Phylogenetic tree from analysis of CDK family proteins in Homo sapiens , Nematostella vectensis , Thecamonas adhaerens , Amphimedon queenslandica , Monosiga brevicollis , and Salpingoeca rosetta . Maximum likelihood (ML) and Bayesian analyses were conducted using RAxML and PHYLOBAYES 3.3, respectively. Both methods produced trees with nearly identical topologies. The first numbers above branches indicate Bayesian posterior probabilities (only key branches are labeled), and the second numbers above branches indicate ML bootstrap percentages. The scale bar shows the number of substitutions per site. Sequences of Hsa-GSK3alpha, Hsa-MAK, and Hsa-HCDKL1 were used as outgroups. All proteins are labeled with species names followed by accession numbers. Species abbreviations are as follows: Hsa, H. sapiens; Nve, N. vectensis; Tad, T. adhaerens; Aqe, A. queenslandica; Mbr, M. brevicollis. The alignment used for this analysis is found in Additional file 1: File S1.