Owl Monkey (genus "aotus") The nocturnal anthropoid

Owl monkeys, also called night monkeys, are the only nocturnal monkey. They are native to Central and South America and they live in family groups with a male, a female, and one or two young. Owl monkeys prefer to eat small ripe fruit, at night they have less competition from other fruit eating animals and predators. They also eat leaves and insects, and at night they can find larger insects than during the day. They spend all of their time living in trees.

The fathers primarily care for the offspring and they are monogamous. The male carries the newborn after the first week, and they only hand the young to the female for suckling. They also have a special dedicated personal grooming toe on each foot, they typically weigh about one kilogram. There are ten known species of owl monkeys, though the only easily distinguished differences are red or grey neck fur.

To read more about owl monkeys, try these references:

Wikipedia - has a great summary now but they call them Night Monkeys.

Wikispecies - has the full classification, as well as the larger familia Aotidae

ARKive - pictures of the colombian owl monkey

Jonathan Greenberg's 1997 paper - a great summary of the species as of that date

Jonathan Greenberg's Other Papers - a researcher's web site dedicated to his owl monkey papers.

Family Cebidae - Sean Flannery's species details for Primate Family Cebidae including owl, spider, howler, tit, and other monkeys.

Aotus: The Owl Monkey - a hard cover collection of recent papers about them. A tad expensive and more than you wanted to know.

Replica Owl Monkey Skull - a haven't seen these in person, but they're impressive with the huge eye sockets.