Waaay back in my 2E gaming days, I had all the lizard folk descended from a single pre-human lizardish race. This race, called the Samat, were incredibly powerful mages, way beyond anything humans and their kin are capable of. I brought up the whole concept for an adventure where the PCs came upon the buried tomb of a Samat and accidently resurrected it... most of them lived to regret it.
Through a roundabout process, the samats ended up in the Nyambe: African Adventures book from Atlas, where they got altered into a snakish creature and (in that world at least) were the ancestors of the yuan ti....