To determine if all genotypes exhibited the same population history observed for the composite genotype data set, we repeated the analysis based on 97 dated full length F genes, which provided a larger data set for this analysis. Isolates from genotype III, IV, and V were not included because limited numbers of dated sequences were available. The TMRCA for genotype II was estimated to be 1899620 years, and the estimated evolutionary rates were between 0.3-1.1610 24 substitutions/site/year, making this the slowest evolving aPMV-1 genotype ( Table 2 ). Genotype I and VI emerged in the early 1960's and had higher evolutionary rates than genotype II. The most recently emerged strain was genotype VII, which dates to the late 1970's and had the highest evolutionary rate. BSP analyses based on the F gene demonstrated that each genotype had a unique population history. Prior to the emergence of genotype VII in the 1970s (phase i), genotype II showed an increase in population size ( Figure 5B ). After the emergence of genotype VII (phase ii) the population size of genotype VI began to increase, while that of genotypes I and VII were relatively constant. Phase iii depicts the time of the population bottleneck observed in Figure 5A , which was based on all genes in the composite genotype data set. Only genotypes I and VI show a trend for decreasing population size during this time. The last decade has been the most dynamical for the four genotypes of aPMV-1 (phase iv; Figure 5B ). Genotypes I and VII showed a marginal increase in effective population size followed by a decline; genotype I has continued to decline, whereas genotype VII appears to have stabilized. Genotype VI showed continuous decline in population size in phase iv ( Figure 5B ). Although estimates of population sizes for genotypes I, VI, and VII, have some degree of overlaps at the 95% posterior limit, genotype II shows no sign of reduction in effective population size since its origin ( Figure 5B ).