It has often been suggested that this type of preservation was possible only when sediments were not disturbed by burrowing animals or the anchors of plants. However a similar type of preservation has been found in fossils from the Late Riphean period, about 850 to 750 million years ago, but in no known fossils between the end of that epoch and the start of the Cambrian. This suggests that such bioturbation has little to do with the appearance and disappearance of Burgess Shale type preservation.