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).