 These fossils have been preserved in a distinctive style known as Burgess shale type preservation , which preserves fairly tough tissues such as cuticle as thin films , and soft tissues as solid shapes , quickly enough that decay has not destroyed them . Moderately soft tissues , such as muscles , are lost . Scientists are still unsure about the processes that created these fossils . While there is little doubt that the animals were buried under catastrophic flows of sediment , it is uncertain whether they were transported by the flows from other locations , or lived in the area where they were buried , or were a mixture of local and transported specimens . This issue is closely related to whether conditions around the burial sites were anoxic or had a moderate supply of oxygen . <unk> conditions are generally thought the most favourable for fossilization , but imply that the animals could not have lived where they were buried . 
