Sierra Leone - Gibbon Monkey - $1 - 2011 - Brilliant Uncirculated Crown - Gibbons are apes in the family Hylobatidae. Gibbons occur in tropical and subtropical rainforests from northeast India to Indonesia and north to southern China, including the islands of Sumatra, Borneo and Java. Also called the lesser apes, gibbons differ from great apes (chimpanzees, bonobos, gorillas, orangutans and humans) in being smaller, exhibiting low sexual dimorphism, in not making nests, and in certain anatomical details in which they superficially more closely resemble monkeys than great apes do. Gibbons also display pair-bonding, unlike most of the great apes. Gibbons are masters of their primary mode of locomotion, brachiation, swinging from branch to branch for distances of up to 50 feet, at speeds as high as 35 miles per hour. They can also make leaps of up to 26 feet and walk on two legs with their arms raised for balance. They are the fastest and most agile of all tree-dwelling, non-flying mammals. Depending on species and gender, gibbons' fur coloration varies from dark to light brown shades, and anywhere in between black and white. It is rare to see a completely white gibbon.