From an article on "ugly animals we should save anyway" (BBC website), photo by dbimages / Alamy

They write: "No prizes for guessing why proboscis monkeys got their name. It’s not clear why their noses are so big, but males tend to have bigger ones than females, so they might serve as a marker of sexual attractiveness – a bit like the feathers of a bird of paradise, but less obviously pretty. They also have complicated digestive systems to help them digest leaves and fruit, and may be the only primate that chews the cud. They are endangered as a result of their habitat being destroyed."