Crocodiles, sea turtles and sea snakes are marine reptiles instantly recognisable to everyone. These animals all have relatives living in fresh water or even on land, and all must surface regularly to breath. The only lizard in this group is the Galapagos marine iguana, and it only enters the sea to feed on seaweed (marine algae). Most of its life is spent sunbaking on rocks along the shore.

• Lungs, as all reptiles must regularly breath air.
• Scaly skin, at least on the legs as in sea turtles.
• To be cold blooded with no internal mechanism to increase the body temperature above the water temperature.
• To live mainly in warm tropical and sub-tropical seas.
• To have hatchlings that are miniature replicas of the adults (direct development).
• Salt glands to concentrate and excrete excess salt from the body.