华南寒武纪鳃曳动物形态分类与谱系演化研究

发布时间：2018-07-13 19:10

【摘要】：鳃曳动物是原口动物亚界蜕皮类群中的一个小门,现生类型迄今只描述了7属19种。然而,软躯体鳃曳动物却是寒武纪海洋中底内生物群落的优势类群,具有非常高的形态差异度和个体丰度。华南寒武纪台地相和斜坡相一系列特异埋藏化石群保存有大量鳃曳动物化石,是研究鳃曳动物早期起源与辐射、蜕皮动物起源与演化以及“寒武纪大爆发”等基础前沿课题的重要化石材料。但是,目前学术界对早期鳃曳动物的系统分类、辐射演化、古生态学特征和系统演化关系等问题仍有较大争议。在系统总结前人研究成果基础上,本文对湖北三峡地区的石牌生物群(台地相,寒武系第4阶)、陕西西乡三郎铺地区的西乡生物群(台地相,寒武系第4阶)、贵州剑河革东地区的剑河生物群(斜坡相,寒武系第4阶晚期)和凯里生物群(斜坡相,寒武系第5阶早期)等化石群中的鳃曳动物化石材料进行研究,力求对上述学术界长期争议的科学问题有所解答。本文系统描述了四个生物群中的古蠕虫类化石5属8种,包括3个新属新种、2个新种和2个未定种。其中,Sanxiascolex papillogyrus gen. et sp. nov., Wronascolex yichangensis sp. nov.和W. spinosus (Ivanstsov and Wrona,2004)描述于石牌生物群；Shaanxiscolex xixiangensis gen. et sp. nov.为西乡生物群的特有类型：Guizhouscolex balangensis gen. et sp. nov.和Yunnanscolex sp.是剑河生物群的两个新类型；W. jianhensis sp. nov.和W.sp.则是凯里生物群的化石分子。此外,Gen. et sp. uncertain A和Gen. et sp. uncertain B是两个分别描述于剑河生物群和凯里生物群的未正式命名新类型。这些化石属种都具有常见于早古生代地层的Hadimopanella类骨板,但不同类型之间骨板系(scleritomes)特征均显示出一定差异性,这与地史时期不同产地和层位古蠕虫类的骨板特征多不相同的情形相一致,说明古蠕虫类的表皮骨板构造可能与海底沉积物的性质有关。论文系统讨论了Wronascolex属的分类原则、古地理分布和地史延限,结果表明该属是寒武纪分异度最高(含8种和3未定种)、分布范围最广(华南、西伯利亚、澳大利亚、西班牙和北美)、延限时间最长(寒武系第4阶至鼓山阶)的古蠕虫类实体化石。但是,Wronascolex的属征仍不明确,而且Hadimopanella孤立骨板的形态分类研究争议较大,大大削弱了该化石属及其骨板的地层学意义。另外,石牌生物群中W. spinosus的骨板具有独特的排列方式,表明古蠕虫类的骨板可能具有多种增长模式。本文还研究了云南澄江动物群中的古蠕虫类Mafangscolex yunnanensis (Luo et Zhang),1986,首次识别出该种躯干腹侧有圆锥状感觉构造和可能的腿肢,为古蠕虫类形态学、古生态学和系统演化研究提供了新信息。化石证据显示,古蠕虫类具有较强的掘穴能力,部分类型可能兼有潜穴和底表爬行生活方式,并偶尔食含腐质沉积物。尽管古蠕虫类部分孤立骨板类型(如Hadimopanella)的最早化石记录可追溯到寒武系第二阶晚期,但处于第三阶的澄江动物群代表鳃曳动物的首次辐射演化事件。寒武纪时期不同化石群中鳃曳动物的组合面貌差异很大,多数类型为各个生物群的特有分子,只有少数属种具有较长的地史延限,说明早期鳃曳动物在不同生活环境下有较好的适应能力并发生快速分异演化。寒武纪早期扬子台地斜坡相至台地相地层都有大量鳃曳动物化石产出,表明华南滇东浅海地区未必是这一时期鳃曳动物的辐射中心。凯里生物群产有重要鳃曳动物类型Ottoia和Sicyophorus。研究结果显示,凯里生物群的奥托虫体长50-80 mm,外伸的翻吻有25列纵列吻刺,后部短柱形；躯干宽度较均匀,具密集环纹,达13条/5mm；咽部和肠道之间有一个可能的肌胃；肠道壁见肌纤维；躯干后部有1对长的后伸缩肌。这些特征明显不同于布尔吉斯页岩生物群(Burgess Shale)中的O. prolifica Walcott,1911,命名为贵州奥托虫O. guizhouensis Yang, Zhao et Zhang,2015。原地埋藏的O. guizhouensis保存有虫体正在钻泥掘穴的证据,而且肠道有泥质充填物,表明Ottoia是一种能在底表沉积物中多维度自由穿梭、偶尔食泥质生活的底内动物,并非此前推测那样穴居于U型管穴中。通过类比澄江动物群中的特殊鳃曳动物类型Sicyophorus rara Luo et al.,1999和Palaeopriapulites parvus Hou et al.,1999,识别出凯里生物群中葫芦虫的躯干大约有50条纵列隔板,颈部有2-3条环纹,末端有一条较短的尾突构造,因而建立贵州葫芦虫(新种)S. guizhouensis sp. nov.。形态学和解剖学证据表明,Sicyophorus既有相似于鳃曳动物的形态构造(翻吻和尾突),也有类似于铠甲动物的躯干特征(具纵列隔板),而卷曲盘绕的肠道区别于其他环神经类动物,可能是鳃曳动物向铠甲动物演化过程中幼态持续发育而来的一个特化类型。本文运用TNT软件对O. guizhouensis和S. guizhouensis的系统演化位置进行分析。谱系分支树显示,Ottoia属于Scalidophora干群类型,而Sicyophorus位于Scalidophora冠群底部靠近铠甲动物的位置,支持由鳃曳动物幼态持续发育而来的观点。此外,古蠕虫类不同属种的系统演化位置差别很大。根据形态学、解剖学证据和谱系分析,论文讨论了两侧对称动物祖先类型Urbilateria-叶足动物Xenusia- Scalidophora干群类型Fieldiai和Ancalagonia—古蠕虫类Palaeoscolecida—Louisellia—鳃曳动物Priapulida—葫芦虫Sicyophourus—铠甲动物Loricifera整个演化线系中各个节点动物代表的身体构型特征,认为部分古蠕虫类(如M.yunnanensis)可能具有相似于蜕皮动物祖先类型的形态特征。
[Abstract]:Branchial tracer is a small door in the subboundary molt group of the original animal, and the present type has only described 7 genera and 19 species so far. However, the soft somatic branchial tracer is the dominant group in the Cambrian middle subsea biological community, with very high morphological difference and individual abundance. A series of special burial of the Cambrian platform and slope facies in Southern China. The stone group has a large number of branchial fossils. It is an important fossil material for the study of the early origin and radiation of the branchial tracers, the origin and evolution of molt, and the "Cambrian outbreak". However, the systematic classification, radiological evolution, paleo ecological characteristics and systematic evolution of the early branchial tracers in the academic circles are at present. On the basis of a systematic summary of the achievements of previous studies, this paper is based on the stone brand biota in the Three Gorges area (terracostage, Cambrian fourth), Xixiang biota (terrace, Cambrian, fourth) in the Sanlun area, Xixiang, Xixiang, and the Jianhe biota (slope facies, late Cambrian in the late fourth order) and Kay in Jianhe, Guizhou. The study of the branchial fossil materials in the fossils of the fossils of the biota (slope facies and the Early Cambrian fifth order) has been studied in order to solve the scientific problem of the long term controversy in the academic circles. This paper systematically describes the 5 genera and 8 species of the paleo worms of the four biota, including 3 new species, 2 new species and 2 undetermined species. Among them, Sanxiasc Olex papillogyrus Gen. et sp. Nov., Wronascolex yichangensis sp. Nov. and W. spinosus, described in the Xixiang biota of biota. The two new types, W. jianhensis sp. Nov. and W.sp. are the fossil molecules of the Kaili biota. In addition, Gen. et sp. uncertain A and Gen. et are two unofficially named new types described respectively in the biota and the Kaili biota. These species are all common in the early Paleozoic strata. Bone plate, but the characteristics of different types of bone plate system (scleritomes) show a certain difference, which is consistent with the different characteristics of the bone plate characteristics of different habitats and layers of ancient worms in the period of geological history, indicating that the structure of the epidermal bone plate of the ancient worms may be related to the nature of the seabed sediments. This paper systematically discusses the Wronascolex genus. The classification principle, palaeogeographic distribution and earth history extension limit indicate that the genus is the highest (8 species and 3 undetermined species) in Cambrian (including 8 species and 3 undetermined species), and the most widely distributed (Southern China, Siberia, Australia, Spain and North America) and the oldest (Cambrian, fourth to GUSHAN) paleogeic solid fossils. However, the genera of Wronascolex are still not clear. Moreover, the study of the morphological classification of the Hadimopanella isolated bone plates has greatly weakened the Stratigraphic Significance of the fossil genus and its bone plate. In addition, the bone plate of the W. spinosus in the stone brand biota has a unique arrangement, indicating that the bone plates of the ancient worms may have a variety of growth patterns. This paper also studied the Chengjiang fauna of Yunnan. The ancient worms Mafangscolex yunnanensis (Luo et Zhang), 1986, identified the conical structure and possible leg limbs on the ventral side of the trunk for the first time. It provides new information for the study of the morphological, paleecology and systematic evolution of the ancient worms. Fossil evidence shows that the ancient worms have strong point digging ability and some types may have both potential and potential. Although the earliest fossil records of partial solitary bone plate types (such as Hadimopanella) can be traced back to the late Cambrian second stage of the Cambrian, the third order Chengjiang fauna represented the first radiative evolution of the branchial tract. The combination features of the tractable animals are very different. Most of them are endemic molecules of the various biota. Only a few species have a long history delay limit. It shows that the early branchial tracer had better adaptability and rapid differentiation in different living environments. The tracer fossils are produced, indicating that the Southern China East Yunnan shallow sea area is not necessarily the radiant center of the branchial tracts in this period. The Kaili biota produces an important branchial type Ottoia and Sicyophorus., which shows that the Otto body of the Kaili biota has a long 50-80 mm length, and the extended kiss has 25 columns of spines, a short column in the rear, and the trunk width of the trunk. Uniform, dense ring lines, up to 13 /5mm; there is a possible muscle stomach between the pharynx and the intestine; the intestinal wall appears muscle fiber; the trunk of the trunk has 1 pairs of long hind extention muscles. These characteristics are distinctly different from the O. prolifica Walcott in the Burgess Shale biota (Shale), 1911, named the O. guizhouensis Yang, Zhao of the Guizhou Otto worm, Zhao. Et Zhang, 2015. buried O. guizhouensis preserved the evidence that the body is drilling mud, and there is a muddy filling in the intestines, indicating that Ottoia is a kind of inward animal that can freely shuttle in the bottom surface sediments and occasionally live in mud. It was not previously assumed that the cavern was in the U cavern. By analogy with the Chengjiang fauna. The special branchial tracer types, Sicyophorus rara Luo et al., 1999 and Palaeopriapulites parvus Hou et al., 1999, identified the trunk of the cucurbits in the Kaili biota with about 50 column separators, 2-3 rings in the neck and a short tail process at the end, thus establishing the Guizhou cucurbits (new species) S. guizhouensis. Morphological and anatomical evidence shows that Sicyophorus has both morphological structure (kissing and caudate) similar to the branchial tracers, and also the trunk characteristics of the armour (with a column partition), while the curly coiled intestines are different from other annulus, and may be the continuous development of the branchlets during the evolution of the armour to the armour. This article uses TNT software to analyze the system evolution position of O. guizhouensis and S. guizhouensis. The branch tree of the pedigree shows that Ottoia belongs to the Scalidophora group type, and Sicyophorus is located at the bottom of the Scalidophora canopy near the position of the armour, supporting the continuous development of the branchial tractable immature state. In addition, the system evolution position of different species of ancient worms is very different. According to the morphological, anatomical evidence and genealogical analysis, the paper discusses the Xenusia- Scalidophora trunk type Fieldiai of the Urbilateria- leaf feet of bilaterally symmetrical animals and Ancalagonia - the Palaeoscolecida - Louisellia - branchial Priap Ulida - the body configuration characteristics of the representative of each node in the entire evolution line of the Sicyophourus - armour Loricifera of cucurbit cucurbit. It is believed that some of the ancient worms (such as M.yunnanensis) may have similar morphological characteristics to the ancestral types of the molting animals.
【学位授予单位】：西北大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：Q915

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