Proboscis monkeys

Excerpts from a longread at the always-interesting Hakai Magazine:

Composure aside, the proboscis monkey is most famous for its looks. The female has a sweet face with an upturned nose; bright, wide-open eyes; a pudgy belly. The male is more … striking. A pronounced brow cloaks his eyes and his nose can reach an impressive 17.5 centimeters long—a smidge longer than an iPhone X—a protuberance straight out of a Roald Dahl book. Bulbous. Fleshy. Floppy. His stomach is so Dahlishly pronounced, it’s perhaps the best example ever of the word potbelly. The paunch, the hooded eyes, and the fur piled on his shoulders like loose skin add to the furry–old man look... 

Confirmation bias has undermined our understanding of the monkey: researchers assumed the proboscises prefer water because boats were the main method of human travel for most of Borneo’s history. Conveniently, they saw the monkeys in trees on ocean and river shorelines at dawn and dusk, and pushing further into the forest seemed unnecessary... 

The Kinabatangan proboscis monkeys are also, so far, the only primate known to chew their cud—they regurgitate a meal to chew it again, like cows.. They found that seeds traveling through a proboscis’s gut were much more likely to germinate than the other seeds. Also, seeds from unripe fruit were more likely to germinate than seeds from ripe fruit. So, given their use of habitat, proboscis monkeys were providing a service: they were dispersing intact seeds far from the parent plant to suitable riverine habitats...

In a group of studies that took over 15 years, Matsuda and others on Team Proboscis found the best evidence yet to explain the big nose: the ladies like it. The bigger the male, the bigger the nose and the bigger the testes. 

More photos and a couple gifs at the link.  And I recommend exploring the rest of the magazine.