生物谷报道：来自美国弗吉尼亚理工大学（Virginia Polytechnic Institute and State University，生物谷注）的研究人员在生物进化研究方面取得了突破性的研究进展：他们发现地球上复杂的生命体经过了两次，而不是一次“爆炸”而迅速繁衍。这一研究成果公布在Science杂志上。
文章的通讯作者是来自弗吉尼亚理工大学的古生物学家肖树华博士（Shuhai Xiao，音译，生物谷注），其早年毕业于北京大学，后于哈佛大学获得博士学位，现任弗吉尼亚理工大学地球科学系副教授。
地球上最大一次物种分裂发生于5亿4200万年前，被称作寒武纪生命大爆炸。但是在这篇文章中，研究人员认为，一个和它相似的，迅速的进化爆炸在其爆炸的3300万年前发生，他们将这次事件成为阿瓦隆爆炸。肖博士表示：“现在看来从575年至5亿2000万年前肉眼可见的生命体，经历不止一次，而至少是两次巨大的突发形态扩张。”
研究人员分析研究了6亿3500年到5亿4200年前的震旦纪期间的生命体，并比较了200种不同的物种以揭示他们的体型--以及丰富的多样性--在同期出现。他们发现，尽管在生物多样性上有了首次推进，但是震旦纪的所有生物都在随之而来的寒武纪爆炸前全部消失。“阿瓦隆爆炸代表了一个独立的，和寒武纪爆炸相似的进化模式失败的试验。”
生物谷推荐原始出处：
Science 4 January 2008:
Vol. 319. no. 5859, pp. 81 - 84
DOI: 10.1126/science.1150279
The Avalon Explosion: Evolution of Ediacara Morphospace
Bing Shen, Lin Dong, Shuhai Xiao,* Micha Kowalewski
Ediacara fossils [575 to 542 million years ago (Ma)] represent Earth's oldest known complex macroscopic life forms, but their morphological history is poorly understood. A comprehensive quantitative analysis of these fossils indicates that the oldest Ediacara assemblage—the Avalon assemblage (575 to 565 Ma)—already encompassed the full range of Ediacara morphospace. A comparable morphospace range was occupied by the subsequent White Sea (560 to 550 Ma) and Nama (550 to 542 Ma) assemblages, although it was populated differently. In contrast, taxonomic richness increased in the White Sea assemblage and declined in the Nama assemblage. These diversity changes, occurring while morphospace range remained relatively constant, led to inverse shifts in morphological variance. The Avalon morphospace expansion mirrors the Cambrian explosion, and both events may reflect similar underlying mechanisms.
Department of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA.
* To whom correspondence should be addressed. E-mail: xiao@vt.edu
附：
Shuhai Xiao
Associate Professor of Geobiology
Department of Geosciences, Virginia Tech
Blacksburg, VA 24061, USA
Biography:
Associate Professor: Virginia Tech, 2005-;
Assistant Professor: Virginia Tech, 2003-2005;
Assistant Professor: Tulane University, 2000-2003;
Postdoctoral Fellow: Harvard University, 1998-2000;
Research Assistant: Nanjing Institute of Geology and Paleontology, 1991-1993;
PhD: Harvard University, 1998;
AM: Harvard University, 1996;
MSc: Beijing University, 1991;
BSc: Beijing University, 1988;
Research:
Focuses: Precambrian Geobiology; Early Animal History; Proterozoic Algal Fossils; Lagerst䴴en; Taphonomy;
Other Interests: Carbonates; Isotopes; Fossil Record of Microbes;
The Doushantuo project
In the past several years, Xiao and his colleagues have been focusing on the Neoproterozoic Doushantuo Formation (ca. 550-630 million years old) in South China. The Doushantuo Formation contains multiple taphonomic windows. Extraordinary fossils such as animal embryos and multicellular algae are preserved in Doushantuo phosphorites and cherts. Macroscopic algal fossils occur in Doushantuo shales. Together these taphonomic windows give a clearer and more complete picture of the Neoproterozoic biosphere and provides insights into preservational biases of the Neoproterozoic fossil record. Reliable reconstruction of the temporal and spatial distribution of Neoproterozoic biodiversity is critical to the understanding of the interactions between Neoproterozoic climate change and biological evolution.
