> The earliest true mammals evolved from therapsid ancestors during the Early Jurassic, somewhere around 200 Ma.
Um, what? I would have put the date either earlier or later than that, depending on whether we talk of last common ancestor of all existing mammals or the divergence date of mammals from sauropsida. But all that begs the question: how do you define a “true mammal” when mammary glands do not show up in fossil records? Pick an arbitrary date?
> All four of the cone opsin gene families emerged at a point early in vertebrate evolution, perhaps as long as 540 Ma
That is very long ago, we’re talking what, ah, Cambrian explosion. “All four”, where we have … only two with a non-functional third in monotones.
> monotremes diverging from other mammals approximately 166 Ma, while marsupial and eutherians subsequently diverged approximately 148 Ma.
That’s shockingly early, comparable with early dinosaurs.
> Rh2 in marsupials … conflicting results from studies.
> the majority of contemporary mammals in containing two types of cone pigment.
> The relative spectral positioning of the cone pigments varies widely among mammals.
Three colour vision is present in several monkeys, by duplication of the LWS pigment group. Not in all monkeys, and not all at the same frequencies. Ditto lemurs.
> Although three (or more) types of cone pigments are common among vertebrates, in eutherian mammals only primates have three cone pigments, and even among them that arrangement is far from universal.
> All contemporary catarrhine primates (Old World monkeys, apes, humans) have two LWS genes that are positioned in a head-to-tail tandem array.
> There is no evidence for evolution of a third cone pigment in any non-primate eutherian mammal.