動物世界的黎明 The Dawn of Animal World

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動物世界的黎明 The Dawn of Animal World

作者：陳均遠　著

出版社：江蘇科學技術出版社

出版日期：2004年9月1日

ISBN：7534537975

印次：1

版次：1

紙張：銅版紙精裝本全彩印刷

語言: 簡體中文版

書本尺寸: 29.4公分長 x 21.9公分寬 x2.9公分厚

頁數: 366頁

重量: 1.76公斤

內容提要

位於中國大陸的澄江化石, 一直都是因為(寒武紀大爆發)的重要研究地點, 所有的化石都是中國大陸列為一級保護的研究對象, 保護甚嚴, 也因此, 它在國際化石收藏者的眼中卻變成是一定要擁有的瑰寶。 今天, 很高興我們能拜讀陳均遠先生的大作, 即使沒有化石相伴, 相信各位愛石者也能翻翻這本書, 而幻想一下身處於寒武紀大爆發之地的感受吧?!

這本書(動物世界的黎明)採用了大量的第一手化石材料和栩栩如生的生物復原圖，“觸摸”那個遠離我們而去的遠古動物世界。書中許多化石為首次披露。這些關於動物世界黎明的化石不僅牽動了一個包括脊椎動物在內當含博大的生命世界，而且它們本身展現了一幅關於生命演化的巨幅歷史畫卷。在長達5000萬年中，動物世界的黎明先後經歷了甕安大輻射、伊迪卡拉大輻射、梅樹村大輻射和帽天山大輻射。以上4次連續發生的輻射事件構成了一個奇特的演化過程，這個過程稱為“點斷輻射”，它與以後5億多年以“點斷平衡”為主導的演化過程不同。
　　發生在5億多年前壯闊而神奇的生命世界在寒武紀突然的崛起稱為“寒武紀大爆發”，這一事件困惑了達爾文以來一個多世紀，在當今仍是一個重大科學難題。
　　本書首次系統展現了來自5.8億年前中國貴州甕安動物群胚胎、幼蟲和成體化石，使我們走進一個比“寒武紀大爆發”世界更加古老的“伊甸園”，為動物世界的黎明添加了序曲。
　　這些來自貴州甕安“伊甸園”有胚胎、幼蟲和成體化石展現了地球最古老的先民如何在受精之後進行細胞分裂，以及一個複雜生命體是如何從一個受精卵誕生的過程。精美無比的雲南澄江、昆明附近寒武紀大爆發主幕的化石為我們充當了“溯源之旅”的使者，引導我們零距離探索當今世界的一個偉大起點，一個遠離我們而去的壯闊而神奇的世界。

作者簡介

陳均遠，國際知名古生物學家和深化生物學家，中國科學院南京地質古生物研究所研究員，南京大學兼職教授。1960年畢業于西北大學，1981年以來先後多次赴美國、加拿大、瑞典和臺灣等有關大學和博物館任客座教授和研究員。在科學, 自然, 美國科學院院刊等學術刊物上發表論文100餘篇，出版書和專著10餘部。曾多次獲得國家、中國科學院和江蘇省自然科學重要獎項，其中包括2003年度國家自然科學一等獎、1998年度中國科學院特等獎和1998年度香港求實基金會科學技術集體成就獎。
　　他興趣廣泛，自1983年以來兩次參加了加拿大布林吉斯葉岩化石群的實地發掘。1987年以來更是滿懷激情地開始了動物世界“溯源之旅”。他認為科學本身就是一種文化，是文明世界的重要支柱。他還認為科學家的目光不該是冷酷而狹窄的，而應該是把自己看成是人類中普通的一員，擁有其他人所具有的困惑，諸如“我們來自何方？”“我們為什麼在這裏？”“我們孤獨嗎？”

目錄

前言
關於我們的行星
　我們行星的簡史
　地球生命起源之謎
　生命與水
　人類是否獨一無二？
　深時
　時時變化的生命舞臺
　生命大家庭
動物世界的黎明和點斷輻射演化
　甕安大輻射迎來了動物世界黎明的曙光
　一次失敗了的輻射：伊迪卡拉大輻射
　寒武紀大爆發的序幕——梅樹村大輻射
　帽天山大輻射——寒武紀大爆發的主幕
甕安大輻射
　生命之河溯源之旅
　動物黎明之鄉——甕安
　重建伊甸園
梅樹村大輻射的化石
　梅樹村大輻射的背景
　寒武紀大爆發序幕的記錄
　解讀梅樹村大輻射的小殼化石
　十分奢侈的表面骨骼裝飾
　梅樹村大輻射的胚胎
帽天山大輻射的化石　
　帽天山大輻射是一部無字天書：帽天山葉岩動物群的成因
　鮮為人知的發現
　備受世人矚目的大發現
　化石產地
　寒武紀大爆發主幕的海綿
　寒武紀大爆發主幕的刺細胞動物　
　開腔骨（chancelloriids）化石及其親緣關係
　寒武紀海洋中的海胡桃
　在泥底內生活的球早期先民——曳鰓動物　
　帽天山大輻射的昆蟲
　寒武紀大爆發主幕可穎的多毛類
　帶殼角錐狀古螺——軟舌螺
　點頭蟲狀生物——高足杯蟲
　在後口與原口動物過渡地帶的生物——解手冠動物　
　水母狀具觸手冠生物
　在後口與原口動物過渡地帶的一個孤支——箭蟲　
　帽天山大輻射的步行者
　節肢動物　
　在金字塔基底的微型節肢動物　
　三葉狀節肢動物Trilobitomorphs
　原蛪肢動物　
　巨型原蛪肢動物——寒武紀巨怪奇蝦類（Anomalocarids）
　脫離以步行為演化主線的泛節肢動物孤支——古蟲類
　尾索動物　
　脊椎動物之源
參考文獻
主題索引

動物世界的黎明 The Dawn of Animal World

Cambrianexplosion and some arthropods from the Early Cambrian Chengjiang Lagerstätte,Yunnan, South China

1. Cambrian explosion

Cambrian explosion designates the sudden appearance of a majority ofanimal phyla nearly at the base of Cambrian. It has been regarded as anunprecedented evolutionary renovation in life history, which took place mostrapidly and universally, and had a great impact on the animal evolution. Thedebate on such subject has never been ceased since it was first recognized byscientists. In the past decade, data from the results of multidisciplineresearches, on the one hand, allow us to understand this event morecomprehensively and precisely, on the other, the focus of conflictinghypotheses is becoming increasingly evident.

Cambrian explosion manifests an universality of revolution. Not only mostmetazoan phyla made their debut at the earliest Cambrian, but also the fossilrecord like calcareous metaphyte flora and acritarch change dramatically nearlyat the same time. Additionally, the evolutionary change in lithosphere andatmosphere, such as the rearrangement of continents, true pole wander,paleoclimate, geochemistry of the ocean and the partial oxygen content, wascorresponding well with the biological big bang in time. The isotopicchronology with high resolution indicate that the time span from the firstappearance of small shelly fossils to the diversify of animal phyla atAtdabanian is less than 20 Ma and major animal phyla actually appeared within10 Ma between. Therefore it is an unexpectedly rapid event. Besides, Cambrianexplosion is not single event but a series of radiations of animals,episodically continued.

However, molecular biology suggests that metazoans diversified deep inthe Precambrian. Early animals may be tiny, lack of hard parts, larva-like orresemble miofauna. Neither have they potential to be fossilized, nor do maketracks. Here I propose three scenarios to interpret this conflict. (1). If thelarva-form or miofauna hypothesis is true, ancestors to Cambrian metazoanslived before the Vendian. In this case, these ancestors were not capable ofmaking the sorts of trace fossils found in Vendian and must have been eithertiny or flat or both. Trace fossils in Vendian reflect the first increasing ofanimal body. The Cambrian “explosion” is largely a biomineralization, must berelated to some pervasive environment change, e. g. geochemistry of seawaterand an increase in atmospheric oxygen content above some critical constraint tosupport a race of predator and prey. Abrupt appearance of diverse animalfossils at the base of Cambrian, then, represents the first record of animalsrather than their origination. (2). Another possibility is that the lastancestor common to bilaterians could have been lived nearly 600Ma years ago andlineage divergence and body formation were spread through the 50-million-yearinterval between the early traces and the Cambrian “explosion” (600-543Ma).Cambrian “explosion” involved a further rise of major morphological innovationsand a universal biomineralization. (3). The final scenario is a real explosion.Lineage divergence of bilaterians phyla took place rapidly between 543-525million years ago. In this case the Neoproterozoic traces were produced byanimals that predated the last ancestor common to protostomes anddeuterostomes.

Choosing between these three hypotheses is difficult at presently. Eachhas its own limitation and is challenged by another. A new phylogenetic tree ofanimals may throw a new light on this evolutionary enigma. The typicaltraditional phylogenetic tree separates the animals with bilateral symmetryinto three groups, i. e. acoelomates, pseudocoelomates and coelomates. Onegeneral feature of this tree is that there tends to be an increase incomplexity from the bottom to top. A revised phylogenetic tree based on 18SrDNA sequence divided bilaterians into two large groups, namely, protostomesand deuterostomes. The protostomes further is split into two superphyla:Ecdysozoa and Lophotrochzoa. More surprisingly, the acoelomate platyhelminthsand nemertines were not at the bottom of tree but were raised within the superphylum Lophotrochzoa. Furthermore, the aschelminths or pseudocoelomates werenot a monophyletic group. Rotifers and gastrotiches were grouped within theLophotrochzoa, and kinorhynchs, priapulids and nematodes, together witharthropods, form another protostome superphylum Ecdysozoa (including moultinganimals). This phylogenetic tree was supported by a phylogenetic analysis basedon Hox genes. On the other hand, the intra-Lophotrochzoa and intra-Ecdysozoaphylogeny remains quite uncertain at the movement and might turn out to be verydifficult to solve if the diversification within each of these clades indeedcorresponds to a rapid radiation. This topology of the tree suggests a newinterpretation of the Cambrian explosion. Briefly, instead of a singleradiation, the topology suggests that at least three independent eventscorresponding to the diversification of the lophotrochzoans, ecdysozoans anddeuterostomes have occurred at short time interval. The ancestor of eachsuperphylum and ancestor common to them may have occurred in the latestPrecambrian but were poorly diversified.

2. Chengjiang Lagerstätte

Cambrian Lagerstätten, yielding soft-bodied fossils, are the bestmanifestation of Cambrian explosion. The Middle Cambrian Burgess Shale,discovered at the early of the last century, has long been considered as one ofthe best windows on the Cambrian explosion. Since 1980s, researches on theEarly Cambrian Chengjiang Lagerstätte (Yunnan,South China) and the Sirius Passet Lagerstätte (Peary Land, North Greenland) indicate that the complexity of body plan, anddiversity and abundance of animals in the Burgess Shale appeared in the EarlyCambrian. The Cambrian explosion is more dramatic than we previously thought. Theinvestigation of the Chengjiang Lagerstätte has made a great breakthrough inthe past two years. Especially, the discovery of many new localities largeenhanced the research in this subject. New localities yield new animals, makinga comprehensive understanding possible as well as providing the most importantclues for us tracing the origin of the major animal phyla. At the same time, italso makes it possible for analyzing the distribution and correlation offaunas. (1). The discovery of diverse chordates and lower vertebrates not onlyput the origin of vertebrates earlier in the Cambrian explosion, but alsolargely expanded our knowledge of the evolutionary big bang. (2). Some animalphyla, lacking hard parts, have no fossil record in Cambrian. Fossil Lagerstättelike the Chengjiang most probably contain such taxa. Yunnanozoon, interpreted as an enteropneuste hemichordate, belongsto one of them. (3). The occurrence of new body plans like Vetulicolida and Cambrotentacus, which were distinctivefrom extant and fossil taxa known, firmly supports the hypothesis that therewere more body plans in Cambrian. It is estimated that there were 70-100 animalphyla in Cambrian. (4). Three fossil assemblages have been recognized in theChengjiang Lagerstätte, which are distributed in two different microfacies.

In addition, most taxa described from the Cambrian Lagerstätte aremonotypic genera, represented by only one species. Assigning them to the taxaknown blow the phylum appears to be difficult, although it is no problem toclassify in phylum level. The sudden appearance of diverse body plans and eachof them represented by fewer species suggest a framework of higher disparityand lower diversify. It is, therefore, very likely that the divergence ofanimals in higher level of classification predates the diversification inspecies level. This pattern conflicts with the gradualism and the punctuatedequilibrium. Advocators of the both theories hold such a view that the originof body plan is a result of the increase of the diversity in species level.Therefore, the increase of diversity should predate the disparity. However,fossil record indicate that not only most phyla of animals make theirappearance at the very beginning of Cambrian, there are also many of body plansnot extending to the later era. If the fossil record is true, both thegradualism and the punctuated equilibrium can not interpret the suddenappearance of diverse body plans in the Cambrian. Therefore, it is reasonableto assume that the Cambrian explosion reflects the early evolution ofbilaterians, a stage that a great number of body plans freely originated formore ecospaces, triggered by dramatic environment changes. The framework ofanimal evolution was formed at this time. Subsequent evolution has beencontinued on this basis. Some adapted to an environment diversified even more,other shortly become extinct for their inadaptability. Once the framework isformed, each body plan will do his best to keep the shape. Morphologicalchanges are rather limited. This is the stasis common in biology. In fact, fewbody plans originated in post Cambrian.

3. The Chengjiang arthropods

Arthropods have conquered land, sea and air, andmake up over three-fourths of all currently known living and fossil animals, orover one million species in all. Therefore, arthropod diversity, as measured bynumber of taxa, range of body forms, and ecological variety, is one of thegreat manifestations of animals on Earth. Fossils from Lagerstätten show thatthe arthropod was considerably diversified during its earliest stage ofevolution in the Cambrian. Advances recently achieved in cladistics, molecularbiology, comparative anatomy, embryology and paleontology make more and moreauthors favoring a monophyletic arthropod origin. If it is true, all arthropodswere derived from a common ancestor. That left a question of what the ancestorof the arthropods looked like. A great number of hypothetical ancestral arthropodswere proposed, but little consensus existed. The ancestral arthropod hastraditionally been envisaged as an animal similar to annelids but havingcuticlized exoskeletons and jointed appendages. This hypothesis is largelybased on the theory of Articulata, considering annelids as a sister group.However, more recent analysis based on 18S rDNA put Annelida and Arthropodainto two large different subgroups of protostomes, i. e. Lophotrochozoa andEcdysozoa respectively. Arthropods are not closely related with annelids.Arthropods are dominated in the Chengjiang Lagerstätte, whose age is within thesecond trilobite zonation: Eoredlichia-Wutingaspis.The Chengjiang arthropods are, therefore, the earliest record of arthropoddiversity. Among them there is a small larva-like arthropod, which wasconsidered to be protaspis of naraoiids by many authors. The discovery of agreat number of well-preserved specimens from many of the new localities hasallowed the original study to be revised. This new material provides much morecomplete information on its morphology. The relatively large size, stablemorphology and the unusual structure of appendages indicate that thesespecimens represent adults of a new arthropod: Primicaris larvaformis. The larva-like outline is considered tohave arisen by the heterochronic process of progenesis. In addition, thisanimal displays primitive aspects of bodyplan and limb morphology that suggesta basal position within arthropods. Therefore, I propose that the ancestralarthropod bear antenna-like biramous appendages.

Professor Hou Xiangguang has done well on theChengjiang arthropods. His detailed descriptions on arthropods constitute abasis for us to continue the research. Here I focus on some Chengjiangarthropods, showing evolutionary significance. Nine genera and species aredescribed and discussed, including three new genera and six new species.

Eurycephalus epicharis gen. et sp. nov.

Kleptothule sp.

Molaria mania sp. nov.

Naraoia pammon Simonetta and Delle Cave, 1975

Primicaris larvaformis gen. et sp. nov.

Pseudonaraoia dapotouensis sp. nov.

Pygmaclypeatus daziensis gen. et sp. nov.

Sidneyia sinica sp. nov.

Urokodia aequalis Hou et al., 1989

Key words: Cambrianexplosion; Chengjiang Lagerstätte; Animal evolution; Arthropoda