The Colobus Monkey is unique in that it has a digestive system similar to ruminants (cattle, goats). It has a pouched stomach which allows it to digest plant-based diets more easily.
Colobus monkeys live in small groups with a single male and many females and offspring. The offspring are born completely white and then turn black as they grow older
They also lack thumbs, probably as an adaptation to move through the trees more quickly.