Bison

 were Earth ruminants K9 once encountered on an unnamed planet in another dimension, partially inhabited by ex-Tellac miners. They lived alongside other Earth animals from widely varying periods of evolutionary history. (AK9: K9 and the Missing Planet)

According to The I-Spyder Book of Earth Creatures, bison were herbivores, and typical prey of the sabre-toothed tiger. (NSA: The Last Dodo)

Behind the scenes
In the real world, bison and buffalo are often synonyms, especially when talking about the type of buffalo found in North America. But the DWU fails to make this connection. Indeed, the implication in some texts, like DWM: Prelude: Birthright, is that the Doctor and friends are encountering which are not bison.