广西化石猩猩牙齿釉质厚度研究

华南和东南亚发现大量更新世的猩猩牙齿化石。本研究应用CT扫描三维重建的技术方法研究了广西更新世化石猩猩牙齿釉质厚度,并与现生类人猿、现代人、化石类人猿以及早期人类进行比较分析。结果显示:广西猩猩同类牙齿的釉质厚度与牙齿大小相关性很小;臼齿和前臼齿釉质厚度在上下颌之间不存在显著性差异;来自广西不同地区的猩猩化石牙釉质厚度无显著差异。与早期人科成员相比,广西猩猩的牙釉质相对较薄,平均与相对釉质厚度值都明显小于南方古猿、傍人。与早期人属相比,小于直立人、尼人以及非洲和欧洲的早期人属化石。与现代人和现生灵长类相比,广西化石猩猩釉质厚度明显大于大部分猴类和非洲大猿;平均釉质厚度稍大于现生猩猩,而与现代人更为接近;相对釉质厚度小于现代人,而与现生猩猩差异不大,都属于偏厚型釉质。本文讨论了釉质厚度与系统分类演化、食性适应的相关问题,作者推测釉质厚度可能是物种的特征属性,与牙齿功能适应有密切关联。     

华南化石猩猩前部牙齿釉面横纹与牙冠形成时间研究

釉面横纹的分布与数目可以反映牙齿生长发育的时间和速率变化, 在化石研究中能为复原个体生活史提供重要依据。本研究运用扫描电子显微镜观察华南化石猩猩门齿、犬齿釉面横纹分布与数目, 并估算门齿和犬齿牙冠形成时间, 结果如下: 牙冠从牙尖至牙颈方向釉面横纹分布密度有疏密变化, 牙尖釉面横纹密度小于10条/mm, 中间至牙颈釉面横纹密度较尖部增大, 大约10-15条/mm; 犬齿釉面横纹数目多于门齿, 雄性犬齿釉面横纹数目多于雌性; 根据釉面横纹计数及其生长周期的组织切片观察结果, 估算门齿牙冠形成时间大约为2.97-6.66年, 犬齿雄性长于雌性, 分别为6.25-11.31年和4.28-7.29年。与一些古猿、早期人类、现代人以及现生大猿比较, 华南化石猩猩釉面横纹整体密度稍大于南方古猿和傍人, 小于黑猩猩、大猩猩、现代人和禄丰古猿; 除侧门齿外, 华南化石猩猩釉面横纹数目明显多于南方古猿、傍人和现代人, 与大猩猩接近; 华南猩猩前部牙齿牙冠形成时间与现生大猿、禄丰古猿差别不大, 与现生猩猩最相近, 长于南方古猿和傍人。     

巨猿牙齿釉质厚度及对食性适应与系统演化的意义

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。     

中国更新世猩猩类牙齿化石的测量研究及其分类学意义

近些年,我国华南地区不断有猩猩类牙齿化石的发现,这些材料对于研究东亚地区大型类人猿的演化、灭绝及其环境变迁具有重要意义.本文基于猩猩类牙齿化石的测量和统计分析,结合形态学研究,尝试探讨它们的分类学意义及演化趋势等.经过分析比较得出以下认识:我国更新世猩猩与印尼的亚化石猩猩和现生猩猩在颊侧牙齿大小上存在显著性差异,依次呈减小趋势.在形态特征方面,亦存在一些明显差别.据此认为我国更新世猩猩建立魏氏亚种(Pongo pygmaeus weidenreichi)的观点是合理的.     

禄丰古猿(Lufengpithecus lufengensis)牙齿釉质生长线与个体发育问题研究

运用扫描电子显微镜,对4枚禄丰古猿牙齿（恒齿）的釉质结构进行了观察研究。发现：禄丰古猿牙齿釉质表面有明显的釉面横纹结构;釉面横纹的密度向牙颈方向逐渐增大;观察记数了4枚牙齿的釉面横纹数,进而推算出牙冠的形成时间和年龄。与化石人科成员、现代人及现生大猿比较,禄丰古猿牙冠发育模式及时间,与南方古猿纤细种比较接近或相似,明显长于南方古猿粗壮种,有别于现生大猿。     

禄丰古猿牙齿釉质生长线与个体发育问题研究

运用扫描电子显微镜,对４枚禄丰古猿牙齿（恒齿）釉质结构进行了观察研究,发现：禄丰古猿牙齿釉质表面有明显的釉面横纹结构;釉面横纹的密度向牙颈方向逐渐增大;观察记数了４枚牙齿的釉面横纹数,进而推算出牙冠的形成时间和年龄。与化石人科成员,现代人及现生大猿比较,禄丰古猿牙冠发育模式及时间,与南方古猿纤细种比较接近或相似,明显长于南方古猿粗壮种,有别于现生大猿。     

巨猿(Gigantopithecus blacki)牙齿釉质的超微结构

本文用扫描电镜研究了现代人牙齿和产自广西柳城县社冲村楞寨山巨猿洞,更新世早期的巨猿牙齿的超微结构。巨猿牙齿的表层釉质是Ⅰ型釉柱结构,厚度约为50－60μm,表层下牙尖中心区为Ⅰ型釉柱,其余为Ⅲa型及少量Ⅱ型釉柱结构。现代人牙表层釉质亦为Ⅰ型釉柱结构,厚度小于10μm,表层下,牙尖中心区处为Ⅰ型釉柱,其余为Ⅲa和Ⅲb型以及少量Ⅲ型釉柱。可以认为,这种差别具有分类学上的意义。此外,本文从研究方法上提出,研究釉柱横切面构造的最合适部位为牙尖部位的咬合面。     

我国更新世长臂猿化石的初步研究

通过对广西长臂猿牙齿化石的形态观察,更新世时期至少有两种长臂猿生存于我国,即Hylobates concolor,Hylobates hoolock,这两种均系我国现生长臂猿种类。其中黑长臂猿牙齿的性状,在不同时期的变化甚小,保留了较多的祖先型。由于长臂猿对森林环境的依赖,使它成为探讨更新世时期森林环境的最好指示动物之一。它们在时间分布上,从更新世早期一直延续到全新世。在空间分布上,都较现生者更为广泛。     

广西崇左更新世长臂猿化石新材料（英文）

近年,在对广西崇左地区第四纪洞穴堆积调查的过程中,从年代贯穿更新世的8个地点采集到了33颗长臂猿游离牙齿化石。记述了这些新发现的长臂化石,并初步确定了其分类位置。形态和测量的对比表明,这些牙齿不超过现生长臂猿种内变异的范围,且都可以归入一个种内。它们与冠长臂猿属(Nomascus)共有的特征组合表明,这些化石可以归入该属。这些特征包括:上臼齿相对宽,舌侧齿带及唇侧齿带痕迹保留率高;M3长度几乎与M1相等;下臼齿狭窄,并保留唇侧齿带退化痕迹。崇左地区的化石长臂猿的臼齿平均比冠长臂猿属中现生种类稍显大。但是崇左地区的游离牙齿化石材料提供的证据并不足以支持将其归入该属中的某一具体种类。与中国南方更新世其他同时代的大型猿类猩猩(Pongo)和巨猿(Gigantopithecus)不同,长臂猿的牙齿大小并没有随时间发生变化。尽管冠长臂猿属在现今的崇左地区并没有分布,但是在历史时期该属曾经广泛分布于中国南方地区。     

两广部分地区猩猩化石的研究

本文对广东罗定、云浮及广西等地的猩猩牙齿化石进行了宏观及微观的形态观察。认为猩猩牙齿咬合面除有较多的褶皱外,大多数标本上还有明显的生长线。化石猩猩牙齿与现生种的相比.牙齿的生长线后者不如前者显著;牙齿的大小是后者小于前者。这些现象表明Hooijer(1948)提出的 Pongo Pygmaeus weidenreichi可以成立。     

Molar crown formation in the Late Miocene Asian hominoids, Sivapithecus parvada and Sivapithecus indicus

During the past decade, studies of enamel development have provided a broad temporal and geographic perspective on evolutionary developmental biology in Miocene hominoids. Here we report some of the first data for molar crown development in one hominoid genus, Sivapithecus. The data are compared to a range of extant and extinct hominoids. Crown formation times (CFTs), daily rates of enamel secretion (DSR), Retzius line number and periodicity, and relative enamel thickness (RET) were calculated in a mandibular first molar of Sivapithecus parvada and a maxillary first molar of Sivapithecus indicus from the Siwalik sequence of Pakistan. A CFT of 2.40 years for the protoconid of S. parvada and 2.25 years for the protocone of S. indicus lie within the range of first molar (M1) formation times for the majority of Miocene hominoids (1.96-2.40 years, excluding Proconsul heseloni), and are similar to an M(1) from Gorilla (2.31 years) and M(1)s from Pan (2.22-2.39 years). This is unlike the longer CFTs in modern humans, which appear to be linked with their extended growth period. In contrast to extant great apes and humans, daily rates of enamel secretion are rapid in the Sivapithecus M1s during the early stages of growth, which seems to be a common pattern for most Miocene apes. The rapid accumulation of cuspal enamel in the Sivapithecus molars produced thicker enamel than either Pan or Gorilla in a comparable period of time. Future studies on larger samples of living and fossil hominoids are needed to clarify trends in crown development, which may be better understood in the context of life history strategies coupled with good data on body mass and brain size.     

Developmental Aspects of Sexual Dimorphism in Hominoid Canines

We examined the histology of canine teeth in extant hominoids and provided a comparative database on several aspects of canine development. The resultant data augment the known pattern of differences in aspects of tooth crown formation among great apes and more importantly, enable us to determine the underlying developmental mechanisms responsible for canine dimorphism in them. We sectioned and analyzed a large sample (n = 108) of reliably-sexed great ape mandibular canines according to standard histological techniques. Using information from long- and short-period incremental markings in teeth, we recorded measurements of daily secretion rates, periodicity and linear enamel thickness for specimens of Pan troglodytes, Gorilla gorilla, Pongo pygmaeus and Homo sapiens. Modal values of periodicities in males and females, respectively, are: Pan 7/7; Gorilla 9/10; Pongo 10/10; and Homo 8/8. Secretion rates increase from the inner to the outer region of the enamel cap and decrease from the cuspal towards the cervical margin of the canine crown in all great ape species. Female hominoids tend to possess significantly thicker enamel than their male counterparts, which is almost certainly related to the presence of faster daily secretion rates near the enamel-dentine junction, especially in Gorilla and Pongo. Taken together, these results indicate that sexual differences in canine development are most apparent in the earlier stages of canine crown formation, while interspecific differences are most apparent in the outer crown region. When combined with results on the rate and duration of canine crown formation, the results provide essential background work for larger projects aimed at understanding the developmental basis of canine dimorphism in extant and extinct large-bodied hominoids and eventually in early hominins.     

Built to last: The structure,function, and evolution of primate dental enamel

The teeth of every primate, living and extinct, are covered by a hard, durable layer of enamel. This is not unique: Almost all mammals have enamel-covered teeth. In addition, all of the variations in enamel structure that occur in primates are also found in other groups of mammals. Nevertheless, the very complexity of enamel and the variation we see in it on the teeth of living and fossil primates raise questions about its evolutionary significance. Is the complex structure of primate enamel adaptive? What, if anything, does enamel structure tell us about primate phylogeny? To answer these questions, we need to look more closely at the characteristics of prismatic enamel in primates and at the distribution of those characteristics, both in relation to our knowledge of primate dental function and feeding ecology and from a phylogenetic perspective.     

Pig enamel revisited – Incremental markings in enamel of wild boars and domestic pigs

The nature and periodicity of incremental markings in pig enamel is currently debated. To broaden the basis for a correct interpretation of growth marks in pig enamel, we analyzed their periodicity in teeth of wild boars and domestic pigs. For that, the numbers of enamel incremental markings were recorded in ground sections and compared with crown formation times for the respective teeth derived from literature data on tooth development and eruption in Sus scrofa. Our study revealed that laminations with a daily periodicity are the dominant incremental feature of pig enamel. In wild boar M₃s, daily enamel secretion (apposition) rates ranged between a minimum of 6.1?µm in the inner and a maximum of 30.6?µm in the outer enamel.Long-period (supra-daily) incremental markings were present as perikymata at the outer enamel surface (OES). Contrary to the situation in primate enamel, in pig enamel the long-period incremental lines terminating in perikyma grooves were mostly structurally indistinguishable from the daily laminations. Typically, five sub-daily increments were present between successive laminations. The incremental pattern in pig enamel can be misinterpreted if the laminations are mistaken for long-period markings (striae of Retzius) and the sub-daily growth marks for daily prism cross-striations. The findings of the present study demonstrate the critical importance of correctly characterizing the incremental markings and their periodicity in enamel, and caution against an uncritical transfer of the interpretation of the nature of incremental markings in primate enamel to other mammalian taxa.     

On thick and thin enamel in hominoids

Martin (1983, 1985) reviewed the significance of enamel thickness in hominoid evolution. He studied cut faces of hominoid teeth using the scanning electron microscope and related enamel prism packing patterns to both enamel formation rates and enamel thickness, although he did not present primary data on formation rates, which he summarised as being either “fast” or “slow.” Martin concluded that thick enamel formed at a fast rate represented the ancestral condition in the human and great ape clade. Thin enamel in African apes reflected a secondary reduction in secretion rates, with outer enamel being formed at a slow rate. The present study on ground sections of great ape and human teeth, using polarised light microscopy, was designed to measure the spacing between incremental growth lines in enamel, including striae of Retzius and prism cross striations, to determine rates of enamel formation in hominoids. Measurements on stria spacing showed that striae generally diverged as they passed outwards through enamel in all taxa. Cross-striation spacings also increased from inner to outer enamel. Secretion rates did not fall into two exclusive categories but varied, giving a spectrum of values generally increasing from within outwards at any one crown level and reducing in cervical enamel. There was no evidence for a reduction in enamel formation rates in outer enamel among African apes. These findings cast doubt on the proposition that the common ancestor of great apes and man had thick enamel formed at a fast rate. It is possible that thin enamel was the primitive condition, in which case thick enamel in humans and in Sivapithecus is derived, suggesting that thick enamel on low cusped teeth evolved on more than one occasion.     

Enamel hypoplasia in deciduous teeth of great apes: do differences in defect prevalence imply differential levels of physiological stress?

This paper presents new data on enamel hypoplasia in the deciduous canine teeth of great apes. The enamel defect under consideration is known as localized hypoplasia of primary canines (LHPC), and is characterized by an area of thin or missing enamel on the labial surface of deciduous canine teeth (Skinner [1986a] Am. J. Phys. Anthropol. 69:59-69). Goals of this study are: 1) to determine if significant differences in the frequency of LHPC occur among three genera of great apes, and 2) to evaluate variation in LHPC prevalence among great apes as evidence of differential physiological stress. Infant and juvenile apes with deciduous teeth were examined at the Cleveland Museum of Natural History (n = 100) and at the Smithsonian Institution, National Museum of Natural History (n = 36). Deciduous teeth were observed under oblique incandescent light, with the naked eye and with a 10x hand lens. Enamel hypoplasia was scored using Federation Dentaire International (FDI)-Defects of Dental Enamel (DDE) standards. Hypoplasias were recorded by drawing defect location and size on a dental chart, and by measuring defect size and location with Helios needlepoint dial calipers. The prevalence of LHPC is reported by genus and sex, using two approaches: 1) the frequency of affected individuals-those having one or more deciduous canine teeth scored positive for LHPC; and 2) the number of canine teeth scored positive for LHPC as a percentage of all canine teeth observed. Variation in defect size and location will be described elsewhere. Localized hypoplasia of primary canine teeth was found in 62.5% of 128 individual apes, and in 45.5% of 398 great ape deciduous canines. As in humans, LHPC is the most common form of enamel hypoplasia in deciduous teeth of great apes, while LEH is rare or absent. The distribution and pattern of expression of LHPC in great apes is similar to that described in humans: side differences are not significant, but mandibular canines exhibit the defect two to five times more often than maxillary canine teeth. Differences in LHPC prevalence by sex are small and not significant. Intergeneric differences are large and non-random: chimpanzees (Pan) exhibit a significantly lower frequency of LHPC (22%, n = 50) by individual count, than either the orangutan (Pongo, 88.0%, n = 25) or the gorilla (Gorilla, 88.7%, n = 53). Tooth count prevalences exhibit a similar pattern of variation and are also statistically significant. These findings suggest that large bodied great apes (gorilla and orangutan) may be under greater physiological stress during perinatal and early postnatal development than the chimpanzee. The size, position, and timing of LHPC lesions are currently under analysis and may yield more insight into the etiological origin of this enamel defect.     

A Systematic Study on Tooth Enamel Microstructures of Lambdopsalis bulla (Multituberculate,Mammalia) - Implications for Multituberculate Biology and Phylogeny

Tooth enamel microstructure is a reliable and widely used indicator of dietary interpretations and data for phylogenetic reconstruction, if all levels of variability are investigated. It is usually difficult to have a thorough examination at all levels of enamel structures for any mammals, especially for the early mammals, which are commonly represented by sparse specimens. Because of the random preservation of specimens, enamel microstructures from different teeth in various species are often compared. There are few examples that convincingly show intraspecific variation of tooth enamel microstructure in full dentition of a species, including multituberculates. Here we present a systematic survey of tooth enamel microstructures of Lambdopsalis bulla, a taeniolabidoid multituberculate from the Late Paleocene Nomogen Formation, Inner Mongolia. We examined enamel structures at all hierarchical levels. The samples are treated differently in section orientations and acid preparation and examined using different imaging methods. The results show that, except for preparation artifacts, the crystallites, enamel types, Schmelzmuster and dentition types of Lambdopsalis are relatively consistent in all permanent teeth, but the prism type, including the prism shape, size and density, may vary in different portions of a single tooth or among different teeth of an individual animal. The most common Schmelzmuster of the permanent teeth in Lambdopsalis is a combination of radial enamel in the inner and middle layers, aprismatic enamel in the outer layer, and irregular decussations in tooth crown area with great curvature. The prism seam is another comparably stable characteristic that may be a useful feature for multituberculate taxonomy. The systematic documentation of enamel structures in Lambdopsalis may be generalized for the enamel microstructure study, and thus for taxonomy and phylogenetic reconstruction, of multituberculates and even informative for the enamel study of other early mammals.     

Structural Morphology of Molars in Large Mammalian Herbivores: Enamel Content Varies between Tooth Positions

The distribution of dental tissues in mammalian herbivores can be very different from taxon to taxon. While grazers tend to have more elaborated and complexly folded enamel ridges, browsers have less complex enamel ridges which can even be so far reduced that they are completely lost. The gradient in relative enamel content and complexity of structures has so far not been addressed within a single species. However, several studies have noted tooth position specific wear rates in small mammals (rabbits, guinea pigs) which may be related to individual tooth morphology. We investigate whether differentiated enamel content by tooth position is also to be found in large herbivores. We use CT-scanning techniques to quantify relative enamel content in upper and lower molar teeth of 21 large herbivorous mammal species. By using a broad approach and including both perissodactyls and artiodactyls, we address phylogenetic intraspecific differences in relative enamel content. We find that enamel is highly unevenly distributed among molars (upper M1, M2, M3 and lower m1, m2, m3) in most taxa and that relative enamel content is independent of phylogeny. Overall, relative enamel content increases along the molar tooth row and is significantly higher in lower molars compared to upper molars. We relate this differential enamel content to prolonged mineralisation in the posterior tooth positions and suggest a compensatory function of m3 and M3 for functional losses of anterior teeth.