Evolutionary exploitation of design options by the first animals with hardskeletons

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