Squirrel

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

Encounters with 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 crossed the wall on the giant squirrel's back. (COMIC: A Christmas Story)

Slake once made some squirrels vampiric and used them to "guard" the Orpheum Theatre, the lair of Slake's vampire clan. When the Eighth Doctor and Sam entered the theatre, they were viciously attacked by the vampire squirrels. (PROSE: Vampire Science)

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. (COMIC: Art Attack)

Squirrels lived in the forests of the Catskill Mountains. They were mostly gone when the Butler Institute got rid of the trees to build a project site, although Brodie saw one after a failed attempt to smash a security camera. They seemed to be returning after the site's destruction. (PROSE: Cat's Cradle: Warhead)

Breeds
Amongst the known breeds of squirrel were black squirrels. (AUDIO: Mother Russia)