Overall, the advantage gained from increased sensitivity with wavelength opponency would open up opportunities for future exploitation by mutations and even further improvement.
[3] This indicates that the common ancestor of amphibians and amniotes (≈350 million years ago) had tetrachromatic vision — the ability to see four dimensions of color.
It is postulated that some early monotremes, marsupials, and placentals were semiaquatic or burrowing, as there are multiple mammalian lineages with such habits today.
Since the beginning of the Paleogene Period, surviving mammals enlarged, moving away by adaptive radiation from a burrowing existence and into the open, although most species kept their relatively poor color vision.
[10] A new study published in Biological Reviews proposes that animal color vision emerged approximately 500 million years ago.
[11] This discovery has generated interest and discussion among scientists because it raises important questions about the evolutionary pressures that led to the development of color vision.