Mills Daniel B, Francis Warren R, Canfield Donald E
Department of Biology, University of Southern Denmark, Odense, Denmark.
Emerg Top Life Sci. 2018 Sep 28;2(2):289-298. doi: 10.1042/ETLS20170160.
The Neoproterozoic Era (1000-541 million years ago, Ma) was characterized by dramatic environmental and evolutionary change, including at least two episodes of extensive, low-latitude glaciation, potential changes in the redox structure of the global ocean, and the origin and diversification of animal life. How these different events related to one another remains an active area of research, particularly how these environmental changes influenced, and were influenced by, the earliest evolution of animals. Animal multicellularity is estimated to have evolved in the Tonian Period (1000-720 Ma) and represents one of at least six independent acquisitions of complex multicellularity, characterized by cellular differentiation, three-dimensional body plans, and active nutrient transport. Compared with the other instances of complex multicellularity, animals represent the only clade to have evolved from wall-less, phagotrophic flagellates, which likely placed unique cytological and trophic constraints on the evolution of animal multicellularity. Here, we compare recent molecular clock estimates with compilations of the chromium isotope, micropaleontological, and organic biomarker records, suggesting that, as of now, the origin of animals was not obviously correlated to any environmental-ecological change in the Tonian Period. This lack of correlation is consistent with the idea that the evolution of animal multicellularity was primarily dictated by internal, developmental constraints and occurred independently of the known environmental-ecological changes that characterized the Neoproterozoic Era.
新元古代（10亿至5.41亿年前）的特征是环境和进化发生了巨大变化，包括至少两次广泛的低纬度冰川作用、全球海洋氧化还原结构的潜在变化以及动物生命的起源和多样化。这些不同事件之间的相互关系仍然是一个活跃的研究领域，特别是这些环境变化如何影响动物的最早进化以及受到其影响。动物多细胞性估计在拉伸纪时期（10亿至7.2亿年前）进化而来，是至少六次独立获得复杂多细胞性的事件之一，其特征包括细胞分化、三维身体结构和活跃的营养物质运输。与其他复杂多细胞性的情况相比，动物是唯一从无壁、吞噬性鞭毛虫进化而来的进化枝，这可能对动物多细胞性的进化施加了独特的细胞学和营养限制。在这里，我们将最近的分子钟估计与铬同位素、微古生物学和有机生物标志物记录的汇编进行了比较，表明到目前为止，动物的起源与拉伸纪时期的任何环境 - 生态变化没有明显关联。这种缺乏相关性与动物多细胞性的进化主要由内部发育限制决定且独立于新元古代特征性的已知环境 - 生态变化这一观点一致。
