Abstract

A chain of pellets (Neonereites uniserialis), usually attributed to a coelomate or pseudocoelomate metazoan, is described from the middle Dalradian 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 deformation plus intrusion by granites at Ben Vuirich dated at 597 ±11 and 590 ± 2 Ma. U-Pb zircon chronology for early metazoan evolution suggests that this is the earliest putative evidence for coelomates or pseudocoelomate discovered so far, with a minimum ‘interglacial’ age of c. 600 Ma bp. It is from about this time that a fall takes place in the maximum δ¹³C 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 Neoproterozoic to Cambrian interval.