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[摘要]
人类探索认识寒武纪大爆发的过程先后经历了神创论、渐变论和爆发式演化思想的影响, 形成了越来越接近真理的重要科学认识。寒武纪大爆发本质上是动物门类的大爆发, 同时伴随着属种多样性的增长、体型增大、生物矿化以及海洋生态系统的重大变革。寒武纪大爆发是多因素制衡的自然历史过程, 任何单因素的内、外因驱动假说都不足以解释寒武纪大爆发的复杂过程。分子遗传基础和宜居环境分别是寒武纪大爆发的内在和外在必要条件, 但不是必要充分条件。因此, 寒武纪大爆发, 与其他所有生命演化事件一样, 必须通过生态作用实现。寒武纪大爆发是在氧气和其他资源不太受限、环境多变、生态荒芜的外在条件下, 基因发育调控系统预先高配的内在条件下, 发生的动物门类大爆发。在埃迪卡拉纪晚期, 多细胞的文德生物与动物采取了不同的体型发育策略和演化途径, 共享海底两千万年后, 文德生物灭绝。此后, 动物在寒武纪最初的两千万年间快速分异演化, 产生了大量演化结局各不相同的动物门类, 生态适应策略同步分化, 形成了以动物为主导的海洋生态系统, 踏上显生宙的演化征程。目前对寒武纪大爆发的探索和研究存在着偏向性或局限性, 主要关注动物门类演化和生存环境氧化还原条件, 没有将海洋生态系统作为统一整体开展全面系统的研究工作。未来探索有必要在全球范围内开展广泛全面的研究工作, 揭示寒武纪大爆发时期海洋生态系统的时空演变。
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[Abstract]
The journey to understand the Cambrian explosion started with Creation, was subsequently succeeded by Darwinism, and became increasingly impacted by the theory of explosive evolution. The Cambrian explosion by nature is an explosion of animal body plans alongside episodic biomineralization, pulsed change of generic diversity, body size variation, and increase of ecosystem complexity. It is a polythetic event in natural history and manifested in many aspects. No simple, single cause can explain the entire phenomenon. Intrinsic and extrinsic causes were extensively discussed but they are merely prerequi-sites for the Cambrian explosion. Without the molecular evolution, there could be no Cambrian explosion. However, the de-velopmental system alone is insufficient to explain Cambrian explosion. Time-equivalent environmental changes were often considered as extrinsic causes, but the time coincidence is also insufficient to establish causality. Like any other evolutionary event, it is the ecology that makes the Cambrian explosion possible though ecological processes failed to cause a burst of new body plans in the subsequent evolutionary radiations. While the Cambrian explosion did take place under circumstances when the world oceans became habitable for various forms of animals, the developmental Gene Regulatory Networks (GRNs) were sufficiently complex for constructing complex forms, and resource supply was less restricted. It seems that opportunities were in every corner! Early metazoans shared seafloors with vendobionts for the last 20 million years of the Ediacaran, although their ecological relationships are less known. Metazoans followed the path of evolving organs and sys-tems, developing orderly repetition of body parts, and attempting possibilities, which enable the evolution of morphological, physiological, ecological variations and complexity. While vendobionts kept their less differentiated body designs, tis-sue-grade organization, and probably osmotic physiology. Consequently, Ediacarans died off at the end of their era for un-known reasons. Thereafter metazoans rapidly diversified and generated numbers of phylum-rank stem or crown lineages with different fates. The Cambrian explosion ultimately resulted in the critical transition from microbially-dominated ecosys-tems in the Precambrian to metazoan-dominated ecosystems in the Phanerozoic. However, the temporospatial pattern of eco-systems during the Cambrian explosion is poorly understood, largely because our current knowledge is biased in metazoan evolution and redox conditions, and thus insufficient to reconstruct an ecosystem that is an integrative entirety of biotic and abiotic components. Therefore, we proposed a facies-dependent integrative approach as a working hypothesis toward a more comprehensive understanding of ecosystem evolution during the Cambrian explosion.
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