由美國(guó)加州大學(xué)河濱分校,、麻省理工學(xué)院和其他研究機(jī)構(gòu)組成的一個(gè)國(guó)際研究小組稱，他們發(fā)現(xiàn)了迄今為止動(dòng)物化石記錄的最古老證據(jù),。相關(guān)研究結(jié)果刊登在2月5日出版的英國(guó)《自然》雜志上,。
研究人員在阿曼南部檢查沉積巖時(shí)發(fā)現(xiàn)了異常大量的類固醇，該類固醇為海綿綱的海綿（一種最簡(jiǎn)單的多細(xì)胞動(dòng)物）所特有,，其歷史可追溯到6.35億年前,，即最后的冰河世紀(jì)末期,。
研究人員發(fā)現(xiàn),，化石中的類固醇是海綿細(xì)胞膜上所特有的物質(zhì)。使用目前最先進(jìn)的技術(shù),，他們分析了64種來(lái)自阿曼南部高鹽度沉積盆地的寒武紀(jì)沉積巖樣本,，這里被認(rèn)為是已知的新遠(yuǎn)古時(shí)代化石保存最為完整的一個(gè)地帶。
研究人員認(rèn)為,，這些海綿的發(fā)現(xiàn)證明了多細(xì)胞動(dòng)物生命在寒武紀(jì)大爆發(fā)一億年前就已出現(xiàn),。寒武紀(jì)大爆發(fā)是指距今大約5.3億年前的寒武紀(jì)之初，短短200萬(wàn)年間,，生命進(jìn)化出現(xiàn)飛躍式的發(fā)展,，幾乎所有動(dòng)物的“門(mén)”都在這一時(shí)期出現(xiàn)。因出現(xiàn)大量的較高等生物以及物種多樣性,，于是,，這一情形被形象地稱為生命大爆發(fā)。這一發(fā)現(xiàn)可幫助科學(xué)家重建對(duì)于地球早期生態(tài)系統(tǒng)的認(rèn)識(shí),，并有助于解釋地球早期生物的進(jìn)化過(guò)程,。
負(fù)責(zé)該研究的麻省理工學(xué)院地球科學(xué)助理教授戈登·洛芙說(shuō)：“我們的發(fā)現(xiàn)表明，動(dòng)物的多樣性進(jìn)化比我們?cè)日J(rèn)為的要早得多,。此外,，海綿一般生活在淺水區(qū)的海底，但是隨著時(shí)間推移會(huì)被推入深水區(qū),，這意味著,，6.35億年前，在一些晚成冰期海盆中的淺水中含有濃度大到足以支持簡(jiǎn)單多細(xì)胞生物的溶解氧,。”他稱,，氣候的急劇變化導(dǎo)致了新遠(yuǎn)古時(shí)代（10億年—5.32億年前）的冰川時(shí)期，這可能影響了海洋生態(tài)系統(tǒng)的重組并使海洋的化學(xué)環(huán)境發(fā)生了不可逆的變化,。這為動(dòng)物在海底的生存和進(jìn)化鋪平了道路,。
作為研究的一個(gè)部分，研究人員還為該區(qū)域的底層確定了時(shí)間序列。下一步,，研究人員計(jì)劃對(duì)其他新遠(yuǎn)古時(shí)代的沉積巖中的動(dòng)物性類固醇進(jìn)行甄選,，希望能發(fā)現(xiàn)多細(xì)胞生物大規(guī)模進(jìn)化發(fā)展時(shí)的準(zhǔn)確環(huán)境狀況。（生物谷Bioon.com）
生物谷推薦原始出處：
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).
