No green mammals? Easy, where is green? Usually in the trees and in small plants, mammals usually don't live in trees (sloth excepted, but they are brown and have no predators and blend in with the bark). Now, there are green reptiles that live in jungle bushes, and green birds that live in tree tops where they blend in. Green for a mammal is not a good thing, mammals move, like all animals they need to blend in, praire dogs are brown, like dirt, polar bears are white like the snow, etc etc...
The question is, why aren't there any blue terrestial mammals (dolphins and porposies are blue because it suits them in the ocean.
Next week I will try to explain how Joan Rivers (after numerous face lifts) can open her mouth without her skin splitting down the sides and peeling off.