Fish in shallow waters learned to breath air as a matter of survival. A variety of lobe finned fish took a liking to land (plenty of big bugs to eat and no sharks) and evolved into a "Tetrapod Amphibian", This chart shows its descendents (for simplicity extinct (thus inedible) and minor lines and some intermediate phases have been omitted).

• Synapsids (mammal-like reptiles)
  • Mammals (that's us)
• Amphibians (Salamanders, Frogs)
• Anapsids - Turtles
• Diapsids
  • Lizards and Snakes (Lepidosaurs)
  • Archosaurs
    • Birds (and all other Dinosaurs)
    • Crocodiles & Alligators and Caymans and Gharials

Alligator - [American Alligator Alligator mississippiensis, Chinese Alligator Alligator sinensis]
Alligators are now known not to be reptiles but related to birds through a common dinosaur ancestor. American alligators are found in the southeast of the U.S. from North Carolina down and around Florida to the coastal areas of Texas but most live in Florida and Louisiana. The largest alligator on record was over 19 feet but they are commonly around 8 feet.

While the American Alligator is doing well and is also extensively farmed, the Chinese alligator lives only along the Yangtze River and is endangered. In the U.S. alligator has been harvested primarily for hides but the meat is becoming increasingly popular. Prep & Cooking Details

Frog - [family Ranidae (true frogs) mostly genus Rana (over 230 species)]
While one species of frog (Conraua goliath) can grow to 7 pounds, the edible frogs of commerce are generally less than 1 pound. While frog eating is commonly associated with France, they are much more commonly eaten in the U.S. South and Midwest, the Caribbean, China and Southeast Asia. In most cases only the hind legs are eaten though in some areas for some species the back is also used.

Frozen frog legs from China and Vietnam are now common in U.S. markets serving local Asian communities. In Europe the most eaten frog is the Edible Frog (Rana kl. esculenta). In the U.S. the most eaten frog is the American Bull Frog (Rana catesbeiana), a very large frog that can grow to 1.5 pounds and is farmed in some areas. Prep & Cooking Details

Iguana - [Green Iguana Iguana iguana]
The Green Iguana is native to Central and South America and the Caribbean Islands and grows to 6 feet long and over 10 pounds. Iguanas hatched in captivity make good pets if given proper care and feeding which may not be easy in non-tropical locations. Wild iguanas seldom survive in captivity.

While green iguanas are eaten in Central and South America they are CITES (Convention on International Trade in Endangered Species) listed as Appendix II "threatened" so I don't recommend eating them. They should also not be purchased as pets unless their fairly demanding care and feeding needs can be met - for a period of 20 years or more. Prep & Cooking Details

Rattlesnake - [genus Crotalus, (27 species), also genus Sistrurus (3 species)]
Rattlesnakes are native to North and South America and are among the most venomous snakes in the world. Some species can grow to more than 8 feet long but the famous Western Diamondback rarely exceeds 6 feet. Rattlesnakes figure in the cuisines of the U.S. Southwest and Mexico and are available from specialty meat stores. The flavor is similar to a free range chicken thigh but chewier. Prep & Cooking Details

Turtles - [order Testudines, family Geoemydidae (Asian river turtles, Asian box turtles), family Trionychidae (softshell turtles), family Emydidae (American box and pond turtles), family Chelydridae (snapping turtles)]
The first known turtle is from the early Triassic, more than 240 million years ago and long before modern lizards and snakes appeared, but it was so well developed there were probably turtles long before that. Originally land animals, a fair number of species took up life in the water and some even became sea creatures, but they still need to come onto land to lay their eggs.

Turtles are traditionally grouped with the Anapsid reptiles but some paleontologists now believe their anapsid style skull was a reversion from a Diapsid form which would make Anapsids totally extinct.