Lethiscus is the earliest known representative of the Aïstopoda, a group of very specialised snake-like amphibians known from the Carboniferous and Permian. Lethiscus is known from only a single specimen from the Holkerian Stage (Middle Viséan) of the Early Carboniferous (Middle Mississippian) of Scotland, and is one of the oldest known post Devonian tetrapods. Despite its very early date, it was already a highly advanced animal.