any of several South American marsupial mammals of the family Caenolestidae. The seven species, together with opossums (Didelphidae), form the New World section of the superorder Marsupialia. Rat opossums, named for their general appearance and size, have 46 to 48 teeth and long epipubic bones associated with the pelvis. The marsupial pouch is lacking in adults. The thick, soft fur is gray-brown. Rat opossums live in cloud forests and high valleys of Ecuador and Bolivia (the five species of the genus Caenolestes) and of Peru (Lestoros, or Orolestes, inca) and in coastal forests of Chile (Rhyncholestes raphanurus). Their habits are little known.