Figure 1.

Provisional time scale for events around the Precambrian–Cambrian boundary. 1, range of large, acanthomorphic ‘Ediacaran’ acritarchs (a genus that contains metazoan-like embryos is found from close to the bottom of their range just above the Marinoan glaciation rocks); 2, possible range of the Doushantuo embryos and cnidarian-like fossils according to Barfod et al. (2002); 3, possible range of the same according to Condon et al. (2005) (which is correct is uncertain, but the former is favoured here); 4, the ‘Ediacaran’ biota; 5, trace fossils; 6, Cloudina and Namacalathus; 7, classical small shell fossils; 8, trilobites. The alphabets correspond to the key dated points in metazoan evolution in Peterson & Butterfield (2005) based on minimum evolution: A, origin of crown-group Metazoa; B, total-group Eumetazoa; C, crown-group Eumetazoa; D, crown-group bilateria (here equivalent to Protostomia+Deuterostomia); E, crown-group Protostomia. The ‘formative interval’ during which distinctive bilaterian features were assembled according to this dating is marked by arrows.