Skeletal materials are organics primarily composed of varying percentages of hydroxyapatite and collagen, and can take the form of bone, antler, ivory, teeth, or horn. To first identify whether a material is skeletal, one must look for a porous surface, or unique shape.
Chitin is a skeletal material found in insects and anthropods. ... This skeletal material (chitin) is usually present outside the organism and this makes it an exoskeleton.
Cartilage
Bone

Bone is the substance that forms the skeleton of the body. It is composed chiefly of calcium phosphate and calcium carbonate. Chitin is a major constituent of the exoskeleton, or external skeleton, of many arthropods such as insects, spiders, and crustaceans. The main structural components of our bodies are bone, muscle, and cartilage. Bones are rigid, while muscles bend, stretch, and are flexible. Cartilage connective tissue is the perfect halfway point between these other tissues. It is not as rigid or as hard as bone, and it is also less flexible than muscle. Therefore, we find cartilage in places where we need some support and structure, but a bit of flexibility as well. This includes places such as our joints, our ears, and our nose, as well as in between the vertebrae in our spinal column.