About four hundred million years ago earthquake activity and possibly major storms caused sudden movements of large quantities of muddy sediment along the seafloor. Animal communities in the path of these sediment-laden flows were instantly engulfed, the inhabitants "frozen" in the last moment of their lives. Amazingly, many of the creatures lost in this ancient catastrophe were almost perfectly preserved through the eons, fossilized in a thick series of muds now known as the Hunsruck Slate west of the Rhine Valley in western Germany. Excavations there have yielded the most diverse and...