地学前缘 ›› 2020, Vol. 27 ›› Issue (6): 382-412.DOI: 10.13745/j.esf.sf.2020.10.28

• 古脊椎动物与环境 • 上一篇    

Core value of the Chengjiang fauna: formation of the animal kingdom and the birth of basic human organs

SHU Degan, HAN Jian   

  1. 1. 西北大学 地质学系 大陆动力学国家重点实验室与早期生命与环境陕西省重点实验室, 陕西 西安 710069
    2. 西北大学 博物馆, 陕西 西安 710069
  • 收稿日期:2020-07-10 修回日期:2020-09-15 出版日期:2020-11-02 发布日期:2020-11-02
  • 通讯作者: 韩健(1973—),男,研究员,主要从事动物门类起源以及寒武纪生命大爆发研究。
  • 基金资助:

    国家自然科学基金项目 (41672009,41621003,41772010,41720104002);中国科学院战略性先导科技专项B类项目(XDB18000000,XDB26000000) 

Core value of the Chengjiang fauna: formation of the animal kingdom and the birth of basic human organs

SHU Degan, HAN Jian   

  1. 1. Shaanxi Key Laboratory of Early Life and Environments (SKLELE), State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi'an 710069, China
    2. Northwest University Museum, Xi'an 710069, China
  • Received:2020-07-10 Revised:2020-09-15 Online:2020-11-02 Published:2020-11-02
  • Supported by:

    Natural Science Foundation of China(41672009,41621003,41772010,41720104002); The Strategic Priority Research Program of Chinese Academy of Sciences(XDB18000000,XDB26000000)

摘要:

澄江动物群以富含多门类精美软躯体构造化石享誉学界,是寒武纪大爆发主幕的见证者;它亲眼目睹了地球动物树上几乎所有主要门类祖先的首次大聚会。对该动物群30多年的大规模调查研究大体上可以划分为3个阶段。始自1984年的第一个10年(1984—1994年),早期动物树上的基础动物亚界和原口动物亚界的大量门类被发现,然而对后口动物亚界全然无知。第二个10年研究(1995—2005年),基础动物亚界和原口动物亚界中的更多门类被发现;而最重要的进展,是西北大学团队主导的早期后口动物大发现使后口动物亚界的基本框架被构建,由此地球三分动物树首次成型。第三个10年及其以后时期(2005年之后),3个动物亚界中进一步添加了一些新的门类认知;综合20世纪40年代以来对埃迪卡拉生物群、寒武纪第一世和第二世的珍稀动物群研究成果,学界开始思考三分动物树分步成型与多幕式寒武纪大爆发事件的内在关联,提出了三幕式寒武纪大爆发新假说。澄江动物群研究具有多方面的科学价值,包括动物群结构研究,生态环境研究等,然其核心学术价值主要集中在如下两个方面:(1)作为寒武纪大爆发的主幕见证者,澄江动物群首次创建了地球上三分动物树的完整谱系框架。三幕式寒武纪大爆发假说揭示了地球上动物门类由低等到高等、分阶段爆发创造的本质内涵,即历时约0.4亿年的三幕式寒武纪大爆发与动物树阶段性快速成型的内在耦合性。第一幕发生于埃迪卡拉纪晚期,它诞生了众多基础动物亚界门类(包括大量绝灭门类),也可能出现了少量原口动物的先驱分子;第二幕发生于寒武纪的第一世,除了延续基础动物门类的繁盛外,更创生了原口动物亚界里的主要门类(包括蜕皮类和触手担轮类);第三幕发生于寒武纪第二世(以澄江动物群为代表),不仅延续了基础动物和原口动物门类的兴盛,更重要的是诞生了后口动物亚界里的所有门类。至此,整个三分动物树的框架成型,寒武纪大爆发创新事件宣告基本结束。文章还对几个重要动物类群的生物学属性进行了评述。第一鱼昆明鱼目是已知唯一的最古老脊椎动物,而云南虫、海口虫既不是脊椎动物(即高等脊索动物),也不属于低等脊索动物,而是一类特殊的低等后口动物;长江海鞘是可信的始祖尾索动物,它支持了经典的尾索动物起源假说;古虫动物门首创鳃裂构造,对后口动物亚界的起源探索提供了关键信息。(2)澄江动物群具有深刻的人文哲学意义,所发现的古虫动物门创造的“第一鳃裂”,昆明鱼目创造的“第一头脑”“第一脊椎”“第一心脏”,为达尔文在《人类的由来》中关于人类的主要基础器官起源悬案的破解提供了关键证据。澄江动物群承上启下,其各种形态解剖学信息对解读埃迪卡拉生物群以及寒武纪相关化石库中绝大多数生物类型都具有重要的参考价值。

关键词: 澄江动物群的核心贡献, 寒武纪大爆发的本质属性, 动物树三分结构及其三幕式演化成型, 最古老脊椎动物昆明鱼目, 低等脊索动物, 古虫动物门, 蜕皮类群

Abstract:

Well known for its abundant and extraordinary soft-tissue fossils, the Chengjiang fauna has witnessed the main phase of the Cambrian explosion and the first great congress of the ancestors of nearly all major phyla of animals on Earth. The large-scale survey and exploration of the fauna by Chinese paleontologists, partly in collaboration with international scientists, over the past 30 years can be broadly divided into three stages. In the first decade since 1984 (1984—1994), a large number of invertebrates, including basal animals and the protostomes of the early animal tree were discovered, but the subkingdom Deuterostomia was completely unknown. Then in the second decade (1995—2005), the great discoveries of various deuterostomes led to the construction of the basic framework of the Deuterostomia and then to the formation of the tripartite phylogenetic trees of early animals (TPTEA, including basal animals, protostomes and deuterostomes), for the first time. In the third decade (after 2005), the academic community began to think about the internal relationships between the formation of TPTEA and the multi-episode Cambrian explosion, leading to the new hypothesis of the three-episode Cambrian explosion. The Chengjiang fauna is important for deciphering the fauna structure, paleoecological environment, and so on. However, its core academic values mainly rest on two aspects. Firstly, The Chengjiang fauna, as the main phase witness of the Cambrian explosion, has created a nearly complete phylogenetic framework of the TPTEA on Earth for the first time. The three-phase radiation hypothesis reveals the essential connotation of the Cambrian explosion: a step-wise divergent evolution of animals, from basal to highly advanced groups, lasting about 40 million years. In the first phase, it gave birth to a bulk of basal animals (including some now extinct “animal” groups) in the latest Ediacaran, probably including some pioneer protostomes. The second phase took place in the first epoch of the Cambrian period (Terreneuvian), giving rise to the main invertebrate protostomes with a persistent prosperity of basal animals. The third phase proceeded in Cambrian Epoch 2 (represented by the Chengjiang fauna), which not only maintained the prosperity of basal animals and protostomes, but also, more importantly, gave birth to all the main phyla of the subkingdom Deuterostomia. Thus, the rudimental framework of the whole TPTEA has been shaped, with the termination of the major innovation events of the Cambrian explosion. Here, we discussed the evolutionary properties of Ediacaran biota, small shelly fossils and the Chengjiang fauna in the Cambrian explosion with emphasis on the biological properties of several important animal groups. The order Myllokunmingiida is the only known oldest vertebrate, while Yunnanozoon and Haikouella are neither vertebrates nor stem-group chordates but a special group of basal deuterostomes; Cheungkongella is a credible ancestor of the urochordate and it supports the classical hypothesis on the origin of the urochordates; and the gill slits were first invented in the members of the phylum Vetulicolia to provide key information on the origin of the deuterostomes. The second core value of the  Chengjiang fauna is of profound humanistic and philosophical significance: the discoveries of the ‘first gill openings’, ‘first brain’, ‘first vertebrae’ and ‘first heart’ provide the pivotal evidence for solving the unsolved mystery of the origin of the main basic human organs as described in Darwin’s “The Descent of Man”. In addition, the morphological and anatomical information of the Chengjiang fauna can provide important clues for a better understanding of most components of Ediacaran and Cambrian metazoans.

Key words: core value of the Chengjiang fauna, essential properties of the Cambrian explosion, tripartite phylogenetic tree of early animals (TPTEA) and three-phase radiation, oldest vertebrates Myllokunmingiida, basal chordates, Vetulicolia, Ecdysozoa

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