A transitional snake from the Late Cretaceous period of North America

Snakes are the most diverse group of lizards, but their origins and early evolution remain poorly understood owing to a lack of transitional forms. Several major issues remain outstanding, such as whether snakes originated in a marine or terrestrial environment and how their unique feeding mechanism evolved. The Cretaceous Coniophis precedens was among the first Mesozoic snakes discovered, but until now only an isolated vertebra has been described and it has therefore been overlooked in discussions of snake evolution. Here we report on previously undescribed material from this ancient snake, including the maxilla, dentary and additional vertebrae. Coniophis is not an anilioid as previously thought a revised phylogenetic analysis of Ophidia shows that it instead represents the most primitive known snake. Accordingly, its morphology and ecology are critical to understanding snake evolution. Coniophis occurs in a continental floodplain environment, consistent with a terrestrial rather than a marine origin; furthermore, its small size and reduced neural spines indicate fossorial habits, suggesting that snakes evolved from burrowing lizards. The skull is intermediate between that of lizards and snakes. Hooked teeth and an intramandibular joint indicate that Coniophis fed on relatively large, soft-bodied prey. However, the maxilla is firmly united with the skull, indicating an akinetic rostrum. Coniophis therefore represents a transitional snake, combining a snake-like body and a lizard-like head. Subsequent to the evolution of a serpentine body and carnivory, snakes evolved a highly specialized, kinetic skull, which was followed by a major adaptive radiation in the Early Cretaceous period. This pattern suggests that the kinetic skull was a key innovation that permitted the diversification of snakes.     

颅骨标本制作一例

介绍由头颅制作颅骨标本的一种处理方法。将头颅加热浸泡、脱脂、漂白处理后,用泡沫塑料和乙酸乙酯所配制成的溶液涂刷。该法制作过程简单、方便,各溶液配制容易,且毒性小。     

黄颡鱼头骨的研究

黄颡鱼头骨共有126块,无顶骨、后耳骨和下鳃盖骨,有续软骨存在.犁骨、前颌骨、齿骨上都具铺石状牙齿,上颌骨、腭骨不具齿而成棒状小骨支持触须.舌颌骨、方骨、中翼骨、外翼骨发育良好.前鳃盖骨失去鳃盖作用而参与悬器的形成.     

Resistance to mantle flow inferred from the electromagnetic strike of the Australian upper mantle

Seismic anisotropy is thought to result from the strain-induced lattice-preferred orientation of mantle minerals, especially olivine, owing to shear waves propagating faster along the a-axis of olivine crystals than along the other axes. This anisotropy results in birefringence, or 'shear-wave splitting', which has been investigated in numerous studies. Although olivine is also anisotropic with respect to electrical conductivity (with the a-axis being most conductive), few studies of the electrical anisotropy of the upper mantle have been undertaken, and these have been limited to relatively shallow depths in the lithospheric upper mantle. Theoretical models of mantle flow have been used to infer that, for progressive simple shear imparted by the motion of an overriding tectonic plate, the a-axes of olivine crystals should align themselves parallel to the direction of plate motion. Here, however, we show that a significant discrepancy exists between the electromagnetic strike of the mantle below Australia and the direction of present-day absolute plate motion. We infer from this discrepancy that the a-axes of olivine crystals are not aligned with the direction of the present-day plate motion of Australia, indicating resistance to deformation of the mantle by plate motion.     

短尾拟鲿头骨的研究

短尾拟鲿头骨结构中无顶骨、后耳骨、下鳃盖骨,有续软骨存在;犁骨、前颌骨;齿骨上密生铺石状牙齿;上颌骨和腭骨分别特化成粒状和棒状小骨,用以支持触须;舌颌骨、方骨、中翼骨、外翼骨发育良好;前鳃盖骨失去鳃盖作用而参与悬器形成;上枕骨具成对的三叉神经叉脊支神经孔。     

数字化钛网在颅骨缺损修补中的应用

目的 探讨运用数字化钛网修补颅骨缺损的临床应用及推广价值.方法 应用钛网片行颅骨修补术22例,根据其缺损的具体形态,采用数字化三维成像技术,制作个体化钛网修补材料,施行颅骨缺损修补.结果 数字化塑形人工颅骨修补,手术时间短,省时省力,外形满意率高.结论 数字化钛网修补颅骨缺损,塑形效果好,手术操作过程简捷,具有应用及推广价值.     

Meteoritic dust from the atmospheric disintegration of a large meteoroid

Much of the mass of most meteoroids entering the Earth's atmosphere is consumed in the process of ablation. Larger meteoroids (> 10 cm), which in some cases reach the ground as meteorites, typically have survival fractions near 1-25 per cent of their initial mass. The fate of the remaining ablated material is unclear, but theory suggests that much of it should recondense through coagulation as nanometre-sized particles. No direct measurements of such meteoric 'smoke' have hitherto been made. Here we report the disintegration of one of the largest meteoroids to have entered the Earth's atmosphere during the past decade, and show that the dominant contribution to the mass of the residual atmospheric aerosol was in the form of micrometre-sized particles. This result is contrary to the usual view that most of the material in large meteoroids is efficiently converted to particles of much smaller size through ablation. Assuming that our observations are of a typical event, we suggest that large meteoroids provide the dominant source of micrometre-sized meteoritic dust at the Earth's surface over long timescales.     

颅骨图像的阈值分割算法研究

针对颅骨CT图像中灰度值范围变化较大的特点,阐述了两种图像的分割方法,一种是基于边缘信息的分割,一种是基于区域信息的图像分割,提出了在颅骨CT图像分割中采用基于区域的阈值分割算法,并通过软件编程实验证明了它具有算法简单、识别效果好、效率高的特点．     

Myotoxic activity of a Gln-49 phospholipase A_2 from Agkistrodon blomhoffii ussurensis snake venom

A novel myotoxic protein phospholipase A2(PLA2), denoted as Gln49-PLA2, has been isolated from snake venom of Agkistrodon blomhoffii ussurensis, which has weak lethal effect and apparent anticoagulant activity, but lacks the PLA2 and hemorrha-genic activity. Gln49-PLA2 obviously increases of plasma creatine-kinase (CK) upon intramuscular injection in mice, suggesting that it may induce a dose-dependent myonecrosis. Histological studies also reveal morphological changes in mouse skeletal muscles, including extensive myonecrosis, hemorrhage and neutrophil infiltration in the treated animals. The myotoxic ability induced by Gln49-PLA2 can be partially inhibited by heparin.     

Evolutionary origin and development of snake fangs

Many advanced snakes use fangs-specialized teeth associated with a venom gland-to introduce venom into prey or attacker. Various front- and rear-fanged groups are recognized, according to whether their fangs are positioned anterior (for example cobras and vipers) or posterior (for example grass snakes) in the upper jaw. A fundamental controversy in snake evolution is whether or not front and rear fangs share the same evolutionary and developmental origin. Resolving this controversy could identify a major evolutionary transition underlying the massive radiation of advanced snakes, and the associated developmental events. Here we examine this issue by visualizing the tooth-forming epithelium in the upper jaw of 96 snake embryos, covering eight species. We use the sonic hedgehog gene as a marker, and three-dimensionally reconstruct the development in 41 of the embryos. We show that front fangs develop from the posterior end of the upper jaw, and are strikingly similar in morphogenesis to rear fangs. This is consistent with their being homologous. In front-fanged snakes, the anterior part of the upper jaw lacks sonic hedgehog expression, and ontogenetic allometry displaces the fang from its posterior developmental origin to its adult front position-consistent with an ancestral posterior position of the front fang. In rear-fanged snakes, the fangs develop from an independent posterior dental lamina and retain their posterior position. In light of our findings, we put forward a new model for the evolution of snake fangs: a posterior subregion of the tooth-forming epithelium became developmentally uncoupled from the remaining dentition, which allowed the posterior teeth to evolve independently and in close association with the venom gland, becoming highly modified in different lineages. This developmental event could have facilitated the massive radiation of advanced snakes in the Cenozoic era, resulting in the spectacular diversity of snakes seen today.     

竹叶青(Trimeresurus stejnegeri)蛇毒五种磷脂酶A2的分离纯化和氨基酸序列分析

用超细Sephadex G-75凝胶色谱和C4反相高效液相色谱从竹叶青（Trimeresurus stejnegeri）蛇毒中分离纯化5种磷脂酶A2,并分别命名为PLA2－I（SWISS－PROT,P82892）、Ⅱ（SWISS-PROT,P82893）、Ⅲ（SWISS－PROT,P82894）、Ⅳ（SWISS－PROT,P82895）、V（SWISS－PROT,P82896）。SDS－PAGE测定它们的分子量分别为14．0、15．8、15．0、14．0和14．0kDa。等电聚焦电泳测得PLA2－I、Ⅱ、Ⅲ呈碱性,等电点大于8．8;PLA2－Ⅳ和V呈酸性,等电点分别为5．2和4．7。PLA2－Ⅳ和V有水解卵磷脂活性。用自动Edman降解法测定了PLA2－V的全部氨基酸序列和PLA2－I、Ⅱ、Ⅲ、Ⅳ的N－端部分氨基酸序列。PLA2－V由122个氨基酸残基组成,有14个Cys,并与其它来源的PLA2的氨基酸序列进行了比较。     

白蛇传:从蛇图腾到具有反叛力的女性话语

从白蛇传传说的历史渊源和发展演变来看，白蛇传传说与我国古代民族蛇文化的崇拜密切相关。另一方面，白娘子其一言一行均颠覆和瓦解着封建的“男女授受不亲”观念，形象地为人间女性争夺了数千年来难以取得的社会平等地位。《白蛇传》张扬的是女性的自身权益，凸现的是具有反叛力量的女性话语。     

Unusually large earthquakes inferred from tsunami deposits along the Kuril trench

The Pacific plate converges with northeastern Eurasia at a rate of 8-9 m per century along the Kamchatka, Kuril and Japan trenches. Along the southern Kuril trench, which faces the Japanese island of Hokkaido, this fast subduction has recurrently generated earthquakes with magnitudes of up to approximately 8 over the past two centuries. These historical events, on rupture segments 100-200 km long, have been considered characteristic of Hokkaido's plate-boundary earthquakes. But here we use deposits of prehistoric tsunamis to infer the infrequent occurrence of larger earthquakes generated from longer ruptures. Many of these tsunami deposits form sheets of sand that extend kilometres inland from the deposits of historical tsunamis. Stratigraphic series of extensive sand sheets, intercalated with dated volcanic-ash layers, show that such unusually large tsunamis occurred about every 500 years on average over the past 2,000-7,000 years, most recently approximately 350 years ago. Numerical simulations of these tsunamis are best explained by earthquakes that individually rupture multiple segments along the southern Kuril trench. We infer that such multi-segment earthquakes persistently recur among a larger number of single-segment events.     

精制蛇毒乳膏治疗痤疮的疗效观察

选用中国医科大学老年病防治中心研制的精制蛇毒乳膏治疗100例额面痤疮患者。痊愈率65 % ,有效率99 % ,疗效满意     

颅骨弹性模量时效性的实验研究

采用猪颅骨为实验材料,使用应变电测法对颅骨各层弹性模量随风干时间的变化规律进行了实验研究.实验结果表明:密质骨弹性模量约是松质骨弹性模量的2.5倍,松质骨对颅骨弹性模量的影响有限;猪颅骨单层密质骨和整体的弹性模量相差约13.9%;冷冻后经室温下自然解冻的猪颅骨单层密质骨的弹性模量变化量相当于新鲜密质骨的9.2%,单纯板障松质骨片的变化量为17%,去掉一层密质骨后的颅骨片变化量为18.1%,整体猪颅骨片的变化量为15.6%;由于各生物体颅骨结构基本相同.由此可知,如果在人颅骨上也能得到相似的结论,在进行有关人颅骨研究时可大大延长同一块颅骨的使用时间.或者可以用风干颅骨、解冻后风干颅骨来代替新鲜骨,然后根据其时效特性对实验数据进行修正,这样会大大降低实验成本和难度.