Dynamical evolution of regular Jupiter and Saturn in the JSREG and JSCHA simulations. In both cases the planets are in 2:1 MMR (the critical angle ﹩{\phi }_{2}=2{\lambda }_{\mathrm{Sat}}-{\lambda }_{\mathrm{Jup}}-{\varpi }_{\mathrm{Jup}}﹩ associated with the 2:1 MMR librate around zero degree while the ﹩{\phi }_{1}=2{\lambda }_{\mathrm{Sat}}-{\lambda }_{\mathrm{Jup}}-{\varpi }_{\mathrm{Sat}}﹩ circulates). ﹩{\lambda }_{\mathrm{Sat}}﹩ and ﹩{\varpi }_{\mathrm{Sat}}﹩ are Saturn’s mean longitude and longitude of pericenter. ﹩{\lambda }_{\mathrm{Jup}}﹩ and ﹩{\varpi }_{\mathrm{Jup}}﹩ are Jupiter’s mean longitude and longitude of pericenter. The initial conditions of these two simulations are provided in the Appendix.