Megatherium
From Tardis Wiki, the free Doctor Who reference
The megatherium was a mammal native to Earth. By the 21st century, they were extinct. Martha Jones once spotted one, earning herself 500 points in The I-Spyder Book of Earth Creatures. Little else was known about the species. (PROSE: The Last Dodo)
In reality, the megatherium was a type of giant ground sloth.
