During the Jurassic period of Mesozoic era, certain gigantic reptiles roamed on land, swarm in water and flew in the air. These reptiles were called dinosaurs. These animals disappeared during a short time at the end of the cretacecous period.
Their extinction occured due to competition with early mammals or from climatic changes due to the collision of a large meteorite with the earth. The collision must have produced huge dust clouds into the air, screening sunlight from the earth. The lack of sunlight would have destroyed vegetation and cooled the atmosphere. These may be the reason for extinction of dinosaurs.
Reasons for Successful adaptation on land by reptiles are
(i) Horny scales which reduce loss of water.
(ii) Internal fertilization as gametes cannot survive on land.
(iii) Shell around the egg to check dessication.
(iv) Fluid filled amnion around the embryo to provide aquatic environment for development on land.