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。     

广西化石猩猩牙尖釉质的日分泌率

作为现仅存于亚洲大陆的现生大猿,更新世时期猩猩曾广泛分布于东南亚大陆及华南地区,但其保留下来的化石材料主要为单颗牙齿。从牙齿形态、尺寸等外部特征的研究得出的关于猩猩的分类及演化问题的结论并未得到广泛一致的认同,而研究表明牙齿生长发育特征可作为系统分类研究的一个潜在工具。本研究选取了一批来自于中国广西更新世时期的猩猩牙齿化石,制作牙齿组织学切片,测量计算了其牙釉质日分泌率,结果显示广西化石猩猩牙尖釉质日分泌率在2.32-6.88μm/d之间,平均值约为4.61μm/d,从牙尖内部到表面,釉质日分泌率有增加趋势。此外,还将广西化石猩猩与其他现生大猿和现代人进行比较,以期从牙齿生长发育的角度为猩猩的演化和分类问题提供一点线索和证据。     

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.     

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。     

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。     

大荔颅骨在人类进化中的位置

本文将大荔颅骨的一系列形态特征与中国的直立人、欧洲和非洲的中更新世人、欧洲和亚洲的尼安德特人、中国和欧洲的早期现代人以及现生现代人的数据进行比较,发现可以归纳为几种状况。大荔颅骨:1)与其他中更新世颅骨比较一致,而与早期现代人相去较远;2)与早期和现生现代人一致或接近,显得比其他中更新世人进步;3)在中国早期现代人或现代人变异范围内,也在欧洲中更新世人变异范围内或与之接近,却与中国直立人相距较远;4)处于一般中更新世人与早期现代人之间的中间状态;5)处于中国直立人与中国早期现代人之间的中间位置,而且比较接近欧洲/非洲中更新世人;6)与东亚多数化石人比较一致,而与旧大陆西部中更新世化石人相去较远;7)与中国直立人显然不同,而与欧洲/非洲中更新世人更加接近;8)与非洲中更新世人接近,而与中国直立人和欧洲中更新世人差距较大;9)与大多数中更新世人不同,似乎是自身独有或罕见的。基于这样复杂的状况,作者提出,大荔颅骨既不属于直立人,也不属于海德堡人,表现为兼具东亚的直立人、欧洲和非洲中更新世人的特征,而且是这些共有特征与早期现代人部分特征的镶嵌体,可能比中国的直立人对中国现代人的形成做出过更大的贡献。     

人类牙齿齿冠和齿根分离两种技术方法对牙釉质厚度测量的影响

在基于计算机断层扫描技术（CT）和虚拟图像处理技术的灵长类牙齿测量学研究中,经常需要分离三维虚拟模型的齿冠和齿根,再进行后续测量工作,如计算机辅助的生物力学分析、釉质厚度测量等。而分离齿冠和齿根这一步骤,目前有多种方法,如,1)根据齿颈线切分齿冠,或2)人工建立基底平面切分齿冠。为了评估这两种不同的处理方式对后续的牙齿测量学上的影响,本文使用三维方法测量了82例化石和现代人类下颌后部牙齿的釉质厚度,包括南方古猿、早期人属、尼安德特人和现代人。使用配对t检验对比发现,两种方法得到的釉质厚度数值上没有显著差别,但随后进行的种间比较发现,使用基底平面切分齿冠的方法比较费时,更依赖于测量者的人工操作,并且可能弱化了物种间前臼齿绝对釉质厚度的差异,造成系统误差。其原因是对于前臼齿和前部牙齿等齿颈线形状不规则的标本,基底平面难以建立或误差较大。在未来对釉质厚度的种间差异的研究中,特别对齿颈线形状不规则的标本（如人类前部牙齿及猩猩、黑猩猩的牙齿等）,本文推荐使用齿颈线分离齿冠和齿根,测量和计算齿颈线之上的釉质厚度。釉质厚度有一定的分类学、功能形态学和系统发育学意义。本文积累了一批可供未来对比研究的原始数据,并且发现尼安德特人前臼齿的相对釉质厚度显著小于现代人,这与前人利用臼齿、犬齿所做的对比研究结果相同,支持了尼安德特人拥有较薄的相对釉质厚度这一观点。     

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。     

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。     

Three-dimensional primate molar enamel thickness

Molar enamel thickness has played an important role in the taxonomic, phylogenetic, and dietary assessments of fossil primate teeth for nearly 90 years. Despite the frequency with which enamel thickness is discussed in paleoanthropological discourse, methods used to attain information about enamel thickness are destructive and record information from only a single plane of section. Such semidestructive planar methods limit sample sizes and ignore dimensional data that may be culled from the entire length of a tooth. In light of recently developed techniques to investigate enamel thickness in 3D and the frequent use of enamel thickness in dietary and phylogenetic interpretations of living and fossil primates, the study presented here aims to produce and make available to other researchers a database of 3D enamel thickness measurements of primate molars (n=182 molars). The 3D enamel thickness measurements reported here generally agree with 2D studies. Hominoids show a broad range of relative enamel thicknesses, and cercopithecoids have relatively thicker enamel than ceboids, which in turn have relatively thicker enamel than strepsirrhine primates, on average. Past studies performed using 2D sections appear to have accurately diagnosed the 3D relative enamel thickness condition in great apes and humans: Gorilla has the relatively thinnest enamel, Pan has relatively thinner enamel than Pongo, and Homo has the relatively thickest enamel. Although the data set presented here has some taxonomic gaps, it may serve as a useful reference for researchers investigating enamel thickness in fossil taxa and studies of primate gnathic biology.     

Enamel thickness,microstructure and development in Afropithecus turkanensis

Afropithecus turkanensis, a 17-17.5 million year old large-bodied hominoid from Kenya, has previously been reported to be the oldest known thick-enamelled Miocene ape. Most investigations of enamel thickness in Miocene apes have been limited to opportunistic or destructive studies of small samples. Recently, more comprehensive studies of enamel thickness and microstructure in Proconsul, Lufengpithecus, and Dryopithecus, as well as extant apes and fossil humans, have provided information on rates and patterns of dental development, including crown formation time, and have begun to provide a comparative context for interpretation of the evolution of these characters throughout the past 20 million years of hominoid evolution. In this study, enamel thickness and aspects of the enamel microstructure in two A. turkanensis second molars were quantified and provide insight into rates of enamel apposition, numbers of cells actively secreting enamel, and the time required to form regions of the crown. The average value for relative enamel thickness in the two molars is 21.4, which is a lower value than a previous analysis of this species, but which is still relatively thick compared to extant apes. This value is similar to those of several Miocene hominoids, a fossil hominid, and modern humans. Certain aspects of the enamel microstructure are similar to Proconsul nyanzae, Dryopithecus laietanus, Lufengpithecus lufengensis, Graecopithecus freybergi and Pongo pygmaeus, while other features differ from extant and fossil hominoids. Crown formation times for the two teeth are 2.4-2.6 years and 2.9-3.1 years respectively. These times are similar to a number of extant and fossil hominoids, some of which appear to show additional developmental similarities, including thick enamel. Although thick enamel may be formed through several developmental pathways, most Miocene hominoids and fossil hominids with relatively thick enamel are characterized by a relatively long period of cuspal enamel formation and a rapid rate of enamel secretion throughout the whole cusp, but a shorter total crown formation time than thinner-enamelled extant apes.     

Taxonomic and functional aspects of the patterning of enamel thickness distribution in extant large-bodied hominoids

One of the few uncontested viewpoints in studies of enamel thickness is that the molars of the African apes, Pan and Gorilla, possess "thin" enamel, while Pongo and modern humans possess varying degrees of "thick" enamel, even when interspecific differences in overall body or tooth size are taken into account. Such studies focus primarily on estimates of the total volume of enamel relative to tooth size (i.e., "relative" enamel thickness), as this is thought to bear directly on questions concerning dietary proclivities and phylogenetic relationships. Only recently have studies shifted focus to examining differences in the distribution of enamel across the tooth crown, i.e., the patterning of enamel thickness, as this may contribute to more refined models of tooth function and dietary adaptations in extant hominoids. Additionally, this feature has been suggested to be a reliable indicator of taxonomic affinity in early hominins, though no study has specifically addressed whether species-specific patterns exist among known phena. The aims of this paper were to test more explicitly whether enamel thickness patterning provides valuable taxonomic, functional, and/or phylogenetic information for maxillary molars of large-bodied extant hominoids. A series of seven linear enamel thickness measurements was recorded in the plane of the mesial cusps in cross sections of a total of 62 maxillary molars of P. troglodytes, G. gorilla, P. pygmaeus, and H. sapiens to estimate the patterning of enamel thickness distribution. Results from a discriminant function analysis reveal that, overall, this trait reclassifies extant hominoid maxillary molars with 90% accuracy: 100% of extant Homo, 75. 0% of Pongo, 83.3% of Pan, and 66.7% of Gorilla are reclassified correctly, indicating that this feature possesses a strong taxonomic signal. Furthermore, differences in the structure of the enamel cap are evident among hominoids: modern humans differ from Pongo in possessing proportionally thicker enamel in areas of the crown associated with shearing activity; Pan molars are better designed than those of Gorilla for generating a greater component of crushing/grinding loads. Thus, African ape molars are structurally dissimilar, even though they are both considered to belong to a morphologically homogeneous "thin-enameled" group. Simple developmental mechanisms can be invoked to explain the sometimes subtle differences in the achievement of adult morphology. For instance, human and orangutan molar cusps possess a similar degree of enamel thickness, but the possibility exists that despite similarities in morphology, each species follows a different sequence of secretory activity of enamel to achieve the final, albeit similar, degree of enamel thickness. Such a finding would suggest that the shared possession of "thick" or "thin" enamel among species may be phylogenetically uninformative, as it would not represent a developmental synapomorphy.     

An examination of dental development in Graecopithecus freybergi (=Ouranopithecus macedoniensis)

This study examined enamel thickness and dental development in Graecopithecus freybergi (=Ouranopithecus macedoniensis), a late Miocene hominoid from Greece. Comparative emphasis was placed on Proconsul, Afropithecus, Dryopithecus, Lufengpithecus, and Gigantopithecus, fossil apes that vary in enamel thickness and patterns of development. In addition, comparisons were made with Paranthropus to investigate reported similarities in enamel thickness. Several sections of a right lower third molar were generated, from which enamel thickness and aspects of the enamel and dentine microstructure were determined. Data from parallel sections shed light on the effects of section obliquity, which may influence determination of both enamel thickness and crown formation time. Graecopithecus has relatively thick enamel, greater than any fossil ape but less than Paranthropus, with which it does show similarity in prism path and Hunter-Schreger band morphology. Aspects of enamel microstructure, including the periodicity and daily secretion rate, are similar to most extant and fossil apes, especially Afropithecus. Total crown formation time was estimated to be 3.5 years, which is greater than published values for modern Homo, similar to Pan, and less than Gigantopithecus. Data on dentine secretion and extension rates suggest that coronal dentine formation was relatively slow, but comparative data are very limited. Graecopithecus shares a crown formation pattern with several thick-enamelled hominoids, in which cuspal enamel makes up a very large portion of crown area, is formed by a large cell cohort, and is formed in less than half of the total time of formation. In Paranthropus, this pattern appears to be even more extreme, which may result in thicker enamel formed in an even shorter time. Developmental similarities between Paranthropus and Graecopithecus are interpreted to be parallelisms due to similarities in the mechanical demands of their diets.     

Perikymata spacing and distribution on hominid anterior teeth

We documented the spacing and distribution of perikymata on the buccal enamel surface of fossil hominin anterior teeth with reference to a sample of modern human and modern great ape teeth. A sample of 27 anterior teeth attributed to Australopithecus (5 to A. afarensis, 22 to A. africanus) and of 33 attributed to Paranthropus (6 to P. boisei, and 27 to P. robustus) were replicated and sputter-coated with gold to enable reflected light microscopy of their surface topography. Anterior teeth were then divided into 10 equal divisions of buccal crown height. The total perikymata count in each division of crown height was recorded using a binocular microscope fitted with a vernier micrometer eyepiece. Then the mean number of perikymata per millimeter was calculated for each division. Similar comparative data for a modern sample of 115 unworn human anterior teeth and 30 African great ape anterior teeth were collected from ground sections. Perikymata counts in each taxon (together with either known or presumed periodicities of perikymata) were then used to estimate enamel formation times in each division of crown height, for all anterior tooth types combined. The distributions of these estimates of time taken to form each division of crown height follow the same trends as the actual perikymata counts and differ between taxa in the same basic way. The distinction between modern African great apes and fossil hominins is particularly clear. Finally, we calculated crown formation times for each anterior tooth type by summing cuspal and lateral enamel formation times. Estimates of average crown formation times in australopiths are shorter than those calculated for both modern human and African great ape anterior teeth. The data presented here provide a better basis for exploring differences in perikymata spacing and distribution among fossil hominins, and provide the first opportunity to describe four specimens attributed to Homo in this context. Preliminary data indicate that differences may exist among the species attributed to early Homo, especially between Homo ergaster and Homo rudolfensis on the one hand, and Homo habilis sensu strico on the other.     

Molar enamel thickness and dentine horn height in Gigantopithecus blacki

Absolutely thick molar enamel is consistent with large body size estimates and dietary inferences about Gigantopithecus blacki, which focus on tough or fibrous vegetation. In this study, 10 G. blacki molars demonstrating various stages of attrition were imaged using high-resolution microtomography. Three-dimensional average enamel thickness and relative enamel thickness measurements were recorded on the least worn molars within the sample (n = 2). Seven molars were also virtually sectioned through the mesial cusps and two-dimensional enamel thickness and dentine horn height measurements were recorded. Gigantopithecus has the thickest enamel of any fossil or extant primate in terms of absolute thickness. Relative (size-scaled) measures of enamel thickness, however, support a thick characterization (i.e., not "hyper-thick"); G. blacki relative enamel thickness overlaps slightly with Pongo and completely with Homo. Gigantopithecus blacki dentine horns are relatively short, similar to (but shorter than) those of Pongo, which in turn are shorter than those of humans and African apes. Gigantopithecus blacki molar enamel (and to a lesser extent, that of Pongo pygmaeus) is distributed relatively evenly across the occlusal surface compared with the more complex distribution of enamel thickness in Homo sapiens. The combination of evenly distributed occlusal enamel and relatively short dentine horns in G. blacki results in a flat and low-cusped occlusal surface suitable to grinding tough or fibrous food objects. This suite of molar morphologies is also found to varying degrees in Pongo and Sivapithecus, but not in African apes and humans, and may be diagnostic of subfamily Ponginae.     

Tissue proportions and enamel thickness distribution in the early Middle Pleistocene human deciduous molars from Tighenif,Algeria

The present study of three human upper deciduous molars from the early Middle Pleistocene site of Tighenif, Algeria, constitutes the first microtomographic-based endostructural exploration of African fossil teeth likely representative of the Homo heidelbergensis morph. Comparative morphological observations and 2-3D measurements describing subtle tooth organization (crown tissue proportions) and enamel thickness topography (site-specific distribution and global patterning) indicate that their virtual extracted structural signature better fits the modern human, rather than the Neanderthal condition. Accordingly, we predict that the inner structural morphology of the deciduous molars from the Middle Pleistocene western European series better fits the primitive, and not the derived Neanderthal figures.