The Collaborative International Dictionary of English v.0.48:

kangaroo rat \kangaroo rat\ n. (Zool.)
   A jumping rodent of the genus Dipodomys of the family
   Heteromyidae, which lives in arid regions of Mexico and the
   western U. S.
   [PJC]

   2. (Zool.) An Australian mammal of the genus Notomys.
      [PJC]

   3. (Zool.) a small ratlike Australian kangaroo of the genus
      Potorous, also called the potoroo.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Potoroo \Po`to*roo"\, n. (Zool.)
   Any small kangaroo belonging to Hypsiprymnus, Bettongia,
   and allied genera, native of Australia and Tasmania. Called
   also kangaroo rat.
   [1913 Webster]

WordNet (r) 3.0 (2006):

potoroo
    n 1: Australian rat kangaroos