Laluni

The Lalunis were a species of metamorphic beings that were after the secret of time travel for years.

Trahlen and "Kyle" were two Lalunis, trapped on an alien zoo to try and get time energy that was leaking out around the planet. Trahlen turned into a crocodile, and became nicknamed "Time Crocodile" for his ability to temporarily travel through time, and Kyle was a tortoise.

Later, they became both humanoids, but with a crocodile and tortoise head. They were defeated by the Doctor, and a mysterious alien Time Agent took them away. (DYD: The Time Crocodile)