Tree topology and the models used for the likelihood-ratio tests. The numbers on the tree branches represent the mean number of substitutions per codon along the branch as estimated by the program Mega4. Branches B (common ancestor of birds) and Gl (common ancestor of Galliformes) were the lineages of the analysis in free branch models.
Yaklichkin et al. BMC Evolutionary Biology 2011 11:302 doi:10.1186/1471-2148-11-302