Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138.
Cold Spring Harb Perspect Biol. 2014 Jan 1;6(1):a016121. doi: 10.1101/cshperspect.a016121.
Eukaryotic organisms radiated in Proterozoic oceans with oxygenated surface waters, but, commonly, anoxia at depth. Exceptionally preserved fossils of red algae favor crown group emergence more than 1200 million years ago, but older (up to 1600-1800 million years) microfossils could record stem group eukaryotes. Major eukaryotic diversification ~800 million years ago is documented by the increase in the taxonomic richness of complex, organic-walled microfossils, including simple coenocytic and multicellular forms, as well as widespread tests comparable to those of extant testate amoebae and simple foraminiferans and diverse scales comparable to organic and siliceous scales formed today by protists in several clades. Mid-Neoproterozoic establishment or expansion of eukaryophagy provides a possible mechanism for accelerating eukaryotic diversification long after the origin of the domain. Protists continued to diversify along with animals in the more pervasively oxygenated oceans of the Phanerozoic Eon.
真核生物在富含氧气的元古代海洋中辐射进化，但在深处通常缺氧。红藻的异常保存化石更有利于冠群的出现，时间超过 12 亿年前，但更古老的（高达 16 亿至 18 亿年前）微化石可能记录了干群真核生物。大约 8 亿年前，复杂的、具有有机壁的微化石的分类丰富度增加，记录了主要的真核生物多样化，其中包括简单的合胞体和多细胞形式，以及广泛的壳，与现存的有壳变形虫和简单有孔虫的壳相当，还有多种多样的鳞片，与今天几个类群的原生生物形成的有机和硅质鳞片相当。从中新元古代开始或扩大的真核生物食性为域起源后很长一段时间内加速真核生物多样化提供了一个可能的机制。随着动物的出现，原生生物在整个显生宙时期氧气更充足的海洋中继续多样化。
