Evolutionary Exploitation of Design Options by the First Animals with Hard Skeletons

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Science  19 May 2000:
Vol. 288, Issue 5469, pp. 1239-1242
DOI: 10.1126/science.288.5469.1239

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The set of viable design elements available for animals to use in building skeletons has been fully exploited. Analysis of animal skeletons in relation to the multivariate, theoretical “Skeleton Space” has shown that a large proportion of these options are used in each phylum. Here, we show that structural elements deployed in the skeletons of Burgess Shale animals (Middle Cambrian) incorporate 146 of 182 character pairs defined in this morphospace. Within 15 million years of the appearance of crown groups of phyla with substantial hard parts, at least 80 percent of skeletal design elements recognized among living and extinct marine metazoans were exploited.

  • * To whom correspondence should be addressed. E-mail: r_thomas{at}

  • Present address: Department of Organismal Biology and Anatomy, University of Chicago, 1027 East 57 Street, Chicago, IL 60637, USA.

  • Present address: Rose Center for Earth and Space, American Museum of Natural History, 200 Central Park West, New York, NY 10024, USA.

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