Sea Devils

Intelligent reptilian life form which ruled the Earth during the Cretaceous (136 to 65 million years BC), and not the Silurian (430 to 395 million years BC).  They and their "cousins", the Silurians, were eventually driven to hibernate in underground shelters by some undetermined cosmic event.  A commando of Sea Devils awoke from suspended animation in 1973 and began sinking ships in the British Channel.   They were contacted by the Master who offered to ally himself with them.  The Third Doctor and the hief Sea Devil talked peace, but they were thwarted by the interference of the Master and Walker, a civil servant who ordered a depth charge attack.   In the end, the Doctor was forced to engineer an explosion which destroyed the Sea Devils' undersea base before any more Sea Devils could be awakened.

The Silurian Icthar reanimated a Sea Devil commando led by Sauvix in 2084, and used them to attack Sea Base Four.  His plan was to launch nuclear missiles to provoke a war between the two blocs, and thus eradicate mankind.  His efforts were defeated by the Fifth Doctor.