This order comprises the largest number of marsupial mammal species, all of which are native to Australia and New Guinea. Two main characteristics distinguish this group. Firstly, they have a pair of large, almost horizontal incisors on their lower jaw without canines and one or three pairs of incisors on their upper jaw. Secondly, they have syndactyly, i.e. the second and third toes on their hind legs are fused over their entire length, leaving two separate claws at the tip. The fifth toe is usually absent, while the fourth one is often hypertrophied.