To understand the phylogenetic relationship of IFITM gene family, 160 functional IFITM genes identified from 27 vertebrate species (Table S1 ) were subjected to phylogenetic analyses using Bayesian inference, maximum likelihood (ML) and maximum parsimony (MP) methods. The Bayesian, ML and MP trees show consistent topological structures (Figs. 2A and S1). All functional IFITM genes were well divided into three clades I, II and III with Bayesian posterior probabilities of $97. These analyses indicate that the IFITM family most likely originated from three progenitors.