They ranged primarily through shallow inland seas and the like. Most were fish eating marine dwellers with long necks, small heads full of sharp teeth, short tails, wide bodies, and very well developed paddles instead of hands or feet. But there were also shorter neck versions with large heads and powerful jaws that probably were similar to the killer whales of today. Again, because of the puzzles of the fossil records we do not have definitive answers to all the questions on their origons. The Lizards because of their skull adaptations talked about earlier and perhaps other unknown factors have been very successful from perhaps 200 million years ago up to the present.
Fossils are limited but clear on that.
Snakes are the newest of the reptiles and that they appeared somewhat after the first lizards. Very few fossils have been found and most of these are fragmentary so a lot of guess work is needed here. They were probably around for along time living a fossorial or burrowing existence and then returned to the surface toward the end of the dinosaurs reign. The trouble with most histories stories of life on this planet is that once you come to the extinction of the dinosurs everyone now goes on to the mammals. Let's go back and carry the tread of our story onword.