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BENGTSON—ORIGINS AND EARLY EVOLUTION OF PREDATIONFIGURE 1—Time diagram showing diversities of stromatolites (after Awramik and Sprinkle, 1999) andacritarchs (after Knoll, 1994b), with timings of the predation-related evolutionary steps discussed in thetext (knife tip points to the first appearance of macrophagous predators in the fossil record; othersymbols show only approximate timings). Snowflakes indicate periods of global glaciations (“SnowballEarth”; Kirschvink, 1992, 2000; Hoffman et al., 1998).protists (Allison, 1981; Allison and Hilgert, 1986;Kaufman et al., 1992).THE ROLE OF PREDATION INTHE CAMBRIAN EXPLOSIONFollowing the massive glaciations in the lateNeoproterozoic (Kirschvink, 1992; Hoffman et al.,1998; Eerola, 2001), the biosphere underwent athorough restructuring. On the face of it, it was aburgeoning of multicellular life, but it has becomeclear that the event affected the biosphere at alllevels, and also that the biological events werecoupled with geochemical, oceanographic,tectonic, and atmospheric changes. The end resultwas that a modern type of marine biosphere, withcomplex food webs and diverse feeding strategies,was established for the first time. In thesedimentary record, it is expressed as profounddifferences between rocks below and above thetransitional interval. This “Cambrian explosion,”which culminated between 550 and 540 Ma, hasbeen and is the focus of intense and multifacetedresearch and speculation (recent reviews of the fieldare by Fortey et al., 1996; Butterfield, 1997; Vidaland Moczydlowska-Vidal, 1997; Knoll and Carroll,1999; Valentine et al., 1999; Brasier, 2000; Buddand Jensen, 2000; Conway Morris, 2000; Levinton,2001, p. 443–494; Zhuravlev, 2001). A recentthematic volume (Zhuravlev and Riding, 2001)deals specifically with the ecological aspects of theCambrian explosion.The Cambrian explosion is, in its anatomy,thoroughly dependent on ecological processes. Thatpredation had an important role might seem obvious;and already in the beginning of the last century theproposal was made that the sudden appearance ofskeletal tissues in the Cambrian was due to theintroduction of predators (Evans, 1912). At that time,the common understanding regarding thePrecambrian biota was “not that animals did not existin those early periods of the earth’s history, but thatthe scarcity of creatures having a resistant skeleton,precluded the preservation of their remains in sucha form as to be easily recognizable” (Matthew,1912). Interestingly, after Cloud (1948, 1968a)successfully argued for the opposite alternative, thatthe metazoans did not have a long Precambrianhistory and that the Cambrian explosion was notjust a calcareous dress-up party, the role of Cambrianpredators began to be downplayed. Evans’ idea aboutthe crucial influence of predators for the origin ofskeletons had lived on (Dunbar, 1960; Hutchinson,1961), but when Cloud’s interpretation de-299