Alternative scenarios for phylogenetic relationships between gnathostome Bmp2/4/16 and their lamprey homologs. (A) The consensus tree of the eight topologies supported by our ML analysis (see Table 2 for details). Under this scenario, gene duplications that gave rise to Bmp2, -4, and -16 are postulated before the cyclostome-gnathostome split. This scenario also assumes additional gene duplications and losses. (B) The scenario where the cyclostome-gnathostome split occurred before the gene duplications that gave rise to three lamprey subtypes and also before gene duplications that gave rise to gnathostome Bmp2, -4 and -16. (C) The scenario where gene duplications that gave rise to Bmp2, -4, and -16 preceded the cyclostome-gnathostome split.