Animals with weakest bones

 1.  Birds

          Birds those fly, have light weight and hollow bones to reduce body weight and make flight more easier.

2.  Bats

            Like birds, even bats have light weight bones to aid flying. They are the flying mammals.

3.  Amphibians 

               Amphibians like frogs have less denser bones.  This adaptation makes them to stay buoyant in water and move easily on ground.

4.  Reptiles 

               Reptiles such as snakes have less denser bones.  Their skeletal structure is more adapted to movement than strength.

5.  Fish

               Fish found in deep sea have lighter and less denser bones. This adaptation helps them to conserve energy and maintain buoyancy in deep ocean water.