由美国加州大学河滨分校、麻省理工学院和其他研究机构组成的一个国际研究小组称，他们发现了迄今为止动物化石记录的最古老证据。相关研究结果刊登在2月5日出版的英国《自然》杂志上。
研究人员在阿曼南部检查沉积岩时发现了异常大量的类固醇，该类固醇为海绵纲的海绵（一种最简单的多细胞动物）所特有，其历史可追溯到6.35亿年前，即最后的冰河世纪末期。
研究人员发现，化石中的类固醇是海绵细胞膜上所特有的物质。使用目前最先进的技术，他们分析了64种来自阿曼南部高盐度沉积盆地的寒武纪沉积岩样本，这里被认为是已知的新远古时代化石保存最为完整的一个地带。
研究人员认为，这些海绵的发现证明了多细胞动物生命在寒武纪大爆发一亿年前就已出现。寒武纪大爆发是指距今大约5.3亿年前的寒武纪之初，短短200万年间，生命进化出现飞跃式的发展，几乎所有动物的“门”都在这一时期出现。因出现大量的较高等生物以及物种多样性，于是，这一情形被形象地称为生命大爆发。这一发现可帮助科学家重建对于地球早期生态系统的认识，并有助于解释地球早期生物的进化过程。
负责该研究的麻省理工学院地球科学助理教授戈登·洛芙说：“我们的发现表明，动物的多样性进化比我们原先认为的要早得多。此外，海绵一般生活在浅水区的海底，但是随着时间推移会被推入深水区，这意味着，6.35亿年前，在一些晚成冰期海盆中的浅水中含有浓度大到足以支持简单多细胞生物的溶解氧。”他称，气候的急剧变化导致了新远古时代（10亿年—5.32亿年前）的冰川时期，这可能影响了海洋生态系统的重组并使海洋的化学环境发生了不可逆的变化。这为动物在海底的生存和进化铺平了道路。
作为研究的一个部分，研究人员还为该区域的底层确定了时间序列。下一步，研究人员计划对其他新远古时代的沉积岩中的动物性类固醇进行甄选，希望能发现多细胞生物大规模进化发展时的准确环境状况。（生物谷Bioon.com）
生物谷推荐原始出处：
Nature 457, 718-721 (5 February 2009) | doi:10.1038/nature07673
Fossil steroids record the appearance of Demospongiae during the Cryogenian period
Gordon D. Love1,2, Emmanuelle Grosjean3, Charlotte Stalvies4, David A. Fike5, John P. Grotzinger5, Alexander S. Bradley2, Amy E. Kelly2, Maya Bhatia2, William Meredith6, Colin E. Snape6, Samuel A. Bowring2, Daniel J. Condon2,7 & Roger E. Summons2
1 Department of Earth Sciences, University of California, Riverside, California 92521, USA
2 Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 01239, USA
3 Petroleum and Marine Division, Geoscience Australia, Canberra, Australian Capital Territory 2601, Australia
4 School of Civil Engineering and Geosciences, University of Newcastle upon Tyne, Newcastle upon Tyne NE1 7RU, UK
5 Department of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA
6 School of Chemical, Environmental and Mining Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, UK
7 Present address: NERC Isotope Geosciences Laboratory, Keyworth, Nottingham NG12 5GG, UK.
The Neoproterozoic era (1,000–542 Myr ago) was an era of climatic extremes and biological evolutionary developments culminating in the emergence of animals (Metazoa) and new ecosystems1. Here we show that abundant sedimentary 24-isopropylcholestanes, the hydrocarbon remains of C30 sterols produced by marine demosponges, record the presence of Metazoa in the geological record before the end of the Marinoan glaciation (635 Myr ago). These sterane biomarkers are abundant in all formations of the Huqf Supergroup, South Oman Salt Basin, and, based on a new high-precision geochronology2, constitute a continuous 100-Myr-long chemical fossil record of demosponges through the terminal Neoproterozoic and into the Early Cambrian epoch. The demosponge steranes occur in strata that underlie the Marinoan cap carbonate (>635 Myr ago). They currently represent the oldest evidence for animals in the fossil record, and are evidence for animals pre-dating the termination of the Marinoan glaciation. This suggests that shallow shelf waters in some late Cryogenian ocean basins (>635 Myr ago) contained dissolved oxygen in concentrations sufficient to support basal metazoan life at least 100 Myr before the rapid diversification of bilaterians during the Cambrian explosion. Biomarker analysis has yet to reveal any convincing evidence for ancient sponges pre-dating the first globally extensive Neoproterozoic glacial episode (the Sturtian, 713 Myr ago in Oman2).
