In each clade, eutherian IFITM genes form a separate group from opossum and bird genes, consistent with the species phylogeny. Besides IFITM5 and IFITM10, IR-IFITM genes also have orthologs in both marsupials and eutherians, arguing against previous observation that only IFITM5 and IFITM10 orthologs could be identified in marsupials and eutherians [30] . In addition, clade II and III contain homologous IFITM sequences from teleosts and amphibians, but clade I does not ( Fig. 2A) , indicating that IR-IFITM originated later than IFITM5 and IFITM10.