Dzik, J. 2007. The Verdun Syndrome: Simultaneous origin of protective armor and infaunal shelters at the Precambrian-Cambrian transition. In: P. Vickers-Rich & P. Komarower (eds) The Rise and Fall of the Ediacaran Biota. Geological Society, London, Special Publications 286, 405-414. 

Abstract: All of the structurally identifiable latest Ediacaran and earliest Cambrian infaunal trace fossils represent shelters of animals feeding above the sediment surface. It is the case with the most complete and oldest radiometrically dated Precambrian-Cambrian transition strata along the Khorbusuonka River in northern Siberia, in the basal Cambrian succession at Meishucun in southern China, richest in small shelly fossils, as well as in the type succession of the Vendian in Podolia, Ukraine. The oldest traces of feeding within the mud are known from no earlier than the late Tommotian of Siberia, Mongolia, Sweden, and Poland. This suggests that the invention of hydraulic mechanisms of sediment penetration was enforced by predation, not by trophic needs. Various ways to protect the body by secretion of a mineral skeleton or building tubes by collected mineral grains were developed by other animals at the same time. Predation may thus appear to be the triggering mechanism for the "Cambrian explosion." Subsequent increase in the depth of bioturbation resulted in a profound change of taphonomic conditions, artificially enhancing the effects of evolution.