NEONEREITES-UNISERIALIS FROM C.600-MA YEAR-OLD ROCKS IN WESTERN SCOTLAND AND THE EMERGENCE OF ANIMALS

A chain of pellets (Neonereites uniserialis), usually attributed to a coelomate or pseudocoelomate metazoan, is described from the middle Da lradian Bonahaven Formation of western Scotland, in sandstones not far above the Port Askaig Tillite. This trail lies more than 8 km below U -Pb zircon-dated Tayvallich lavas (595 +/- 4 Ma) and predates early de formation plus intrusion by granites at Ben Vuirich dated at 597 +/- 1 1 and 590 +/- 2 Ma. U-Pb zircon chronology for early metazoan evolutio n suggests that this is the earliest putative evidence for coelomates or pseudocoelomate discovered so far: with a minimum interglacial' age of c. 600 Ma sp. It is from about this time that a fall takes place i n the maximum delta(13)C of carbonates, suggestive of a decline in the long term rate of carbon burial. One explanation for this decline is the increasing impact of metazoan bioturbation through the late Neopro terozoic to Cambrian interval.