Early animal evolution has often been seen as a rapid radi-ation of the metazoan phyla during the Early Cambrian (from542Ma; often called the ‘‘Cambrian explosion’’). Only veryfew fossils obviously belonging to living phyla or their stemgroups have been described from the Late Precambrian strata(Ediacaran; 632–542Ma), although the diversity of phyla mayhave been greater than it seems, because the bodies of theseanimals did not contain the hard parts characteristic of theirextant relatives. However, both molecular phylogenies(Peterson et al. 2008) and the record of organic compoundscharacteristic of siliceous sponges from the Cryogenian (713–635Ma; Love et al. 2009), indicate a much earlier origin of themulticellular animals (about 770–750Ma; Fig. 1). Whateverthe timescale, how did the evolution from the earliest animals(sponges) to the 30 or so bilaterian phyla proceed?The ‘‘Cambrian explosion’’ is now thought by many evo-lutionary biologists to comprise two phases: (i) cladogenesis inthe Precambrian (Parker 2003; Peterson et al. 2008); and then(ii) hard-part evolution (leading to more dynamic lifestylesand ecology) in the Early Cambrian (Fortey et al. 1996;Parker 2003). Both molecular (Peterson et al. 2008) and mor-phology-based (Nielsen 2008) phylogenies indicate a ratherslow stepwise radiation of the three sponge ‘‘phyla’’ (i.e., thethree major clades within the old ‘‘Porifera’’) and the cnid-arians leading to the origin of the bilaterians about 650Ma(Fig. 1). During the Ediacaran, a more rapid cladogenesisgave rise to the approximately 30 bilaterian phyla or theirstem groups. This evolutionary pattern has often been pos-tulated to be the result of environmental changes. However,the importance of morphological innovation has also beenemphasized (Marshall 2006).The organisms of the sponge grade are all microphages,which filter small particles from the water with theirchoanocytes and digest them intracellularly. There are onlysmall morphological differences between the three sponge‘‘phyla’’ (Nielsen 2008).Cnidarians and bilaterians (together called Neuralia (Niel-sen 2008)), share many advanced characters, such as a gut, anervous system, and muscle cells. These new organ systemsenable the ingestion of larger food organisms and extracel-lular digestion in the gut. However, the cnidarians lack abrain; and their radial or quasi-bilateral body form, with asac-shaped gut, apparently restricts their life-style to pelagicor sessile (Ruppert et al. 2004). Cnidarians are generally pas-sive predators, which paralyze and ingest prey that gets intocontact with the nematocysts on their tentacles. The onlyother common feeding method is collection of particles, whichget into contact with epithelia and become transported to themouth by cilia, in some cases captured in mucus. None of thespecies are active hunters or deposit feeders.Bilaterians, on the other hand, show a whole series ofcoupled morphological novelties, the most conspicuous beingthe bilateral symmetry with anterior mouth and brain, atubular gut and a posterior anus. On the genetic level, thelong Hox-cluster, which is engaged in patterning along theanterior–posterior axis, appears to be intimately coupled withthis body plan (Chiori et al. 2009). The evolution of the bila-terian body plan in the Late Cryogenian or Early Ediacaranlikely opened a whole new world of possible life-styles andfeeding strategies in hitherto unoccupied ecospace (Xiao andLaflamme 2008). Today, many bilaterian species are huntersor scavengers. Others are deposit feeders (selective or nonse-lective), which are able to process larger amounts of bottommaterial in a long gut with different functional regions. Allthese feeding methods depend, in one way or another, on thebrain, which can coordinate sensory input and behavior inresponse to larger food items, and on the through gut, whichcan digest larger amounts of material.Although the genetic evidence suggests the existence of anEdiacaran fauna comprising stem groups of all the phyla seenin Cambrian deposits, the Late Precambrian fossil record ofearly bilaterians is very poor. Very few body fossils, such asthe putative mollusc Kimberella, are known. Indeed, the sev-eral different types of fossil trails from the Late Precambrianindicate that most organisms were small ciliary gliders (Weberet al. 2007) which have left no body fossils.In stark contrast, the earliest Cambrian fauna FCheng-jiang (Hou et al. 2004)Fis remarkably rich in representatives