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. (PROSE: K9 and the Missing Planet)

According to both The I-Spyder Book of Earth Creatures and the Tenth Doctor, bison were herbivores, and typical prey of the sabre-toothed tiger. (PROSE: 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. However, the DWU fails to make this connection.  Indeed, the implication in some texts, like PROSE: Prelude Birthright, is that the Doctor and friends are encountering  which are not bison.