Largest burrowing mammal

The largest burrowing mammal is the wombat (Vombatus ursinus) of Australia and Tasmania. These squat, bear-like creatures can measure up to 1.2 m (4 ft) and weigh up to 35 kg (77 lb). Their backwards-opening pouch, large paws and strong claws assist them in digging burrows, which can be up to 20 m (65 ft) long and 2 m (6 ft) below ground, with inter-connecting tunnels.

http://www.pbs.org/edens/tasmania/featured.html
http://www.parks.tas.gov.au/wildlife/mammals/wombat.html
http://www.enchantedlearning.com/subjects/mammals/marsupial/Wombatcoloring.shtml