Post #3789649

"Until the 1960s, popular belief held that most mammals outside of primates were monochromats. In the last half-century, however, a focus on behavioral and genetic testing of mammals has accumulated extensive evidence of dichromatic color vision in a number of mammalian orders. Mammals are now usually assumed to be dichromats (possessing S- and L-cones), with monochromats viewed as the exceptions. The common vertebrate ancestor, extant during the Cambrian, was tetrachromatic, possessing 4 distinct opsins classes. Early mammalian evolution would see the loss of two of these four opsins, due to the nocturnal bottleneck, as dichromacy may improve an animal's ability to distinguish colors in dim light. Placental mammals are therefore – as a rule – dichromatic. (...) Old world monkeys and apes re-evolved trichromacy." https://en.wikipedia.org/wiki/Dichromacy#Mammals