Lizard King

The Lizard Kings were the Mondasian equivelant of Earth's Silurians. They lived on Mondas alongside the human-like Mondasians and the Mondasian Sea Devils, although it could be that they too were called Lizard Kings.

History
The Cybermen sent out a cybership to the Dark Continent to search for the lost Lizard Kings, to only end up finding fossilised statues of them. (DWM: The Cybermen)