The Burgess Shale Biota

摘要

In the early Cambrian, the metazoans underwent a major taxonomic and adaptive radiation. In the Phanerozoic, biotic radiations when a particular group develop the ability to live in a new habitat from which they had previously been excluded (adaptive radiation: for example, in the early Jurassic one group of sea urchins developed the ability to live burrowing within the sediment) or (2) when a group expanded into ecological space which had been made vacant by the demise of rival organisms (for example, the radiation of the mammal in the Cenozoic following the demise of the dinosaurs at the end of the Cretaceous).The radiation of the metazoans in the early Cambrian apparently involved both the development of new adaptations for the exploitation of the environment and expansion into habitats which were previously unexploited. These adaptations involved two events which were novel in the history of life, namely broad diversification at the level of phyla and the evolution of a mineralized or chitinous skeleton in a broad range of organisms.