EXCEPTIONAL PRESERVATION IN THE ORDOVICIAN – CONTRASTING SETTINGS REVIEWED

Environmental conditions during the Cambrian favored the fossilization of soft-bodied organisms, particularly in Burgess Shale-type preservations. Soft-bodied organisms are less well represented during the ~42 million years of the Ordovician but this situation is being remedied by new discoveries. Exceptional preservation occurs where suitable facies and conditions are present. The early Ordovician Fezouata formations of Morocco yield a diverse Burgess Shale-type fauna representing a normal marine setting which casts important light on the early stages of the Great Ordovician Biodiversification Event. Other exceptionally preserved Ordovician faunas are much less diverse and represent more unusual environments. The middle Ordovician Winnishiek Lagerstätte of Iowa is preserved in an impact crater, and the late Ordovician Beecher's Trilobite Bed near Rome, New York, represents an iron-dominated low oxygen deeper water setting. (Other important late Ordovician examples include the cold water Soom Shale in South Africa and faunas from Manitoba in Canada.) Silurian exceptional preservations are no more abundant, but the fully marine Herefordshire biota in the Wenlock of England, preserved in concretions in volcanic ash, is remarkable. Such Konservat-Lagerstätten continue to yield new discoveries that underpin our understanding of the phylogeny and Paleozoic history of marine animals.