Nice article from Scientific American on Travel and Trilobites:
.... Still today the Silurian (some 443,7-416 milion years ago) is one of the most enigmatic epochs in the history of earth; marked by glaciations at the beginning, it was at the end of this period that the landmasses, until then barren deserts, became colonized by plants and animals. The sea was already populated by a rich assemblage of trilobites, brachiopods, crinoids and other strange invertebrates....
