Phlegethontia is a snake-like amphibian that lived from the Carboniferous to the Permian period. It lived in swamps and probably, unlike most snakes today, spent most of its time swimming in water, like a frog or a newt. Phlegethontia was about one meter long and it ate small animals and insects.
Phlegethontia was found in the Mazon Creek, in Illinois, among other places. The skull had holes in it, and this made it light. My hypothesis is that Phlegethontia evolved this way because a lighter skull would be easier to lift, and therefore it would be easier for Phlegethontia to snatch a flying insect from the air, much like this adaptation makes it easy for a snake to strike quickly. The skull of Phlegethontia is similar to that of a snake.
Phlegethontia looked very much like a snake, suggesting a similar lifestyle, except more in the water than on land. Amphibians like Phlegethontia cannot permanently live on land without getting wet because they would dry out and die.
At one time there was something called Dolichosoma longissima. But this was an incorrect description and paleontologists realized that it was actually a member of the genus Phlegethontia. Now it is called Phlegethontia longissima.