寒武纪生命大爆发新解与地球海洋动物生态系统建立

New perspectives on Cambrian Explosion:construction of the first animal consumer-driven marine ecosystem on Earth

寒武纪大爆发是地球历史上唯一的动物门类创生事件,导致所有现生动物门类几乎同时在寒武纪早期海洋中首现——地球动物树成型。显生宙之后的其他重大地质事件甚至动植物登陆过程中地球再无新的动物门类出现。因此,寒武纪大爆发既是重大生命事件也是地质事件,成为地球宜居性演化研究的关键。国内外许多研究团队和学者从不同的视角对寒武纪大爆发做了深入探索和思考,取得了系列成果和认识。基于生命物质的组织层次(organismal hierarchical level)及其地质背景,本文提出了地球早期生命宏演化包括分子水平进化、细胞水平进化和组织水平进化三大宏演化阶段。据此,认为寒武纪大爆发的实质是原生生物细胞群“组织化”的必然结果,并提出寒武纪动物大爆发组织“拼图”新假说(Lego Blocks Hypothesis)。寒武纪动物大爆发的突发性和爆发性是在现代板块构造体制建立和异养型消费者生态位空缺的背景下,在全球圈层联动、全球海洋微生物和化学循环的促使下,部分真核细胞发生“分化和特化”形成原始组织后,快速“拼图组装”的必然结果。期间,地球海洋生态空间(生态位)多样性剧增、动物消费者生态位空缺及其导致的古地理和生殖隔离,成为寒武纪早期动物门类爆发的生态动力和生物发育内在需求。罗迪尼亚超大陆裂解和冈瓦纳大陆形成过程中,全板块深俯冲为标志的现代板块构造体制的建立,导致全球圈层联动和全球海洋微生物化学循环,进一步加速了动物门类的生态扩张。显生宙盘古大陆演化和原、古、新特提斯洋发育过程中全球海洋生态空间多样性阈值的稳定甚至减少,可能成为寒武纪大爆发后地球海洋再无新的动物门类出现的环境条件和地质背景制约。

The Cambrian Explosion represents one of the most profound phases in the history of life,with nearsimultaneous emergence of most modern animal phyla,including all Bilateria.Since this time,the proliferation of animals across all ecospaces,including terrestrial environments,suggests that the Earth has become increasingly habitable for animal life.Along with the sudden appearance of essentially all the readily fossilized major animal groups,the Cambrian Explosion(540–510 Ma) also resulted in the first appearance of macro-consumers and complex trophic interactions,and established patterns of emergence and diversification that define the modern animal tree of life.Following the Cambrian,despite numerous major geological events and the migration of both plants and animals into the terrestrial realm,there is no apperance of new animal phyla.The Cambrian Explosion can therefore be considered a unique event in the history of life,representing both a key transition in global habitability and the starting point for animal consumer-driven marine ecosystems.Previous work by multiple research teams,from both China and abroad,has explored the Cambrian Explosion from many different perspectives,and has markedly increased our understanding of this major evolutionary event.Based on this work,combined with research progress on Precambrian biotas,this paper proposes three macroevolutionary phases in the evolution of early life.Each phase is defined by both organismal “hierarchical level” and geological settings,with the Cambrian Explosion representing the culmination of the three phases.These three phases are:molecular-level evolution during the origin of early continents,cellular-level evolution along with the supercontinent evolution of Nuna(Columbia) and Rodinia,and tissue-level evolution coupled with the early assembly and breakup of Pangea.At the earliest stages of Earth's history,macro-level prokaryotes,derived from protocell-forming molecules,first formed(Molecular Phase).The first appearance of eukaryotic cells,derived from prokaryotes,represents the next milestone in biological evolution(Cellular Phase).The subsequent emergence of multicellular eukaryotes(metazoans) represents the third and final phase(Tissues Phase).Combined with the advent of multicellularity comes a revolution in body-plan organization,facilitated by the innovative capacity to develop specialized tissues.This includes the spontaneous development of mineralized epithelial exoskeletons and connective tissue endoskeletons.Based on these developments,a ‘Lego Blocks' hypothesis for the Cambrian Explosion is proposed,driven by the initiation of the modern plate tectonic regime characterized by full-plate deep subductions and the associated changes in Earth's multi-sphere interactions,and bio-litho-atmospheric cycles during Rodinia breakup and Gondwana assembly.During this period of geological disruptions,the diversity of marine niches expanded,resulting in both accelerated phylogenetic diversity and ecological expansion,as organisms developed both a wide range of specialized biological tissues and tissue arrangements to exploit the newly available vacant niche space.The failure of new animal phyla to emerge following the Cambrian Explosion can thus possibly be explained by both a maximization of potential organismal complexity and the relative stabilization of ecospaces.Following the breakup of the Neoproterozoic supercontinent Rodinia,major palaeogeographic changes during the Phanerozoic are limited to the opening and closing of the NeoPaleo-Tethys Ocean,neither of which created novel ecological niches not previously in existence.