Lizards evolved from the stem reptiles. This evolution began in the Permian period that is between 299 and 251 million years ago. The stem reptiles or cotylosaurs had solid box like skulls with openings only for the eyes and nostrils. Iepidosaurs evolved from cotylosaurs. They had a lighter skull with an additional opening. Eosuchians were the first of the Lepidosaurs. Lizards evolved from the Eosuchians 250 to 200 million years ago in the Triassic Age.
Some early lizards had ribs rather like the ribs of an umbrella. They supported a folding membrane which, when expanded allowed the animal to glide through the air. Kuehneosaurus from Southern England and icarosaurus which lived in what is now the United Sates had these special ribs? Mossasaurs were giant sea lizards. They ate fish. They reached a length of twelve metres, and swam with the help of paddle shaped limbs. These early lizards died out. Draco, the flying lizards of South East Asia has ribs like the icarosaurus.