Department of Earth Sciences, University of California, Riverside, California 92521.
Integr Comp Biol. 2003 Feb;43(1):178-84. doi: 10.1093/icb/43.1.178.
There was a major diversification known as the Ordovician Radiation, in the period immediately following the Cambrian. This event is unique in taxonomic, ecologic and biogeographic aspects.While all of the phyla but one were established during the Cambrian explosion, taxonomic increases during the Ordovician were manifest at lower taxonomic levels although ordinal level diversity doubled. Marine family diversity tripled and within clade diversity increases occurred at the genus and species levels. The Ordovician radiation established the Paleozoic Evolutionary Fauna; those taxa which dominated the marine realm for the next 250 million years. Community structure dramatically increased in complexity. New communities were established and there were fundamental shifts in dominance and abundance.Over the past ten years, there has been an effort to examine this radiation at different scales. In comparison with the Cambrian explosion which appears to be more globally mediated, local and regional studies of Ordovician faunas reveal sharp transitions with timing and magnitudes that vary geographically. These transitions suggest a more episodic and complex history than that revealed through synoptic global studies alone.Despite its apparent uniqueness, we cannot exclude the possibility that the Ordovician radiation was an extension of Cambrian diversity dynamics. That is, the Ordovician radiation may have been an event independent of the Cambrian radiation and thus requiring a different set of explanations, or it may have been the inevitable follow-up to the Cambrian radiation. Future studies should focus on resolving this issue.
紧接着寒武纪之后的奥陶纪，发生了一次主要的生物多样性分化，被称为奥陶纪辐射。此次事件在分类学、生态学和生物地理学方面都独具特色。虽然除了一门外，所有的门在寒武纪大爆发期间就已建立，但在奥陶纪，分类学的增加体现在较低的分类学水平上，尽管科级的多样性增加了一倍。海洋科的多样性增加了两倍，在属和种的水平上，内部进化枝的多样性也有所增加。奥陶纪辐射确立了古生代进化动物群；这些生物在接下来的 2.5 亿年里主宰了海洋领域。群落结构的复杂性急剧增加。新的群落建立起来，优势和丰度发生了根本的转变。在过去的十年里，人们一直试图从不同的角度来研究这种辐射。与似乎更具有全球性影响的寒武纪大爆发相比，奥陶纪动物群的局部和区域研究揭示了具有时间和地域差异的急剧转变。这些转变表明，与仅通过全球综合研究揭示的情况相比，奥陶纪的历史更具阶段性和复杂性。尽管奥陶纪辐射具有明显的独特性，但我们不能排除它是寒武纪生物多样性动态的延伸的可能性。也就是说，奥陶纪辐射可能是一个独立于寒武纪辐射的事件，因此需要一套不同的解释，或者它可能是寒武纪辐射的必然后续。未来的研究应集中于解决这一问题。
