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 cretacean period.
Their extinction occurred 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 fertilisation as gametes cannot survive on
land.
(iii) Shell around the egg to check desiccation.
(iv) Fluid-filled amnion around the embryo to provide
aquatic environment for development on land.