Kangaroos were mammals common to Australia. On at least one adventure with the Eleventh Doctor, Abigail Pettigrew went to Uluru and was photographed in front of a kangaroo crossing sign. (TV: A Christmas Carol)
Immediately after regeneration, the Seventh Doctor's brain was addled, and he unwittingly altered several common metaphors. He claimed that Melanie Bush had the "mind of a kangaroo", before she reminded him that the people with great memories were said to have the "mind of an elephant". (TV: Time and the Rani)
Kangaroos were among the animals on board the Ark circa 10,000,000. (PROSE: The Ark)
The Second Doctor and the Brigadier once fought against aliens that "hopped like kangaroos". (TV: The Five Doctors)
