The origin of the Metazoa in the light of the Proterozoic fossil record.
The origin of the Metazoa in the light of the Proterozoic fossil record.
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DOI：
10.2517/prpsj.7.9
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发表时间：
2003-03-01
影响因子：
0.9
通讯作者：
Fedonkin, Mikhail A.
中科院分区：
文献类型：
--
作者：
Fedonkin, Mikhail A.
真核生物（包括多细胞动物或后生动物）的起源通常被认为与大气中氧气含量增加到允许有氧代谢的水平有关。在这里，它表明，生物圈的氧合不是一个许可的条件，而是一个推动复杂的生物系统的形成进化的推动因素。游离氧浓度的增加与其他地史趋势一起，使海洋和大气发生化学反应，使许多化学元素无法移动或无法进行代谢过程。在这方面，特别重要的是海水中重金属浓度的降低，这些重金属表现出高催化能力，并在许多酶中形成活性中心。生物复杂性的增加和生物圈的真核化（真核细胞的起源，异养作用的增加，生物多样性的增加，多细胞生物的兴起，营养链的延长，化学元素的生物循环的加速等）可以被认为是对环境地球化学恶化的进化反应。最近发现的最古老的大型真核生物，如螺旋Grypania（1.9 Ga），组织级组织Horodyskia的项链状殖民生物（1.5 Ga），蠕虫状Parmia（约1.0Ga）和Sinosabellites（800 Ma前）与早期动物起源的“分子钟”模型一致;然而，直到元古宙末，后生动物都局限于海洋碳酸盐带以外的相对寒冷和充氧良好的盆地。在文迪时期，已知的大型和多样的无脊椎动物大多来自硅质海洋盆地。该动物群的特点是底栖种群密度高，在双胚层（例如，三裂体动物门）和三裂体动物（例如，原节动物门）的组织等级以及一些与古生代动物门有关的分类群。在某些后生动物门中，有机骨骼先于矿化骨骼的出现。生境的低温抑制了生物矿化。几乎同时发展的磷酸盐，碳酸盐和硅质骨架在不同的后生动物群在寒武纪开始的约545马前可能与殖民化的温暖的碳酸盐盆地的后生动物。生物矿化门迅速多样化的另一个因素可能是生物多样性迅速增加导致营养链越来越长，以及需要在营养金字塔的顶端进行解毒。骨片和骨针、坚硬的矿化壳和甲壳作为解毒的副产物，立即成为形态进化和生物多样性增长的重要因素，也是捕食者日益增长的压力下强烈选择的对象。在文德纪和寒武纪，后生动物形态生理多样性的爆炸性增长对其他生物群的进化和环境产生了巨大的影响。
Origin of the eukaryotic organisms (including the multicellular animals or Metazoa) is commonly considered to be related to growing oxygen content in the atmosphere up to a level that allows aerobic metabolism. Here it is suggested that oxygenation of the biosphere was not a permissive condition but rather a forcing factor that drove evolution towards the formation of complex biological systems. Growing concentration of free oxygen in conjunction with other geohistorical trends acted to chemically impoverish the ocean and atmosphere and made many of the chemical elements immobile or unavailable for metabolic processes. Of particular importance in this connection was the decreasing concentration in sea water of the heavy metals that demonstrate high catalytic ability and make an active center in many enzymes. Increasing biological complexity and the eukaryotization of the biosphere (origin of the eukaryotic cell, growing role of heterotrophy, increasing biodiversity, rise of multicellular organisms, lengthening of trophic chains, acceleration of biological recycling of the chemical elements, etc.) can be considered as an evolutionary response to the geochemical deterioration of the environment. Recent discoveries of the oldest megascopic eukaryotes, such as spiral Grypania (1.9 Ga), the necklace-like colonial organism of tissue-grade organization Horodyskia (1.5 Ga), vermiform Parmia (about 1.0 Ga) and Sinosabellidites (800 Ma ago) are consistent with the "molecular clock" models on an early origin of animals; metazoans were, however, confined to relatively cold and well oxygenated basins beyond the carbonate belt of the ocean until the end of the Proterozoic. Large and diverse invertebrates of the Vendian Period are known mostly from siliciclastic marine basins. This fauna is characterized by high density of the benthic populations and well established clades both at the diploblastic (e.g., Phylum Trilobozoa) and triploblastic (e.g., Phylum Proarticulata) grades of organization as well as some taxa related to the Paleozoic phyla. An organic skeleton preceded the rise of the mineralized skeleton in some metazoan phyla. Low temperature of the habitats inhibited biomineralization. Almost simultaneous development of the phosphatic, carbonate and siliceous skeletons in different metazoan groups at the beginning of the Cambrian Period some 545 Ma ago could be related to the colonization of the warm carbonate basins by the metazoans. An additional factor for the rapid diversification of the biomineralized phyla could be the growing length of the trophic chains brought about by the rapidly increasing biodiversity and the need for detoxification at the top of the trophic pyramid. Being the byproduct of detoxification, sclerites and spicules, hard mineralized shells and carapaces immediately became an important factor of morphological evolution and growing biodiversity, as well as the object of intensive selection under the growing pressure of predators. Explosive growth of morphophysiological diversity in metazoans during the Vendian and Cambrian had an enormous impact on evolution of other groups of organisms and on the environment.