracture patterns may provide clues as to early hominid dietary adaptations. 相似文献
64.
Robert S. Corruccini Jerome S. Handler Robert J. Mutaw Frederick W. Lange 《American journal of physical anthropology》1982,59(4):443-459
A unique seventeenth–nineteenth century slave cemetery population from Newton plantation, Barbados, allows examination of craniodental characters in relation to ethnohistorical data. Age-at-death estimates suggest life expectancy at birth of 29 years and low infant mortality; historical demography, however, suggests life expectancy of 20 years and very high infant mortality. Tooth decay, bilateral tooth loss, periodontal disease, root hypercementosis, and severe enamel hypoplasia are high in frequency. The teeth yield evidence of such cultural practices as pipe-smoking and incisor mutilation. Several skeletal features reflect periodic near-starvation. Directional and fluctuating dental asymmetry, relative tooth size, and hypoplasia distribution suggest slaves experienced considerable weaning trauma; metabolic stress at this time exceeded that of prenatal and immediate postnatal periods. Odontometrics and dental and cranial nonmetric traits indicate that modern Blacks are intermediate between the ancestral slaves and modern Whites but more similar to the latter, suggesting effects of environmental covariance exceed those of genetic admixture. Nonmetric trait distributions show nonrandom patterns according to area of burial in the cemetery, a possible result of family segregation. 相似文献
65.
D G Gantt 《American journal of physical anthropology》1979,51(3):353-360
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. 相似文献
66.
Garry W. Buchko Barbara J. Tarasevich Jacky Roberts Malcolm L. Snead Wendy J. Shaw 《Biochimica et Biophysica Acta - Proteins and Proteomics》2010,1804(9):1768-1774
Amelogenins are the dominant proteins present in ameloblasts during the early stages of enamel biomineralization, making up > 90% of the matrix protein. Along with the full-length protein there are several splice-variant isoforms of amelogenin present including LRAP (Leucine-Rich Amelogenin Protein), a protein that consists of the first 33 and the last 26 residues of full-length amelogenin. Using solution-state NMR spectroscopy we have assigned the 1H-15N HSQC spectrum of murine LRAP (rp(H)LRAP) in 2% acetic acid at pH 3.0 by making extensive use of previous chemical shift assignments for full-length murine amelogenin (rp(H)M180). This correlation was possible because LRAP, like the full-length protein, is intrinsically disordered under these solution conditions. The major difference between the 1H-15N HSQC spectra of rp(H)M180 and rp(H)LRAP was an additional set of amide resonances for each of the seven non-proline residues between S12* and Y12 near the N-terminus of rp(H)LRAP indicating that the N-terminal region of LRAP exists in two different conformations. Analysis of the proline carbon chemical shifts suggests that the molecular basis for the two states is not a cis-trans isomerization of one or more of the proline residues in the N-terminal region. Starting from 2% acetic acid, where rp(H)LRAP was monomeric in solution, NaCl addition effected residue specific changes in molecular dynamics manifested by the reduction in intensity and disappearance of 1H-15N HSQC cross peaks. As observed for the full-length protein, these perturbations may signal early events governing supramolecular self-assembly of rp(H)LRAP into nanospheres. However, the different patterns of 1H-15N HSQC cross peak perturbation between rp(H)LRAP and rp(H)M180 in high salt suggest that the termini may behave differently in their respective nanospheres, and perhaps, these differences contribute to the cell signaling properties attributable to LRAP but not to the full-length protein. 相似文献
67.
Frederic Michon Mark Tummers Marika Kyyrönen Mikko J. Frilander Irma Thesleff 《Developmental biology》2010,340(2):355-368
Teeth form as appendages of the ectoderm and their morphogenesis is regulated by tissue interactions mediated by networks of conserved signal pathways. Micro-RNA (miRNA) pathway has emerged as important regulator of various aspects of embryonic development, but its function in odontogenesis has not been elucidated. We show that the expression of RNAi pathway effectors is dynamic during tooth morphogenesis and differentiation of dental cells. Based on microarray profiling we selected 8 miRNAs expressed during morphogenesis and 7 miRNAs in the incisor cervical loop containing the stem cell niche. These miRNAs were mainly expressed in the dental epithelium. Conditional deletion of Dicer-1 in the epithelium (DcrK14−/−) resulted in rather mild but significant aberrations in tooth shape and enamel formation. The cusp patterns of the DcrK14−/− molar crowns resembled the patterns of both ancestral muroid rodents and mouse mutants with modulated signal pathways. In the DcrK14−/− incisors, longitudinal grooves formed on the labial surface and these were shown to result from ectopic budding of the progenitor epithelium in the cervical loop. In addition, ameloblast differentiation was impaired and resulted in deficient enamel formation in molars and incisors. To help the identification of candidate target genes of the selected tooth enriched miRNAs, we constructed a new ectodermal organ oriented database, miRTooth. The predicted targets of the selected miRNAs included several components of the main morphogenetic signal pathways regulating tooth development. Based on our findings we suggest that miRNAs modulate tooth morphogenesis largely by fine tuning conserved signaling networks and that miRNAs may have played important roles during tooth evolution. 相似文献
68.
Feroz Khan Haichuan Liu Aileen Reyes H. Ewa Witkowska Olga Martinez-Avila Li Zhu Wu Li Stefan Habelitz 《Biochimica et Biophysica Acta (BBA)/General Subjects》2013
Background
Enamel synthesis is a highly dynamic process characterized by simultaneity of matrix secretion, assembly and processing during apatite mineralization. MMP-20 is the first protease to hydrolyze amelogenin, resulting in specific cleavage products that self-assemble into nanostructures at specific mineral compositions and pH. In this investigation, enzyme kinetics of MMP-20 proteolysis of recombinant full-length human amelogenin (rH174) under different mineral compositions is elucidated.Methods
Recombinant amelogenin was cleaved by MMP-20 under various physicochemical conditions and the products were analyzed by SDS-PAGE and MALDI-TOF MS.Results
It was observed that mineral ions largely affect cleavage pattern, and enzyme kinetics of rH174 hydrolysis. Out of the five selected mineral ion compositions, MMP-20 was most efficient at high calcium concentration, whereas it was slowest at high phosphate, and at high calcium and phosphate concentrations. In most of the compositions, N- and C-termini were cleaved rapidly at several places but the central region of amelogenin was protected up to some extent in solutions with high calcium and phosphate contents.Conclusion
These in vitro studies showed that the chemistry of the protein solutions can significantly alter the processing of amelogenin by MMP-20, which may have significant effects in vivo matrix assembly and subsequent calcium phosphate mineralization.General significance
This study elaborates the possibilities of the processing of the organic matrix into mineralized tissue during enamel development. 相似文献69.
Study of the evolutionary enameloid/enamel transition suffers from discontinuous data in the fossil record, although a developmental
enameloid/enamel transition exists in living caudates, salamanders and newts. The timing and manner in which the enameloid/enamel
transition is achieved during caudate ontogeny is of great interest, because the caudate situation could reflect events that
have occurred during evolution. Using light and transmission electron microscopy, we have monitored the formation of the upper
tooth region in six successive teeth of a tooth family (position I) in Pleurodeles waltl from late embryos to young adult. Enameloid has only been identified in embryonic tooth I1 and in larval teeth I2 and I3. A thin layer of enamel is deposited later by ameloblasts on the enameloid surface of these teeth. From post-metamorphic
juvenile onwards, teeth are covered with enamel only. The collagen-rich enameloid matrix is deposited by odontoblasts, which
subsequently form dentin. Enameloid, like enamel, mineralizes and then matures but ameloblast participation in enameloid matrix
deposition has not been established. From tooth I1 to tooth I3, the enameloid matrix becomes ever more dense and increasingly comes to resemble the dentin matrix, although it is still
subjected to maturation. Our data suggest the absence of an enameloid/enamel transition and, instead, the occurrence of an
enameloid/dentin transition, which seems to result from a progressive slowing down of odontoblast activity. As a consequence,
the ameloblasts in post-metamorphic teeth appear to synthesize the enamel matrix earlier than in larval teeth. 相似文献
70.
During molar development from the cap to bell stage, the morphology of the enamel knots, inner dental epithelium, and epithelial-mesenchymal
junction dynamically changes, leading to the formation of multiple cusps. To study the basic histological features of this
morphogenetic change, we have investigated the cell arrangement, mitosis, and apoptosis simultaneously in the developing first
lower molar of the mouse by means of BrdU injection and immunostaining for P-cadherin, BrdU, and single-stranded DNA. At the
typical cap stage, the primary enamel knot shows a characteristic cell arrangement, absence of mitosis, and abundant apoptosis,
but also actively dividing cells at its lateral margins. Two secondary enamel knots then appear in the anterior part of the
tooth germ. One is completely non-proliferating, whereas the other contains dividing cells, indicating asymmetrical growth
of the inner dental epithelium. From this transitional stage to the early bell stage, additional minor BrdU-negative domains
appear, and at the same time, the cell arrangement in the inner dental epithelium rapidly changes to show regional differences.
Comparisons between the histology and the distribution of BrdU-positive cells have revealed that both the regionally different
cell rearrangement and the differential cell proliferation in the enamel knots and inner dental epithelium probably play a
significant role in multiple cusp formation. 相似文献