Muscle strength and mineral densities in the mandible

Bone mineral density (BMD) in the femoral neck and lumbar spine was measured for 355 postmenopausal 48- to 56-year-old women and the BMD in five different regions in the mandible for 77. All 355 women were also classified according to the size of the masseter muscle. Both skeletal measures and the BMD of the buccal cortex distally from the foramen mentale were compared with the size of the masseter muscle. This study indicates that functional stress, caused by the masseter muscle, is involved in maintaining bone mineral density in edentulous regions of the mandible. Those individuals who are physically active or are bruxists may lose less mineral, after extractions of teeth, from those regions of the jaw bones where the muscles are attached.     

ADAPTIVE RADIATIONS,ECOLOGICAL SPECIALIZATION,AND THE EVOLUTIONARY INTEGRATION OF COMPLEX MORPHOLOGICAL STRUCTURES

The evolutionary integration of complex morphological structures is a macroevolutionary pattern in which morphogenetic components evolve in a coordinated fashion, which can result from the interplay among processes of developmental, genetic integration, and different types of selection. We tested hypotheses of ecological versus developmental factors underlying patterns of within‐species and evolutionary integration in the mandible of phyllostomid bats, during the most impressive ecological and morphological radiation among mammals. Shape variation of mandibular morphogenetic components was associated with diet, and the transition of integration patterns from developmental to within‐species to evolutionary was examined. Within‐species (as a proxy to genetic) integration in different lineages resembled developmental integration regardless of diet specialization, however, evolutionary integration patterns reflected selection in different mandibular components. For dietary specializations requiring extensive functional changes in mastication patterns or biting, such as frugivores and sanguivores, the evolutionary integration pattern was not associated with expected within‐species or developmental integration. On the other hand, specializations with lower mastication demands or without major functional reorganization (such as nectarivores and carnivores), presented evolutionary integration patterns similar to the expected developmental pattern. These results show that evolutionary integration patterns are largely a result of independent selection on specific components regardless of developmental modules.     

Changes in life-cycle strategies of Carabus problematicus over a range of altitudes in Northern England

ABSTRACT.

• 1 Mandible tip length has been used to estimate the age of individual C.problematicus Herbst caught over an altitude range of more than 700 m in northern England.
• 2 At 100 m the great majority of females laid eggs in the summer of their emergence as adults. The female life-cycle is predominantly annual and 24% only of the egg-bearing individuals were in their second year.
• 3 Above 250 m, most females did not reproduce until the summer of the year following emergence, giving a biennial life-cycle. 96% of egg-bearing females caught above 830 m were in their second year.
• 4 All the males caught during the breeding season at 100 m had emerged within that calendar year and it is concluded that the male life-cycle is annual at this altitude.
• 5 Above 250 m, 83% of the males caught during the breeding season were in their first calendar year, suggesting that recently emerged males may inseminate second year females and also that the male life-cycle is predominantly annual over the whole altitude range studied.
• 6 At the higher temperatures of the lowland site females not only produce eggs in the year of emergence, they also produce more eggs per individual than at the higher sites. Egg production depends on food intake which involves mandible wear and individuals at the lowland site have significantly higher rate of mandible wear than at the sites above 250 m.

     

中国人与澳大利亚人的颏孔高度

吴新智在1961年研究山顶洞人头骨时曾指出,下颌骨颏孔的相对高度在人类进化上有着一定的意义。尼人的这一指数比新人的低,新人化石的则比现代中国人的低。现代人这一方面的种族间比较则未见报道。本文提供资料以填补这方面的空缺。 本文所用材料是收藏于南京铁道医学院解剖教研室的,出自华东的现代中国人下颌骨和收藏于澳大利亚国立大学的采自木莱河流域的澳大利亚土著人下颌骨。中国标本的性别系根据同一个体的骨盆来判断;澳大利亚标本则由澳大利亚国立大学的人类学家桑恩博士参考同一个体的头骨来判断,作者在此表示感谢。     

Senescence in European Middle Pleistocene hominids: The Atapuerca evidence

The mandibular specimens AT-250 and AT-793 (individual IV) and AT-888 (individual XXI) from the Atapuerca Middle Pleistocene sample show a combination of traits interpreted as evidence of senescence. In order to explore age-related mandibular changes relevant to the interpretation of the Atapuerca hominids, the sample of known age and sex from Spitalfields (London) and the Neolithic sample from Abu Hureyra (Syria) were used as a baseline. Results obtained indicate that the occurrence of an enlarged and posteriorly located mental foramen, in association with high alveolar resorption in AT-250 and AT-888, support the hypothesis of senescence in individuals IV and XXI from the Atapuerca sample. The findings suggest that European Middle Pleistocene populations lived long enough to reach senescence. The age at death for Middle Pleistocene hominids and Neanderthals has previously been estimated at around 40–45 years in the oldest specimens. The appearance of senescence processes before this age is indicative of higher rates of morphological aging in the clade which gave rise to Neanderthals. The anatomical significance of ageing features when considered in the context of craniofacial remodelling can help in the understanding of the taxonomic status of these morphological traits.     

绿豆象幼虫虫龄的划分及末龄幼虫头部形态和感器观察

【目的】明确绿豆象Callosobruchus chinensis幼虫的龄期,了解其末龄幼虫头部感受器的种类、形态和分布。【方法】测量绿豆象幼虫体长、头壳宽和上颚宽,根据所得数据的频次分布图、关系拟合结果和戴氏法则确定绿豆象最佳分龄指标,明确幼虫虫龄数,并利用Crosby生长法则和线性回归的方法进行验证;采用扫描电镜对末龄幼虫头部形态及感受器进行观察。【结果】绿豆象体长、头壳宽和上颚宽的频次分布均呈显著的4个峰,因此推断绿豆象幼虫为4个虫龄。各龄的体长变幅分别为1.581～2.556, 2.406～3.381, 3.381～4.281和4.206～4.881 mm,头壳宽度变幅分别为0.444～0.689, 0.654～0.934, 0.934～1.179和1.144～1.389 mm,上颚宽变幅分别为0.080～0.256, 0.234～0.344, 0.322～0.542和0.542～0.652 mm。体长、头壳宽和上颚宽均符合戴氏法则和Crosby生长法则,并呈现明显的线性关系,因此体长、头壳宽和上颚宽可作为绿豆象幼虫龄期划分的重要指标。头壳宽的Crosby指数均小于体长和上颚宽...     

我国12种蚊幼虫上颚形态和鉴别特征的研究

本文对8种库蚊和按蚊、伊蚊、阿蚊及杵蚊各属代表种的4龄幼虫上颚进行扫描电镜观察.概述了上颚的外部形态,并提出了各蚊种的鉴别特征.指出幼虫上颚具有显著的种间差异,具有重要的分类学意义,讨论了上颚的结构与功能的关系.通过对上颚结构和取食方式的比较研究,从生物学角度,提出蚊科进化关系.     

Loss of molar occlusion and mandibular morphology in adults in an ancient human population consuming a coarse diet

The purpose of the study is to investigate the link between number of molar teeth retained in occlusion and mandibular morphology in adults in an ancient, high dental wear human population. The study material comprises skeletons from Mediaeval Wharram Percy, England (N = 50 female, 69 male adults). It was hypothesized that adults retaining fewer occluding molars would show reduction in mandibular dimensions, particularly in the ascending ramus and gonial regions where the main muscles of mastication have their insertions. Molar occlusal status is assessed using the concept of functional units. Mandibular morphology is assessed using a suite of ten linear measurements plus the mandibular angle. Results show no evidence for any association between number of molars retained in occlusion and mandibular angle. There was an association between mandibular size and number of molars retained in occlusion, with smaller mandibular dimensions in those retaining fewer occluding molars. Some measurements were affected more than others so that there was also some shape alteration. Alteration of mandibular dimensions was more clearly demonstrable in females than in males. Only in females could significant reduction in the ascending ramus and gonial regions be demonstrated. Reasons for the apparent difference in response to loss of molar occlusion between male and female mandibles are unclear, but sex differences in bony metabolism mediated by hormonal factors may be implicated. Results suggest that care should be exercised when including mandibles from individuals showing loss of molar occlusion in morphological studies. Am J Phys Anthropol 152:383–392, 2013. © 2013 Wiley Periodicals, Inc.