动物的起源和寒武纪大爆发：来自中国的化石证据

THE ORIGIN AND CAMBRIAN EXPLOSION OF ANIMALS:FOSSIL EVIDENCES FROM CHINA

近30年来,中国埃迪卡拉纪—寒武纪发现了包括瓮安生物群和澄江动物群在内一系列重要化石群,为揭示动物的起源和寒武纪大爆发过程提供了全球独一无二的古生物学证据。文中全面而简洁地介绍发现于华南埃迪卡拉纪—寒武纪的所有化石群和重要动物化石发现,总结其中特异化石群保存类型和埋藏环境。其中,陡山沱型磷酸盐化胚胎化石群、庙河型宏体碳质膜化石群和牛蹄塘型海绵动物群,以及陡山沱组硅化的动物休眠胚胎化石和宽川铺动物群中"rsten"型化石均是全球这一时期华南独有的特异埋藏化石群。从时空两方面对化石群进行综合分析认为,动物可靠的最早化石记录发现于埃迪卡拉纪早期,成冰纪及其以前的动物化石均存在疑问。动物的起源和寒武纪大爆发经历了从浅水逐步向深水迁移,以及阶段性辐射和灭绝的过程。首先动物经历了在埃迪卡拉纪早期的隐形微体动物早期演化阶段,之后经过以埃迪卡拉型生物为代表的大型复杂化演化阶段,在寒武纪初期发生以梅树村动物群为代表的两侧对称动物和生物骨骼矿化的大爆发,并随后又被以澄江动物群为代表的寒武纪动物群所替代,在筇竹寺期达到了动物造型和生态系统复杂化的高峰。

Earth experienced major biological and environmental revolutions during the Precambrian Cambrian transitional interval,notably,the advent and successive Cambrian explosion of animals following the termination of an extreme ＂Snowball Earth＂ before 635 Ma.In past 30 years,numerous exquisitely preserved fossil biotas （e.g.the Weng’an and Chengjiang biotas） have been discovered from the well-developed and-exposed sedimentary successions of South China,offering an unsurpassed opportunity to decipher the process of the origin and Cambrian explosion of animals.The present paper briefly reviewed all these fossil biotas,their preservations and environments.Except for the Cambrian Chengjiang,Guanshan and Kaili faunas with the characteristic ＂Burgess Shale-type＂ preservation,the following fossil Lagerstttten are unique taphonomic windows,including：1） the early Ediacaran Weng’an biota with the ＂Doushantuo-type＂ preservation of phosphatised embryos;2） the early Ediacaran silicified acritarchs and embryos from the Doushantuo cherts;3） the Ediacaran Lantian,Miaohe,Wenghui and Wulingshan biotas with the ＂Miaohe-type＂ preservation of carbonaceous imprints of macroscopic fossils;4） the late Ediacaran Gaojiashan biota with large pyritized tubular fossils;5） the Kuanchuanpu fauna with preservation of phosphatised embryos and larvae;and 6） the early Cambrian ＂Niutitang-type＂ sponge faunas in black shales.Integrated analyses of all biotas in space and time,we conclude that 1） no unambiguous animal fossils before Ediacaran;2） animal life experienced episodic four radiations and four extinctions across the Precambrian Cambrian transitional interval.The earliest animals emerged as cryptic microfauna during the early Ediacaran,and large complex animals exemplified by the Ediacaran and Gaojiashan biotas appearred during the late Ediacaran.The early Cambrian Meishucun fauna with various small shelly fossils represents the first explosive radiation of bilaterians and biomineralization of animals.The morphospace and ecospace of animals reached their peaks during the Qiongzhusian （～520 Ma） which are evidenced by numerous exquisitely preserved Cambrian biotas,such as the Chengjiang fauan and sponge faunas.In addition,fossils evidence from South China indicates that animals show an onshore-offshore pattern during their early evolution,and first colonization of animals occurred in the Qiongzhusian.