The linearized NJ tree was used to convert evolutionary distances to the relative molecular time scale. A GABAB-like receptor from Dictyostelium discoideum (slime mold), GrlJ, was used as an outgroup to root the tree. Bootstrap values of more than 70% are presented on the node. T1, T2 and T3 indicate time points of the first, second and third gene duplication events respectively. According to the global clock, we estimate T1 = 899 Mya, T2 = 638 Mya and T3 = 565–573 Mya. The split time of Dictyostelium discoideum (1085 Mya) was used to calibrate the timescale.