English geologist and palaeontologist William Buckland (1784–1856) realised that a dramatic change in the fossil record occurred around the start of the Cambrian period, 542 million years ago.[68] The earliest Cambrian trilobite fossils are about 530 million years old, but were already both diverse and widespread, suggesting that the group had a long, hidden history.[69] The earliest fossils widely accepted as echinoderms appeared at about the same time[70] Because Darwin's contemporaries had insufficient information to establish relative dates of Cambrian rocks, they had the impression that animals appeared instantaneously.