Flying squirrel

Flying squirrels are a tribe of 44 species in the squirrel family Sciuridae. Despite the name, none use powered flight: all are gliders.
They are sociable, noisy rodents that glide from tree to tree, using a flap of loose skin that connects their front and hind legs. They can glide up to 150 feet (46 m), steering with their tail, and landing on tree trunks, gripping it with all four feet.
These squirrels are nocturnal (most active at night). They have a life span of about five years in the wild, and about 13 years in captivity. Flying squirrels live in forests in North America, Europe and Asia. 
Flying squirrels eat mostly plants, like seeds, nuts, leaves, maple sap, bulbs, bark, flowers, and roots. Less often, they eat insects, eggs, worms, small birds, and other small animals.
Flying squirrels are hunted by weasels, foxes, hawks, and coyotes.
Evolution.
Before the 21st century, the evolutionary history of the flying squirrel was often debated. This debate was clarified by two recent molecular studies. These studies found that the living flying squirrels originated 18–20 million years ago, are monophyletic, and have a sister relationship with tree squirrels. 
There are reasons which may explain why gliding has evolved in mammals: