In Doctor Who Series 5 Episode 8, "The Hungry Earth", the Doctor says that the Silurians are ancient inhabitants of Earth, not aliens:
DOCTOR: They're not aliens. They're Earth-liens. Once known as the Silurian race, or, some would argue, Eocenes, or Homo Reptilia. Not monsters, not evil. Well, only as evil as you are. The previous owners of the planet, that's all. Look, from their point of view, you're the invaders.
But in Series 7 Episode 2, "Dinosaurs on a Spaceship", he sends Amy and Rory a postcard from 'Siluria':
But if the Silurians are from Earth, then what and where is Siluria?
Are they really originally from Earth, or did they come from this Siluria and just colonise Earth before humans came along?