Divergence time estimates for the early history of animal phyla and the origin of plants, animals and fungi

In the past, molecular clocks have been used to estimate divergence times a mong animal phyla, but those time estimates have varied widely (1200-670 mi llion years ago, Ma). In order to obtain time estimates that are more robus t, we have analysed a larger number of genes for divergences among three we ll-represented animal phyla, and among plants, animals and fungi. The time estimate for the chordate-arthropod divergence, using 50 genes, is 993 +/- 46 Ma. Nematodes were found to have diverged from the lineage leading to ar thropods and chordates at 1177 +/- 79 Ma. Phylogenetic analyses also show t hat a basal position of nematodes has strong support (p>99%) and is not the result of rate biases. The three-way split (relationships unresolved) of p lants, animals and fungi was estimated at 1576 +/- 88 Ma. By inference, the basal animal phyla (Porifera, Cnidaria, Ctenophora) diverged between about 1200-1500 Ma. This suggests that at least six animal phyla originated deep in the Precambrian, more than 400 million years earlier than their first a ppearance in the fossil record.