Lysine-containing CTD repeats first appeared in Metazoa and increased in prevalence in the ancestor of Deuterostomia. Phylogenetic tree of eukaryotic species considered in our analysis organized by approximate divergence estimates. For each species, the number of RPB1 CTD repeats and lysine-containing repeats are given. Ancestral counts were inferred for each internal node of the tree using symmetric Wagner parsimony. The number of CTD heptad repeats increased substantially in the ancestor of all Metazoa (31 to 44 repeats). This was accompanied by the appearance of repeats with lysine at position seven (K7) in ancestral Metazoa and an increase in K7 repeats in Deuterostomia (from 3 to 7 repeats).