现代各主要人群额骨3D几何形态的对比

额骨是连接面颅和脑颅的重要头骨组成部分,关于现代各个人种的额骨形态是否存在明显的差别,这些人种额骨的基本形态如何,变异范围以及与其他人群的相似与差异等问题都尚未完全厘清。而额骨的很多特征由于技术手段的限制很难进行测量和准确的描述比较。鉴于这些问题,本文将采用基于三维表面半标志点的几何形态测量方法,研究东亚现代人额骨的表面形态及其变异范围,并与欧洲,东南亚,美洲,非洲以及澳洲的现代人群的额骨形态进行对比,为对比不同人群的形态研究建立基础数据。结果显示,额骨形态的变异主要表现在:1)额骨鳞部的额结节和正中矢状脊共同向前隆起或回缩以及相对额骨宽度;2)眉弓的粗壮程度,额结节的侧向发育程度和正中矢状脊的发育情况。为了进一步揭示中国现代人与其他人群在额骨形态上的关系,本文还探讨了额骨大小在不同人群中的差异。结果显示,东亚现代人和欧洲现代人额骨中心大小值的中位数最大,澳洲现代人的最小。东亚现代人的额骨形态与澳洲,欧洲和非洲均有非常显著的差异。为了检验额骨的形态是否与遗传距离一致,作者还对额骨形态距离和遗传距离做了相关性分析。结果显示,不同人群的额骨形态与其遗传距离呈显著的相关性,说明本研究结果中不同人群额骨形态上的差异大小可以在一定程度上反映其遗传距离,并可能进一步反映人群历史。东亚现代人的额骨平均形态在与各个人群比较过程中表现出一致性特征,可能在一定程度上反映了东亚现代人群的进化过程是相对独立的。未来额骨的三维几何形态测量可通过扩大标本数量进一步探讨不同性别和不同演化阶段之间的差异。     

How and why humans grow thin skulls: Experimental evidence for systemic cortical robusticity

To what extent is cranial vault thickness (CVT) a character that is strongly linked to the genome, or to what extent does it reflect the activity of an individual prior to skeletal maturity? Experimental data from pigs and armadillos indicate that CVT increases more rapidly in exercised juveniles than in genetically similar controls, despite the low levels of strain generated by chewing or locomotion in the neurocranium. CVT increases in these individuals appear to be a consequence of systemic cortical bone growth induced by exercise. In addition, an analysis of the variability in vault thickness in the genus Homo demonstrates that, until the Holocene, there has been only a slight, general decrease in vault thickness over time with no consistent significant differences between archaic and early anatomically modern humans from the Late Pleistocene. Although there may be some genetic component to variation in CVT, exercise-related, non-genetically heritable stimuli appear to account for most of the variance between individuals. The thick cranial vaults of most hunter-gatherers and early agriculturalists suggests that they may have experienced higher levels of sustained exercise relative to body mass than the majority of recent, post-industrial humans. © 1996 Wiley-Liss, Inc.     

Skull of Catopithecus browni,an early tertiary catarrhine

Fossil crania from quarry L-41, Fayum, Egypt, representing Catopithecus browni, a primate similar in size to callitrichids but with a catarrhine dental formula, provide the geologically earliest record of an anthropoidean skull. Catopithecus had postorbital closure developed to the stage seen in extant anthropoideans, with direct contact between zygomatic plate and maxillary tuber, isolating an anterior orbital fissure from the inferior orbital fissure. The auditory region also resembles that of later anthropoideans: The posterior carotid foramen is placed adjacent to the jugular fossa; a large promontory canal crosses the promontorium; and the annular ectotympanic is fused ventrally to the bulla. The incisors and canines show an assemblage of features found only among modern anthropoideans and adapoids. The face is characterized by a relatively deep maxilla, broad ascending wing of the premaxilla, and long nasal bones, yielding a moderate muzzle similar to that of Aegyptopithecus. The small braincase bears an anteriorly broad frontal trigon and a posteriorly developed sagittal crest. The mandibular symphysis is unfused even in mature adults. The encephalization quotient (EQ) probably falls within the range of Eocene prosimians, much lower than the EQs of Neogene anthropoideans. © 1996 Wiley-Liss, Inc.     

Cranial distinctiveness in the Apennine brown bear: genetic drift effect or ecophenotypic adaptation?

Molecular studies highlighted a strong genetic affinity between the remnant and isolated population of the Apennine brown bear and other southern European populations. Despite this genetic closeness a recent morphometric study revealed a marked phenotypic distinctiveness of the Apennine population, supporting the reinstatement of a distinct taxon (Ursus arctos marsicanus). By building upon previous morphological analyses, we adopted geometric morphometrics to better investigate the skull morphology of the Apennine brown bear with reference to the other, closely related southern European populations. Both skull shape and size differences confirmed the strong divergence of U. arctos marsicanus. In particular, the Apennine bears are characterized by an enlargement of the supraorbital apophysis and a larger distance across the zygomatic arches. Furthermore, our analyses highlighted significant shape differences of the first upper molar in the Apennine bears. Our results suggest that the Apennine bears underwent a rapid morphological change, possibly driven by genetic drift and local selective pressures. Because the greatest morphological differentiation is likely to be related to the muscles involved in mastication, we hypothesize that local selective pressures might be related to a shift in food habits, with highly reduced depredation and feeding on large carcasses in favour of vegetation and hard mast (beech nuts and acorns). These results suggest an adaptive distinctiveness of the Apennine bears, which should be carefully considered in any management and conservation action addressed to this highly endangered population. Although more in‐depth molecular studies are required to better assess the taxonomic and genetic status of the Apennine brown bear population, our study emphasizes the importance of morphological analyses as a complementary tool for a more thorough characterization of variation and divergence in endangered taxa. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.