Animals of different classes have extremely different bones, varying in size, structure and even material
Mammal bones are made from calcium and phosphorus and contain spongy marrow. Bird bones are hollow with criss-crossing struts to maintain their structure. Some fish bones, like those of rays and skates, are made from cartilage rather than calcium.
The mammal skeleton supports the body’s form and attaches to muscles to help the body move. The general skeletal plan is the same for all mammals with the head at one end, two forelimbs, a spinal column and two hind limbs (with the exception of marine mammals). When comparing almost any two mammal species the bones are in roughly the same place, but may be differently shaped.
Birds have evolved to be as light as possible to aid their flight, with the mute swan being one of the heaviest birds that can fly. Bird bones are filled with spongy marrow, and a cross section is similar in appearance to a slice of ciabatta bread.
Sharks and rays have skeletons made from lightweight cartilage. This is highly flexible and allows them to launch themselves out of the water.