Causes and consequences of the Cambrian explosion  

作　　者：ZHANG XingLiang SHU DeGan 

机构地区：[1]State Key Laboratory of Continental Dynamics and Department of Geology, Northwest University [2]Early Life Institute, Northwest University

出　　处：《Science China Earth Sciences》2014年第5期930-942,共13页中国科学（地球科学英文版）

基　　金：supported by National Basic Research Program of China (Grant No. 2013CB835000);National Natural Science Foundation of China (Grant Nos. 40925005, 41272036);the "111 Project" (Grant No. P201102007);the key project from the State Key Laboratory of Continental Dynamics, Northwest University

摘　　要：The Cambrian explosion has long been a basic research frontier that concerns many scientific fields. Here we discuss the cause-effect links of the Cambrian explosion on the basis of first appearances of animal phyla in the fossil record, divergence time, environmental changes, Gene Regulatory Networks, and ecological feedbacks. The first appearances of phyla in the fos- sil record are obviously diachronous but relatively abrupt, concentrated in the first three stages of the Cambrian period （541- 514 Ma）. The actual divergence time may be deep or shallow. Since the gene regulatory networks （GRNs） that control the de- velopment of metazoans were in place before the divergence, the establishment of GRNs is necessary but insufficient for the Cambrian explosion. Thus the Cambrian explosion required environmental triggers. Nutrient availability, oxygenation, and change of seawater composition were potential environmental triggers. The nutrient input, e.g., the phosphorus enrichment in the environment, would cause excess primary production, but it is not directly linked with diversity or disparity. Further in- crease of oxygen level and change of seawater composition during the Ediacaran-Cambrian transition were probably crucial environmental factors that caused the Cambrian explosion, but more detailed geochemical data are required. Many researchers prefer that the Cambrian explosion is an ecological phenomenon, that is, the unprecedented ecological success of ruetazoans during the Early Cambrian, but ecological effects need diverse and abundant animals. Therefore, the establishment of the eco- logical complexity among animals, and between animals and environments, is a consequence rather than a cause of the Cam- brian explosion. It is no doubt that positive ecological feedbacks could facilitate the increase of biodiversity. In a word, the Cambrian explosion happened when environmental changes crossed critical thresholds, led to the initial formation of the meta- zoan-doruinated ecosystem through a series of knThe Cambrian explosion has long been a basic research frontier that concerns many scientific fields.Here we discuss the cause-effect links of the Cambrian explosion on the basis of first appearances of animal phyla in the fossil record,divergence time,environmental changes,Gene Regulatory Networks,and ecological feedbacks.The first appearances of phyla in the fossil record are obviously diachronous but relatively abrupt,concentrated in the first three stages of the Cambrian period(541–514 Ma).The actual divergence time may be deep or shallow.Since the gene regulatory networks(GRNs)that control the development of metazoans were in place before the divergence,the establishment of GRNs is necessary but insufficient for the Cambrian explosion.Thus the Cambrian explosion required environmental triggers.Nutrient availability,oxygenation,and change of seawater composition were potential environmental triggers.The nutrient input,e.g.,the phosphorus enrichment in the environment,would cause excess primary production,but it is not directly linked with diversity or disparity.Further increase of oxygen level and change of seawater composition during the Ediacaran-Cambrian transition were probably crucial environmental factors that caused the Cambrian explosion,but more detailed geochemical data are required.Many researchers prefer that the Cambrian explosion is an ecological phenomenon,that is,the unprecedented ecological success of metazoans during the Early Cambrian,but ecological effects need diverse and abundant animals.Therefore,the establishment of the ecological complexity among animals,and between animals and environments,is a consequence rather than a cause of the Cambrian explosion.It is no doubt that positive ecological feedbacks could facilitate the increase of biodiversity.In a word,the Cambrian explosion happened when environmental changes crossed critical thresholds,led to the initial formation of the metazoan-dominated ecosystem through a series of knock-on ecological processes,i.e.,"ecological snowball"eff

关 键 词：Cambrian explosion dGRNs GONDWANA environmental changes ecological snowball 

分 类 号：Q911[天文地球—古生物学与地层学]