Molecular clock analysis
To estimate the divergence time among these 11 species, all of the 4d
sites were extracted from the super sequences using in-house Perl
scripts. The divergence times were analyzed by Markov chain Monte Carlo
sampling with samples drawn every 2,000 steps and 100,000 samples, and
the results were calibrated by the fossil records downloaded from the
TIMEtree database (http://www.timetree.org).