Post-mortem transport and population longevity recorded in scolecodont death assamblages

Scolecodonts (worm jaws) are common microfossils in many Paleozoic deposits. To evaluate what information might exist in that fossil record, life and death assemblages of scolecodonts were sampled in one intertidal embayment. The lightly mineralized scolecodonts of Eunicidae polychaetes were rare but jaws of Nereidae polychaetes were often abundant in the sediments. Sands stabilized by the tubes of benthic infauna and the seagrass Zostera marina appear to yield in situ preservation; losses by dissolution and/or post-mortem transport seem appreciable for Platynereis bicanaliculata. In contrast, scolecodonts of Nereis brandti apparently accumulate over several years; these heavily mineralized jaws were more numerous than the live populations at each of four study sites. Size distributions of jaws of these two nereids are consistent with patterns of predation by the nemertean Paranemertes peregrina, but the patterns are confounded in sheltered sites, probably as a result of post-mortem transport, by numerous small fragments. Scolecodonts become exposed to currents when Paranemertes defecates on the sediment surface; these can be transported by relatively weak currents. Only the most durable jaws appear to accumulate as fragments at sheltered sites high in the intertidal zone.