Alligator
From Tardis Wiki, the free Doctor Who reference
Alligators were a type of crocodilian that could be found in the United States and in China.
During the 22nd century Dalek invasion of the solar system, including Earth, many animals escaped from zoos during the plague. Most of them died but reptiles such as the alligators thrived in the sewers. An alligator almost ate Susan but was killed by David Campbell. (DW: The Dalek Invasion of Earth)
