本文選題：早寒武世 + 西鄉(xiāng)生物群��； 參考：《長(zhǎng)安大學(xué)》2017年碩士論文

【摘要】：寒武紀(jì)特異埋藏化石生物群在探索早期生命起源與演化方面有特別重要的意義。西鄉(xiāng)生物群賦存于陜南西鄉(xiāng)境內(nèi)寒武系底部含磷巖系中,是一個(gè)特異保存的微骨骼化石群�；M合面貌可與早寒武世梅樹村階微骨骼化石對(duì)比,時(shí)代歸屬早寒武世梅樹村期。含有數(shù)量龐大、種類豐富、且保存完好的各門類化石,所發(fā)現(xiàn)的許多珍貴化石材料豐富了寒武紀(jì)生命大爆發(fā)的內(nèi)容,是早期生命演化與起源研究的精彩窗口。本文通過(guò)野外踏勘、樣品采集、和大量的標(biāo)本處理,對(duì)西鄉(xiāng)生物群中的軟舌螺、似軟舌螺、阿納巴管、環(huán)神經(jīng)動(dòng)物、四方塔形殼和棘盔類這六個(gè)主要化石類型進(jìn)行了重點(diǎn)研究,對(duì)這幾類化石的研究現(xiàn)狀、西鄉(xiāng)生物群中出現(xiàn)的化石種屬及其重點(diǎn)特征等進(jìn)行了總結(jié)歸納,主要成果有:1.軟舌螺化石及內(nèi)部結(jié)構(gòu)研究經(jīng)過(guò)初步研究統(tǒng)計(jì),西鄉(xiāng)生物群中的軟舌螺數(shù)量龐大,可占生物群化石總量的60%~70%,且均屬直管螺綱、圓管螺目,主要為Circotheca Sysoiev,1958,也有少量的Pseudovalitheca Qian,1989,認(rèn)為其屬于中國(guó)寒武紀(jì)軟舌螺演化的第一階段。同時(shí)通過(guò)對(duì)大量巖石薄片進(jìn)行統(tǒng)計(jì),重點(diǎn)研究了軟舌螺化石的多種內(nèi)部結(jié)構(gòu),將軟舌螺的內(nèi)部結(jié)構(gòu)劃分成幾大類,總結(jié)認(rèn)為其中單層殼以及多層殼的同心管狀軟舌螺殼體為原生結(jié)構(gòu),占總數(shù)的70%;而多層殼的偏心管則為水流搬運(yùn)所致的次生結(jié)構(gòu),占總數(shù)的30%。推測(cè)多層殼壁結(jié)構(gòu)可加固管體,是地球早期生物為應(yīng)對(duì)同期出現(xiàn)的食肉動(dòng)物所進(jìn)化出的生存對(duì)策。2.阿納巴管及其對(duì)稱性演化研究西鄉(xiāng)生物群中的阿納巴管主要為Anabarites trisulcatus Missarzhevsky,1969,Aculeochrea tripartitus Missarzhevsky,1969與Anabarites isiticus Missarzhevsky,1974三屬,其中A.isiticus化石殼體表面的生長(zhǎng)紋可明顯分為較粗與較細(xì)兩類,體現(xiàn)了生物不同的生長(zhǎng)周期。同時(shí)在西鄉(xiāng)生物群產(chǎn)出的大量三輻射對(duì)稱阿納巴管中,一些特殊的A.trisulcatus化石呈現(xiàn)出了從三輻射對(duì)稱演化后期階段到六輻射對(duì)稱演化階段之間的過(guò)渡,與三輻射對(duì)稱演化后期階段、六輻射對(duì)稱演化階段(以Anabarites sexalox為代表)形成一個(gè)演化序列,顯示出在由三射向六射演化的過(guò)程中,新的三條二級(jí)縱槽并不是同時(shí)形成,而是逐漸依序形成。由于生物對(duì)稱性在進(jìn)化上所具有的保守性,據(jù)此推測(cè),在生物由六輻射對(duì)稱向十二輻射對(duì)稱、進(jìn)而向二十四輻射對(duì)稱等更多倍數(shù)輻射對(duì)稱的演化過(guò)程中,也應(yīng)遵循這個(gè)規(guī)律,是每二增加一條二級(jí)的縱槽,從而逐漸依序進(jìn)行演化。3.Quadrapyrgites胚胎化石新發(fā)現(xiàn)及其對(duì)個(gè)體發(fā)育序列的完善前人對(duì)四方塔形殼的形態(tài)特征、內(nèi)部結(jié)構(gòu)及生長(zhǎng)模式等研究已經(jīng)較為深入,并初步建立起了其個(gè)體發(fā)育序列,然而一些重要的生長(zhǎng)階段,主要是幼體期之前的卵裂期胚胎、四分卵裂期及預(yù)孵化期的完整化石由于階段存在時(shí)間短、難以保存,仍很缺乏,最近在西鄉(xiāng)生物群中發(fā)現(xiàn)了一枚新的四方塔形殼胚胎化石標(biāo)本,應(yīng)處于預(yù)孵化晚期�；瘶�(biāo)本表面光滑無(wú)飾,已有四方塔形殼的原型,化石口部雛形初現(xiàn)、底部的四方錐狀體也已明顯分化。此胚胎化石保存完好,特征清晰,且處于重要的個(gè)體發(fā)育階段,將為四方塔形殼個(gè)體發(fā)育序列增加重要的新材料。同時(shí),將此胚胎化石與其姊妹類群punctatus中的兩種進(jìn)行了比較,此化石由于其光滑而無(wú)星狀棘突、強(qiáng)烈褶皺或縱紋的外表,12個(gè)花瓣的口部和四輻射對(duì)稱的典型錐體而與punctatus相區(qū)別。
[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.
【學(xué)位授予單位】：長(zhǎng)安大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：Q915

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