Why is mammal coloration so dull?

-an angry Mandrill photographed by David

When was the last time you came across a green monkey? Or a red and blue squirrel? Never. Well, neither have I. But, then we come across colorful insects, birds, and reptiles…so what’s up with the mammals? Why can’t they all be as colorful as the mandrill shown in the picture above!?

Well, it turns out that for much of their evolutionary history, mammals were nocturnal and most modern mammals have inherited the ocular design of their forebears along with red or green color-blindness. Mammals evolved during the Triassic with dinosaurs but during the Mesozoic era(252-65 million years ago) they adopted a nocturnal lifestyle in order to avoid predation from dinosaurs. During that period a trade-off occurred: having less color-sensitive cones in the retina, you can increase the number of light-sensitive rods in the same area, and so improve vision in poor lighting conditions. All of this is supported by research on the ‘nocturnal bottleneck hypothesis’.

On the other hand, it appears that primates and some marsupials are the only mammals to re-develop color vision, possibly due to their frugivorous diet as this is useful in determining whether fruits are ripe or not. And of these mammals, the Mandril among others have developed colorful patterns as mating signals. But, even in the event that all mammals had great color vision I doubt the large carnivorous mammals that inhabit grasslands/forest would develop colorful pigmentation. In fact, it’s in their best interest to remain camouflaged in order to improve their chances of ambushing prey. Applying similar reasoning to these animals’ prey, it’s not surprising that herbivores in grasslands/forests have earthy colors as well.

If you have any thoughts on this subject, feel free to comment. As with everything else on my blog, I’m not an expert on this topic.