Many conodont lineages that appear in the Ludlovian on Gotland and elsewhere have no known earlier record anywhere. The closest relatives are found not in the earliest Ludlovian but in the latest Llandoverian-earliest Wenlockian or in still older beds. Ordinary biofacies and lithofacies models fail to explain the observed distribution, since such lineages appear in all of the different facies identified. Either these lineages evolved in an as yet unsampled province, the isolation of which broke down gradually during the Ludlovian, or their appearance reflects changes in the chemistry of the seawater. If the latter interpretation applies, then it indicates...