Buffalo

Buffalo were cow-like creatures that lived on Earth. Because Roz Forrester's family name, Inyathi, translated as "buffalo", she wasn't allowed to eat a buffalo. (PROSE: The Also People) They were once the dominant species on Earth, but when their Herd-Leader was trapped in ice they degenerated without his mind. The Bovine Leader revived thousands of years later and was able to travel back in time. He found his species were being wiped out by the native Americans and guided Christopher Columbus to America, hoping the Europeans would wipe out the native Americans and save his herd. However the Europeans wiped out the buffalo themselves. (AUDIO: Trouble in Paradise)

The Seventh Doctor and Ace saw living in the Ngorogoro Crater in 1926. (PROSE: Prelude Birthright)

Cultural references to buffalo
The Ninth Doctor told Mickey Smith to use the password buffalo to access a variety of areas of the UNIT website. (TV: World War Three)

Behind the scenes
The DWU fails to use buffalo as a synonym for bison — which it is, in a limited sense. Certainly, North American buffalo are bison. However, the kind the Seventh Doctor and Ace saw in Africa would have been and not at all bison.