Later still, a third gene duplication event occurs and we get sperm with the haploid number of 16. But remember, we no longer buy the ladder icon. Tetrapods, including birds and mammals, evolved from the early gnathostome fish without another gene duplication event occurring. By the hypothesis, minnows and perhaps about 20,000 other species of fish, evolved after this third genome duplication event. The correlation is between genome doublings and morphological diversity.
Minnows belong to a group of fish that has the most diversity of any group of vertebrates.