The family Phascolarctidae is a small family of marsupial mammals that includes only one extant genus, Phascolarctos, with the well-known koala (Phascolarctos cinereus) as its sole living species. Members of this family are arboreal, folivorous marsupials native to Australia, primarily feeding on eucalyptus leaves, which are low in nutrients and toxic compounds that the animals have specially adapted to digest. Phascolarctids have a specialized cecum and gut microbiota that allow them to extract nutrients from their fibrous diet. They are characterized by a stout, tailless body, strong limbs, and sharp claws for climbing. Fossil records indicate that Phascolarctidae was more diverse in the past, but habitat loss and dietary specialization have restricted them to a single surviving species today.