西乡生物群磷酸盐化特异埋藏化石研究

发布时间：2018-07-10 12:00

本文选题：早寒武世 + 西乡生物群　；参考：《长安大学》2017年硕士论文

【摘要】：寒武纪特异埋藏化石生物群在探索早期生命起源与演化方面有特别重要的意义。西乡生物群赋存于陕南西乡境内寒武系底部含磷岩系中,是一个特异保存的微骨骼化石群。化石组合面貌可与早寒武世梅树村阶微骨骼化石对比,时代归属早寒武世梅树村期。含有数量庞大、种类丰富、且保存完好的各门类化石,所发现的许多珍贵化石材料丰富了寒武纪生命大爆发的内容,是早期生命演化与起源研究的精彩窗口。本文通过野外踏勘、样品采集、和大量的标本处理,对西乡生物群中的软舌螺、似软舌螺、阿纳巴管、环神经动物、四方塔形壳和棘盔类这六个主要化石类型进行了重点研究,对这几类化石的研究现状、西乡生物群中出现的化石种属及其重点特征等进行了总结归纳,主要成果有:1.软舌螺化石及内部结构研究经过初步研究统计,西乡生物群中的软舌螺数量庞大,可占生物群化石总量的60%~70%,且均属直管螺纲、圆管螺目,主要为Circotheca Sysoiev,1958,也有少量的Pseudovalitheca Qian,1989,认为其属于中国寒武纪软舌螺演化的第一阶段。同时通过对大量岩石薄片进行统计,重点研究了软舌螺化石的多种内部结构,将软舌螺的内部结构划分成几大类,总结认为其中单层壳以及多层壳的同心管状软舌螺壳体为原生结构,占总数的70%;而多层壳的偏心管则为水流搬运所致的次生结构,占总数的30%。推测多层壳壁结构可加固管体,是地球早期生物为应对同期出现的食肉动物所进化出的生存对策。2.阿纳巴管及其对称性演化研究西乡生物群中的阿纳巴管主要为Anabarites trisulcatus Missarzhevsky,1969,Aculeochrea tripartitus Missarzhevsky,1969与Anabarites isiticus Missarzhevsky,1974三属,其中A.isiticus化石壳体表面的生长纹可明显分为较粗与较细两类,体现了生物不同的生长周期。同时在西乡生物群产出的大量三辐射对称阿纳巴管中,一些特殊的A.trisulcatus化石呈现出了从三辐射对称演化后期阶段到六辐射对称演化阶段之间的过渡,与三辐射对称演化后期阶段、六辐射对称演化阶段(以Anabarites sexalox为代表)形成一个演化序列,显示出在由三射向六射演化的过程中,新的三条二级纵槽并不是同时形成,而是逐渐依序形成。由于生物对称性在进化上所具有的保守性,据此推测,在生物由六辐射对称向十二辐射对称、进而向二十四辐射对称等更多倍数辐射对称的演化过程中,也应遵循这个规律,是每二增加一条二级的纵槽,从而逐渐依序进行演化。3.Quadrapyrgites胚胎化石新发现及其对个体发育序列的完善前人对四方塔形壳的形态特征、内部结构及生长模式等研究已经较为深入,并初步建立起了其个体发育序列,然而一些重要的生长阶段,主要是幼体期之前的卵裂期胚胎、四分卵裂期及预孵化期的完整化石由于阶段存在时间短、难以保存,仍很缺乏,最近在西乡生物群中发现了一枚新的四方塔形壳胚胎化石标本,应处于预孵化晚期。化石标本表面光滑无饰,已有四方塔形壳的原型,化石口部雏形初现、底部的四方锥状体也已明显分化。此胚胎化石保存完好,特征清晰,且处于重要的个体发育阶段,将为四方塔形壳个体发育序列增加重要的新材料。同时,将此胚胎化石与其姊妹类群punctatus中的两种进行了比较,此化石由于其光滑而无星状棘突、强烈褶皱或纵纹的外表,12个花瓣的口部和四辐射对称的典型锥体而与punctatus相区别。
[Abstract]:The Cambrian specific buried fossils are of special significance in exploring the origin and evolution of early life. The Xixiang biota exists in the fossilized rock series at the base of the Cambrian in Xixiang, southern Shaanxi. It is a specific preserved fossilized fossil group. The fossil assemblage can be compared with the Early Cambrian Mei tree village level fossils. It belongs to the period of the Early Cambrian Mei tree village. It contains a large number, rich species and well preserved fossils. Many precious fossil materials have been found to enrich the content of the Cambrian life eruption. It is a wonderful window for the study of early life evolution and origin. This article through the field exploration, sample collection, and a large number of specimen processing, to Xixiang The six main types of fossils in the biota, such as pic, arinba, annulas, tetragonal and spinous helmets, are mainly studied. The research status of these fossils, the fossil species belonging to the Xixiang biota and their key features are summarized, and the main achievements are: 1. According to the preliminary study, the number of snail in the Xixiang biota is large, and it can account for 60%~70% of the total biomass of the biota, and all belong to the class of straight tube snails and round snails, mainly Circotheca Sysoiev, 1958, and a small amount of Pseudovalitheca Qian, 1989, which belong to the first stage of the evolution of Cambrian snail in China. Through the statistics of a large number of rock slices, the internal structure of the conch fossils is mainly studied, and the internal structure of the conch is divided into several categories. It is concluded that the concentric tubular soft tongue shell body of the single layer shell and the multilayer shell is the primary structure, accounting for 70% of the total, while the eccentric tube of the multi-layer shell is secondary to the flow of the flow. The structure, which accounts for the total number of 30%., speculates that the multi-layer shell structure can reinforce the pipe body. It is the survival strategy of the early life of the earth to respond to the carnivorous animals of the same period,.2. ARBA tube and its symmetry evolution study in the Xixiang biota, the ARBA tube is mainly Anabarites trisulcatus Missarzhevsky, 1969, Aculeochrea tripartitus Mi. Ssarzhevsky, 1969 and Anabarites isiticus Missarzhevsky, 1974 three genera, among which the growth patterns of the surface of the A.isiticus fossils can be clearly divided into coarser and thinner two types, reflecting the different growth cycles of the organisms. At the same time, some special A.trisulcatus fossils are presented in a large number of three radially symmetric ARBA tubes produced by the Xixiang biota. The transition from the later stage of the three radiation symmetry evolution to the six radiation symmetry evolution stage, and the later stage of the three radiation symmetry evolution, and the six radiation symmetry evolution phase (represented by Anabarites sexalox) form an evolutionary sequence, showing that the new three two longitudinal grooves are not conconcurrently in the course of the evolution from three to six. As a result of the conservatism of biological symmetry in evolution, it is presumed that in the process of biological evolution from six symmetry to twelve radiation symmetry, and then to twenty-four radiation symmetry and so on, it is also necessary to follow this rule, an increase of a two level slot per two. The new discovery of evolutionary.3.Quadrapyrgites embryo fossils and the improvement of the individual development sequence have been carried out by previous studies on the morphological characteristics, internal structure and growth patterns of the tetragonal pyramidal shells, and initially established their individual development sequences. However, some important stages of growth are mainly the cleavage period before the juvenile stage. The complete fossils of the four split and pre hatching stages are short, difficult to preserve and still lack. Recently, a new tetragonal tower shaped shell embryo is found in the Xixiang biota, which should be in the late stage of pre incubation. The surface of the fossils is smooth and undecorated. The fossils of this embryo are well preserved, clearly characterized, and at an important stage of individual development, which will add important new materials to the sequence of the tetragonal tower hull individual development. At the same time, the fossils of this embryo are compared with two of their sister group punctatus, the fossils because of their smoothness and no stars. Spines, strongly wrinkled or longitudinally striped, 12 petals' mouth and four radially symmetric pyramids, which are distinguished from punctatus.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：Q915

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