are one of the best examples of the difference between phylogeny and taxonomy: how fish are organized by physical characteristics, while phylogeny is how fish are organized by family relationships. The bearing of live young in this family has arisen more than once, while at least one egg laying member of the same family (Genus Cynopoecilus) practices internal fertilization yet lacks the godopodium, the modified anal fin, of male livebearers. Perhaps in some number million years they will evolve one.
But the point is "The Livebearers" used to be a category all by themselves in the fish tree of life once, but now they're tucked away in a division of the killifish and to further complicate things there are egg laying Poeciliids (The "Lampeyes") as well as these, the live bearing fishes in the Poeciliidae.
