Evolutionary scenarios for FGF evolution in eumetazoans. The minimal gene content of each eumetazoan lineage (chordates, ambulacrarians, nematodes, arthropods, annelids, mollusks, and cnidarians) is mentioned in the center (grey box). Two evolutionary hypotheses are proposed: on the left side (hypothesis 1), starting from a minimum gene set of two genes (green box) in the eumetazoan ancestor, diversity of the subfamily is acquired through chordate-specific duplications; on the right side (hypothesis 2), diversity of the subfamily was acquired very early in metazoan evolution, with 8 subfamilies in the eumetazoan ancestor (red box) and then numerous gene losses in the different lineages occurred. Gene losses are represented by triangles. E: eumetazoan ancestor; P: protostome ancestor; D: deuterostome ancestor and B: Bilaterian ancestor.
