Squirrel

Squirrels were typically small rodents, easily identified by their outsized, bushy tails that were almost as long as their bodies.

Encounters with squirrels
The Doctor, his companions and acquaintances occasionally encountered squirrels. When the Demon Magician threw up a huge wall around the TARDIS, the First Doctor used his "magic box" to super-size a squirrel. The Doctor, John and Gillian were then able to cross the wall on the giant squirrel's back. (TVC: A Christmas Story) Later, the Eighth Doctor had a rather more unpleasant time with squirrels. Slake once made some squirrels vampirc and used them to "guard" the Orpheum Theatre, the lair of Slake's vampire clan. When the Doctor and Sam entered the theatre, they were viciously attacked by the vampire squirrels. (EDA: Vampire Science) In an equally bizarre moment, the Ninth Doctor and his cartoon duplicate saw a cartoon squirrel in a cartoon park, after the Doctor had been briefly transported to a cartoon Earth. (DWM: Art Attack)

Breeds
Amongst the known breeds of squirrel were black squirrels.