百岁以上老人跟骨骨密度和骨强度的相关性分析

目的研究广西巴马百岁以上女性老人的年龄、身高、体重、BMI与跟骨骨密度、骨强度之间的关系。方法采用定量超声骨密度测定仪,对广西巴马16名百岁以上女性老人的跟骨骨密度、骨强度进行测定,并记录相应年龄,同时行人工测量身高、体重、BMI指数,应用SPSS16.0软件分别计算年龄、身高、体重、BMI与跟骨骨密度、骨强度的pearson的相关系数。结果年龄、身高、体重、BMI均与百岁以上女性老人的跟骨骨密度、骨强度有相关关系,但相关性均无显著性(P0.05)。其中年龄、身高、体重与跟骨骨密度、骨强度呈负相关关系;BMI与跟骨骨密度、骨强度呈正相关关系,但相关性均无显著性(P0.05)。结论年龄、身高、体重、BMI均是广西巴马百岁以上女性老人骨密度、骨强度的影响因素,但相关性均无显著性,或需探讨新的评价指标衡量百岁以上女性老人的骨密度及骨强度,为百岁以上女性老人早期预防和诊断骨质疏松提供科学依据。     

Limb disparity and wing shape in pterosaurs

The limb proportions of the extinct flying pterosaurs were clearly distinct from their living counterparts, birds and bats. Within pterosaurs, however, we show that further differences in limb proportions exist between the two main groups: the clade of short-tailed Pterodactyloidea and the paraphyletic clades of long-tailed rhamphorhynchoids. The hindlimb to forelimb ratios of rhamphorhynchoid pterosaurs are similar to that seen in bats, whereas those of pterodactyloids are much higher. Such a clear difference in limb ratios indicates that the extent of the wing membrane in rhamphorhynchoids and pterodactyloids may also have differed; this is borne out by simple ternary analyses. Further, analyses also indicate that the limbs of Sordes pilosus, a well-preserved small taxon used as key evidence for inferring the extent and shape of the wing membrane in all pterosaurs, are not typical even of its closest relatives, other rhamphorhynchoids. Thus, a bat-like extensive hindlimb flight membrane, integrated with the feet and tail may be applicable only to a small subset of pterosaur diversity. The range of flight morphologies seen in these extinct reptiles may prove much broader than previously thought.     

Why fly? The possible benefits for lower mortality

In adult endotherms—birds and mammals—mortality rates are lower in flying than non-flying species. Rates vary with size, but allowing for this they are higher in penguins than flying birds, and in rodents than bats. These observations are most simply explained in terms of predation since flight, allowing movement in three dimensions, increases the chances of escape.
There are various problems in obtaining and comparing data on rates of mortality and this partly explains a wide scattering of points. Nevertheless the main results are statistically significant, mostly at P<0.001. Amongst birds, there are several other significant differences. Mortality rates are lower at lower latitudes, and in aquatic compared to terrestrial species, with cliff-nesters having lower rates than other aquatic birds and co-operative breeders than other terrestrial ones. No latitudinal effect was detected in mammals. The exceptionally low rates of mortality in bats and swifts are attributed to their being particularly hard to catch.     

The evolution of vertebrate flight

Flight–defined as the ability to produce useful aerodynamic forces by flapping the wings–is one of the most striking adaptations in vertebrates. Its origin has been surrounded by considerable controversy, due in part to terminological inconsistencies, in part to phylogenetic uncertainty over the sister groups and relationships of birds, bats and pterosaurs, and in part to disagreement over the interpretation of the available fossil evidence and over the relative importance of morphological, mechanical and ecological specializations. Study of the correlation between functional morphology and mechanics in contemporary birds and bats, and in particular of the aerodynamics of flapping wings, clarifies the mechanical changes needed in the course of the evolution of flight. This strongly favours a gliding origin of tetrapod flight, and on mechanical and ecological grounds the alternative cursorial and fluttering hypotheses (neither of which is at present well-defined) may be discounted. The argument is particularly strong in bats, but weaker in birds owing to apparent inconsistencies with the fossil evidence. However, study of the fossils of the Jurassic theropod dinosaur Archaeopteryx , the sister-group of the stem-group proto-birds, supports this view. Its morphology indicates adaptation for flapping flight at the moderately high speeds which would be associated with gliding, but not for the slow speeds which would be required for incipient flight in a running cursor, where the wingbeat is aerodynamically and kinematically considerably more complex. Slow flight in birds and bats is a more derived condition, and vertebrate flapping flight apparently evolved through a gliding stage.