We also constructed a time-scale evolutionary tree of the RdRp gene (Figure 2B). The tree shows that the MRCA of RdRp of the present GII.2 strains was in the year 1696 (mean ± 95% HPD: 1542–1837). The common ancestor of the GII.P16-GII.2 strains diverged in 1858 (mean ± 95% HPD: 1747–1950) and formed two clusters. Moreover, the GII.P16-GII.2 strains detected in 2010–2012 diverged at 1989 (mean ± 95% HPD: 1972–2003), whereas the GII.P16-GII.2 strains detected in 2009–2010 and 2012–2014 diverged at 1986 (mean ± 95% HPD: 1968–2002). The common ancestor of the GII.P2-GII.2, GII.P12-GII.2, and GII.Pe-GII.2 diverged in 1828 (mean ± 95% HPD: 1741–1913). The RdRp gene of GII.P2-GII.2 diverged in 1992 (mean ± 95% HPD: 1984–2000). The evolutionary rate of these RdRp genes was 1.314 × 10−3 substitutions/site/year (mean ± 95% HPD: 0.698–1.95 × 10−3 substitutions/site/year).