Putative sponge biomarkers in unicellular Rhizaria question an early rise of animals
Putative sponge biomarkers in unicellular Rhizaria question an early rise of animals
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DOI：
10.1038/s41559-019-0806-5
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发表时间：
2019-03
影响因子：
16.8
通讯作者：
B. Nettersheim;J. Brocks;Arne Schwelm;J. Hope;F. Not;M. Lomas;C. Schmidt;R. Schiebel;E. Nowack;P. De Deckker;J. Pawłowski;S. Bowser;I. Bobrovskiy;K. Zonneveld;M. Kučera;M. Stuhr;C. Hallmann
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文献类型：
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作者：
B. Nettersheim;J. Brocks;Arne Schwelm;J. Hope;F. Not;M. Lomas;C. Schmidt;R. Schiebel;E. Nowack;P. De Deckker;J. Pawłowski;S. Bowser;I. Bobrovskiy;K. Zonneveld;M. Kučera;M. Stuhr;C. Hallmann
动物的诞生仍然是生命进化过程中最神秘的里程碑之一。化石脂质 24-异丙基胆甾烷和 26-甲基豆甾烷被认为可以诊断海绵海绵——可以说是现存最古老的动物群。这些生物标志物在 635-5.41 亿年 (Myr) 前的埃迪卡拉纪沉积物中广泛存在且相对丰度较高，被视为动物在寒武纪快速辐射之前约 100 Myr 就已达到生态重要性的证据。在这里，我们表明，24-异丙基胆甾烷和26-甲基豆甾烷前体的生物合成在早期分支的单细胞根藻中很常见，异养原生生物在现代海洋的营养循环和碳输出中发挥着重要作用。我们的研究否定了这些碳氢化合物作为海绵生物标志物的可能性，将最古老的动物证据放在了更接近寒武纪大爆发的位置。大约 535 密尔年龄的寒武纪二氧化硅六针针现在代表了最古老的诊断海绵遗骸，而大约 558 密尔年龄的狄金森尼亚和金贝拉（埃迪卡拉生物群）为动物的出现提供了最可靠的证据。捕食性原生生物的增殖可能是新元古代晚期生态变化的原因之一，包括藻类的兴起、复杂营养关系的建立以及宏观动物随后上升所需的浅水栖息地的氧化。
The dawn of animals remains one of the most mysterious milestones in the evolution of life. The fossil lipids 24-isopropylcholestane and 26-methylstigmastane are considered diagnostic for demosponges—arguably the oldest group of living animals. The widespread occurrence and high relative abundance of these biomarkers in Ediacaran sediments from 635–541 million years (Myr) ago have been viewed as evidence for the rise of animals to ecological importance approximately 100 Myr before their rapid Cambrian radiation. Here we show that the biosynthesis of 24-isopropylcholestane and 26-methylstigmastane precursors is common among early-branching unicellular Rhizaria—heterotrophic protists that play an important role in trophic cycling and carbon export in the modern ocean. Negating these hydrocarbons as sponge biomarkers, our study places the oldest evidence for animals closer to the Cambrian Explosion. Cambrian silica hexactine spicules that are approximately 535 Myr old now represent the oldest diagnostic sponge remains, whereas approximately 558-Myr-oldDickinsoniaandKimberella(Ediacara biota) provide the most reliable evidence for the emergence of animals. The proliferation of predatory protists may have been responsible for much of the ecological changes during the late Neoproterozoic, including the rise of algae, the establishment of complex trophic relationships and the oxygenation of shallow-water habitats required for the subsequent ascent of macroscopic animals.