Positive time-dependent phylogenies were simulated using a time-dependent process (b(t)=0.01eαt) for α = 0.001, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, and 1, with branch lengths restricted to the distribution of branch lengths from one downsampled SARS-CoV-2 phylogeny.