【摘 要】
：
We present the first parsimony analysis of the agnathan subclass Galeaspida based on the analysis of 53 morphological characters.Three most parsimonious cladogr
【机 构】
：
Institute of Vertebrate Paleontology and Paleoanthropology,Chinese Academy of Sciences,Beijing 10004
论文部分内容阅读
We present the first parsimony analysis of the agnathan subclass Galeaspida based on the analysis of 53 morphological characters.Three most parsimonious cladograms (126 steps in length;CI=0.508;RI=0.801)were discovered.An amended classification of the Galeaspida is proposed corresponding to the present analysis.Our results suggest that hanyangaspids,xiushuiaspids and dayongaspids from the Llandovery-Wenlock of Silurian are basal galeaspids.Within the remaining galeaspids,three major monophyletic groups (the Eugaleaspidiformes,the Polybranchiaspidiformes and the Huananaspidiformes)are well supported.It is shown that the dorsal fenestrae of the headshield evolved twice within the Galeaspida,one in the polybranchiaspidiform lineage,and the other in the huananaspidiform lineage (nested within the Huananaspidae).The chronological distribution of galeaspids highlights two radiations of the group,one for basal galeaspids and eugaleaspids in the Telychian (Llandovery)of Silurian,and the other for polybranchiaspidiforms and huananaspidiforms in the Lochkovian of Early Devonian.
其他文献
把握水下溢油时油滴粒径的分布规律是研究溢油行为和归宿的前提,也是水下溢油事故有效应急处置的重要依据。本研究采用自制的1 m×1 m×2 m(长×宽×高)的水下溢油模拟实验装
广西是我国的主要甘蔗产区，总产量约占全国60%以上，但甘蔗生产施用氮肥量过高，生产成本高。因此合理施肥，提高氮肥利用率，降低甘蔗生产成本是当前广西甘蔗生产的重要任务。接种联
Traditional agroecosystems play an important role in the conservation of biodiversity and in sustainable development.As a typical type of traditional agroecosys
Both thymocytes and tumor cells express M2 type isoenzyme of pyruvate kinase (M2PK), which is different from R type isoenzyme of pyruvate kinase (RPK) that is e
Vibrio harveyi,the major causative agent of vibriosis,affects a diverse range of marine cultured organisms over a wide geographical area.However,reports about s
面粉白度是衡量小麦品质的重要性状之一，受遗传和环境影响。其中，多酚氧化酶（polyphenol oxidase，PPO）是引起面条(团)颜色褐变的主要原因。研究表明降低籽粒PPO活性可以改良小麦面粉白度，因此可以通过基因转化、RNAi等基因工程方法来降低内源PPO基因的表达，抑制PPO的活性，增加面粉白度等。本研究首先进行了小麦成熟胚再生体系的优化和优良基因型的筛选，其次利用ppo基因构建了植物R
Endosomal compartments sort and deliver exogenous lipoprotein-derived cholesterol to the endoplasmic reticulum for regulating cellular cholesterol homeostasis.
MicroRNAs (miRNAs) and small interfering RNAs (siRNAs) regulate gene expression in eukaryotes.Plant miRNAs modulate their targets mainly via messen-ger RNA (mRN
本文采用2003～2016年SSMI海冰密集度和NCEP气温、风场等数据,通过计算海冰覆盖率、增长期长度、冬季负积温和风拖曳力等参数,分析了巴伦支海海冰的变化特征及其与热力、动力影
Some novel members of extremely halophilic archaea, strains AJ 11, AJ 12 and AJ 13, were isolated from the Aularz Lake located in the Altun Mountain National Na