The timing of the metazoan radiation according to the molecular clock. The phylogenetic tree for 41 metazoan taxa rooted on the yeast Saccharomyces cerevisiae as determined by Bayesian phylogenetic analysis (see text) is shown. The deuterostomes are shown in red, spiralian protostomes in green, ecdysozoan protostomes in blue, cnidarians in orange, the homoscleromorph Oscarella in salmon pink, calcisponges in purple and demosponges in magenta. The nodes of the tree are positioned according to the optimum as determined from the Bayesian autocorrelated method of Thorne et al. (1998), as implemented in the software package ‘Multidivtime’ (Thorne & Kishino 2002) using a root prior of 1000 Myr ago (s.d.=500 Myr ago). The 95% HPD credibility intervals are shown in brackets. The red crosses are the estimates for clades with internal calibration points as determined by Bayesian algorithm Beast (Drummond et al. 2006) using uniform priors and an exponential rate distribution; black Xs are the estimates using exponential priors and the same rate distribution. Note that much of the metazoan diversification occurs during the Ediacaran (brown), which lies between the Cryogenian (ice blue) and the Cambrian (green).

Putative Ediacaran metazoans. (a) Natural cast on bed base of Kimberella resting trace (asterisk) and Radulichnus radular feeding trace fans (arrows); scale bar, 1 cm. (b)Parvancorina minchami; scale bar, 1 cm. (c) Spriggina floundersi; scale bar, 10 mm. (d) Marywadea ovata; scale bar, 10 mm. (e) Dickinsonia costata; scale bar, 2 cm.