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