In general, the uncorrelated model yielded substantially wider Cr Is, sometimes with ranges of hundreds of millions of years (e.g., Calcarea, Demospongiae).Under both models however, Metazoa and its deepest subclades – Porifera, Epitheliozoa (Placozoa Eumetazoa), Eumetazoa (Coelenterata [=Cnidaria Ctenophora] Bilateria), and total-group Bilateria – as well as the crown-groups of Coelenterata, Cnidaria, Porifera, Silicea (siliceous sponges), and Calcarea homoscleromorph sponges were estimated to have arisen before the Sturtian glaciation (the first of the Neoproterozoic Snowball Earth episodes). Dotted line indicates Precambrian/Cambrian boundary. Gray areas indicate Sturtian (left) and Marinoan (right) glaciations For the deepest nodes (Opisthokonta to Eumetazoa), all three calibration sets resulted in pre-Sturtian age estimates, with C yielding the oldest, A the youngest, and B intermediate estimates (Fig. The same pattern was also obtained for the crown groups of Coelenterata, Cnidaria, Porifera, and Calcarea Homoscleromorpha.
This dataset includes all non-bilaterian phyla and classes, a selected sample of representatives from all three bilaterian supergroups (Deuterostomia, Ecdysozoa, Lophotrochozoa), as well as a suite of non-metazoan opisthokonts as outgroups.
Supporting a well-resolved phylogeny, this dataset appears well suited for investigating the timing of deep metazoan phylogeny.
Relaxed molecular-clock methods provide an alternative means of estimating the timing of cladogenesis deep in the metazoan tree of life.
So far, thorough molecular clock studies focusing specifically on Metazoa as a whole have been based on relatively small datasets or incomplete representation of the main non-bilaterian lineages (such as sponges and ctenophores), which are fundamental for understanding early metazoan evolution.
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However, they did not include Ctenophora and only sampled three of the four classes of Porifera (Hexactinellida was excluded).