A discussion on a forum called QI also has information about this word's origin. Judy Bennett says:
Lieutenant James Cook beached his 'HM Bark Endeavour' in what is now Cooktown, in 1770 having damaged his ship on the Great Barrier Reef. He remained in the area for nearly seven weeks. The word 'kangaroo' was first recorded in the ships' journals during this time, and the animal was also drawn by Sidney Parkinson. The journals are held at the James Cook Museum in Cooktown. The first sighting of the animal was on June 24th 1770. They tried to shoot one for quite some time, finally Lieut. John Gore succeeding on July 14th. It was eaten at supper the following day.I've posted about this word previously.