They were likely not native to the Time Lord homeworld. The Fifth Doctor once told Tegan that his first incarnation and a Time Lord contemporary known as Ruath "introduced cats into Gallifrey's ecosystem", but he did not indicate where the cats had originated. (PROSE: Goth Opera) At some later date, one of the Presidents of Gallifrey had a pet cat. It was eaten by a mouse that had been enlarged by the Rani in an experiment. (TV: The Mark of the Rani)