Dense concentrations of Skolithos, commonly called piperock, exemplify the characteristic ichnofabric of the Skolithos ichnofacies in Paleozoic strata. Piperock occurs in sandstones and coarse siltstones within all types of shallow marine facies and is not restricted to beach, littoral or intertidal sediments. Piperock, however, is restricted to terrigenous clastic sediments. An analysis of the temporal distribution of piperock confirms the previous observations that piperock is typical of the Cambrian but also demonstrates that piperock occurs throughout the Paleozoic, decreasing in abundance after the Cambrian. This distribution may be a result of large-scale physical or biological factors. Preserved nearshore sandstones may decrease through this time interval. In addition, the decline of piperock corresponds with the Ordovician faunal diversification when bioturbation increases in other environments and, thus, may reflect the appearance of new and better adapted fauna in the nearshore terrigenous clastic setting.