Koalas are tree-dwelling marsupials native to Australia, known for their teddy bear-like appearance but are not bears. They are herbivores, surviving on a diet of eucalyptus leaves, which are hard to digest and low in energy, leading koalas to sleep up to 20 hours a day. Koalas have special physical adaptations, such as sharp claws, opposable thumbs, and fused toes, which help them grip branches. They reproduce by giving birth to a tiny, undeveloped baby called a joey, which then develops further in the mother's pouch.