Extinctions, Morphological Gaps, Major Transitions, Stem Groups, and the Origin of Major Clades, with a Focus on Early Animals     

XIAO Shuhai 《《地质学报》英文版》2022,96(6):1821-1829

Systematic extinctions can leave major morphological gaps between living crown-group clades. Such morphological gaps would be perceived, from a neontological point of view, as major evolutionary transitions. In order to fill these morphological gaps and to map the evolutionary steps toward major evolutionary transitions, we need to integrate extinct stem-group taxa in phylogenetic studies. However, the recognition of stem group has not been widely adopted in the study of early animal fossils, despite that all fossils are stem groups at one level or another. Part of the difficulty is that stem groups may not have all features that collectively diagnose the respective crown group, and they can have unique (autapomorphic) features, making them tantalizingly similar to and frustratingly different from the crown group (e.g., stem-group eukaryotes can be prokaryotic and stem-group animals can be protistan). The need to embrace stem groups and to implement the PhyloCode, in order to achieve phylogenetic clarity and to offer key paleontological insights into the origin and early animal evolution, is illustrated in debates on several controversial Ediacaran and Cambrian fossils.  相似文献   

Haitaite-(La), LaU4+Fe3+2(Ti13Fe2+4Fe3+)Σ18O38, a New Member of the Crichtonite Group     

WANG Fenggang  FAN Guang  LI Ting  GE Xiangkun  WU Yu  WANG Tao  YAO Jian 《《地质学报》英文版》2022,96(6):2007-2014

Haitaite-(La), (La, Ce)(U4+, U6+, Fe2+)(Fe3+, Al)2(Ti, Fe2+, Fe3+)18O38, is a new member of the crichtonite group. It is named after the Haita Village in the Miyi County of Sichuan Province, China, where the mineral was discovered. The mineral occurs as black opaque centimeter-sized aggregates in the external contact zone between the Neoproterozoic (~800 Ma) alkali feldspar granite and the Mesoproterozoic (~1700 Ma) micaschist. In the studied sample, haitaite-(La) is associated with other minerals, including ilmenite, magnetite, rutile, zircon, brannerite and uraninite. The new mineral is a black, metallic phase and has a Mohs hardness of 6, with a density of 4.99 g/cm3 (calculated) and 5.03 g/cm3 (measured). Haitaite-(La) is opaque in transmitted light and grayish-white under reflected light, with a reflectivity between 22.5% and 16.42% in the 400–700 nm band (SiC, in the air). The compositions of the mineral were measured by EPMA, the U4+/U6+ ratio was determined by X-ray photoelectron spectroscopy and the Fe2+/Fe3+ ratio was determined by M?ssbauer spectroscopy. Haitaite-(La) is trigonal, belongs to R3ˉ and has unit-cell parameters a = 10.3678(5) ?, c = 20.8390(11) ?, V = 1939.9(2) ?3, Z = 3. The crystalline structure is composed of octahedra with 9 layers of close-packed octahedra (M1, M3, M4, M5), tetrahedra (M2) and contains large 12-coordinated M0 sites.  相似文献   

The Statherian itabirite-bearing sequence from the Morro Escuro Ridge,Santa Maria de Itabira,Minas Gerais,Brazil     

《Journal of South American Earth Sciences》2015

The itabirite-bearing metasedimentary sequence from Morro Escuro Ridge comprises the basal units of the Espinhaço Supergroup and makes up a small tectonic inlier developed during one of the Brasiliano orogenic events (800-500 Ma), amongst horses of the Archean TTG gneisses, including sheared granites of the anorogenic Borrachudos Suite (∼1700 Ma). The metasedimentary rocks are comprised of low-to intermediate-amphibolite facies schists, quartzites, conglomerates and banded iron formation (itabirite) correlatable with the sequences of the Serro Group, which underlies the metasedimentary rocks of the Espinhaço Supergroup in the Serra da Serpentina Ridge. A maximum Statherian deposition age (1668 Ma) was established using SHRIMP U–Pb isotopic constraints on zircon grains from conglomerate and quartzite units overlying the itabirite. The itabirite is predominantly hematitic and its geochemical characteristics are typical of a Lake Superior-type BIF deposited in a platformal, suboxic to anoxic environment distant from Fe-bearing hydrothermal vents. Close to the contact zone with amphibolites of the Early Neoproterozoic Pedro Lessa mafic suite, an increase of the magnetite content and crystallization of metasomatic Mg-hornblende and Ce-allanite can be observed. These mineralogical changes developed preferentially along the igneous contact zone but are probably co-genetic with the formation of alteration haloes in zircon grains during the Neoproterozoic Brasiliano orogeny (506 ± 6 Ma).  相似文献   

角闪石族和辉石族矿物的系统矿物学分类命名   总被引：1，自引：0，他引：1  

刘显凡  汪灵  李慧  刘菁  赵甫峰  卢秋霞  胡琳 《矿物学报》2015,35(1):19-28

角闪石族和辉石族矿物是链状硅酸盐矿物的重要组成部分,它们中的许多矿物种属于造岩矿物和/或工业矿物,具有重要的成因矿物研究意义和工业应用开发价值。国内学者对它们的分类命名和基本系统认识主要源自于王璞等(1984)编著的《系统矿物学》。随着科学技术发展和矿物学研究的不断深入,原有的矿物基础资料和分类命名都在不断更新与完善,迄今已有专业学术机构和学者在不同年代陆续发表了不同版本对该两类矿物的修订或修改意见,但一直没有统一整合,导致在涉及该两类矿物的应用研究中,在分类命名上与国际标准不统一。根据本课题组在国家公益性行业科研专项项目(新编《系统矿物学》)所承担的研究任务和当前国内外研究进展,本文系统归纳、梳理并综述了角闪石族和辉石族矿物的分类方案和命名原则,使分类命名统一标准、原则和认识并与国际接轨,这有利于该两类矿物的理论研究与开发应用,更好地支撑地质学及相关学科的研究与发展。  相似文献   

基于灰区间真值的群体决策方法及应用     

巩在武  郭崇兰  周显信 《南京气象学院学报》2013,5(2):171-177

研究了灰区间偏好的群体决策问题.在专家灰区间偏好群体意见集结过程中,常规的灰区间运算会产生决策信息的失真.为了避免这一缺陷,首先引入了灰区间调节参数的概念,通过建立求解调节参数的二次规划模型,确定专家灰区间判断的真值.建立了专家客观权重求解的二次规划模型,并给出了专家客观权重的最优解.此外,从另外一个角度同时考虑调节参数与客观权重,建立求解灰区间真值与专家客观权重的群体最优决策模型.气象敏感性行业专家群体评估决策的算例表明,决策策略是有效的.  相似文献   

Masses of the local group and of the M81 group estimated from distortions in the local velocity field     

I. D. Karachentsev  O. G. Kashibadze 《Astrophysics》2006,49(1):3-18

Based on high precision measurements of the distances to nearby galaxies with the Hubble telescope, we have determined the radii of the zero velocity spheres for the local group, R₀ = 0.96±0.03Mpc, and for the group of galaxies around M 81/M 82, 0.89±0.05Mpc. These yield estimates of M_T = (1.29±0.14)· 10¹² M_⊙ and (1.03±0.17)· 10¹² M_⊙, respectively, for the total masses of these groups. The R₀ method allows us to determine the mass ratios for the two brightest members in both groups, as well. By varying the position of the center of mass between the two principal members of a group to obtain minimal scatter in the galaxies on a Hubble diagram, we find mass ratios of 0.8:1.0 for our galaxy and Andromeda and 0.54:1.00 for the M82 and M81 galaxies, in good agreement with the observed ratios of the luminosities of these galaxies. __________ Translated from Astrofizika, Vol. 49, No. 1, pp. 5–22 (February 2006).  相似文献   

领导团体腐败和作弊的社会经济影响：数量特征与客观评价     

牛福增  阎怀艳 《广东海洋大学学报》2005,25(5):40-45

20世纪90年代以来,我国因领导团体作弊型腐败造成的经济和消费者福利损失迅速增加,其根本原因是行政权力对经济与市场的管制和干预,租金的来源主要是由政府控制引起的“公共区域”。学者们对我国租金价值计算表明,我国租金的绝对量有扩大的趋势,租金结构也发生了相应的变化。随着国家对经济活动管制的减少,租金的比例有降低的趋势。领导团体作弊型腐败不但扭曲了政府决策的合理性,并产生了严重的负外部性,且可能导致政府管理的失败,降低资源配置的效率和阻滞了国家的经济增长,最终影响到社会的稳定。官员腐败和作弊产生于制度的漏洞或不完善。制约与解决的有效手段是寻找能够适应生产力发展要求的新的制度安排。  相似文献   

贺兰山群早元古代花岗岩的地质特征和岩石谱系单位划分     

李伍平 《地球科学与环境学报》1994,(3)

通过对呼鲁斯太幅和古拉本幅的１／５万区域地质调查工作，对该地区太古代贺兰山群中－高级变质岩中早元古代花岗岩进行了岩石谱系单位的划分和填图。在此基础上，从花岗岩的地质学、岩石学、岩石化学和地球化学等方面进行了较系统的详细研究，把早元古代花岗岩划分出７个单元，并将其中的５个单元归并为两个超单元。  相似文献   

论丽水运动     

马武平 《浙江国土资源》1997,(1)

本文以翔实的地质资料，就丽水以南吴弄口盆地的永康群与丽水南明山一带丽水盆地的天台群之间呈角度不整合接触关系，及其地层层序作了全面论述，认为它们之间存在一次重要意义的地壳运动──丽水运动。  相似文献   

基于JXTA的协同学习系统研究     

胡皓  杨雪  刘波 《成都信息工程学院学报》2007,22(4):479-481

随着计算机网络技术的迅速发展和计算机协同工作CSCW理论和技术研究的深入,计算机协同学习(Computer Supported Collaborative Learning)的思想逐渐被引入计算机网络教育的应用中.目前大多数的协同学习系统采用了C/S结构.提出的基于JXTA的协同学习系统采用了P2P(Peer-to-Peer)结构,满足了协同学习的一般需求,具有安全性、可伸缩性和可扩展性.  相似文献