When a bone is discovered, it can be difficult to determine if it's from a human or an animal. If the bone is from a non-mammalian skeleton, it's easy to tell if the bone is human or not human, e.g., bird bones are significantly tinier and more fragile than human bones. However, non-human mammalian bones can be more difficult to differentiate from human bones, though not impossible.
Carefully place the bones being identified on the flat surface.
Collect the disarticulated and articulated skeletons to assist with bone comparison, placing the articulated skeleton on the flat surface.
Retrieve the preferred reference books. Tim D. White's "Human Osteology" is a good, detailed text that can be ordered through any bookstore or online. William M. Bass's "Human Osteology: A Laboratory and Field Manual" is another fine choice that can be purchased used online.
Determine if the bone is human or nonhuman by comparing the skeletal anatomies of the bone being identified with the reference skeletons.
If the bone is a skull, a human skull will have a flat face, a large brain cavity, an inferior placed foramen magnum (the large hole in the skull where the spinal cord inserts), a chin, frontally placed eye sockets and a U-shaped mandible. An animal will have a projected face, where the muzzle extends from the jaw; obvious raised markings where muscles attach; no chin; eye sockets located on the side of the face; and a V-shaped mandible.
If the bone is from the body, the upper bones (such as the arm bones) will be thin and fairly straight if from a human--animal bones are more robust. The radius and ulna will be separate. The vertebrae (or spine bones) will be flat and broad, with convex and concave surfaces. Human pelvises and sacrums are flat and broad, and include five fused vertebrae, while an animal's pelvis and sacrum are long and narrow, with three or four fused vertebrae. A human's tibia and fibula will be separated. A human's foot is long and narrow, while an animal's foot is broad.
Analyse the bone's macrostructure. A human bone will have porous cortical bone; an animal's won't. (Cortical bone is the dense solid bone on the walls of bone shafts and external bone surfaces.) For a human, the cortical bone thickness on the humerus and femur (the large arm and large leg bones) is about one-fourth the thickness of the diameter of the bone, while an animal's cortical thickness is one-half the thickness. Humans have spongy textured interior bones; animals don't.
The bone can be sent to a lab to analyse how the bone tissue is organised to determine if the bone is human--the layout of human tissue is different from animal tissue; however, because of individual and species variation, this method isn't perfectly precise.
DNA analysis can also be performed on the bone; however, this will cost thousands of dollars.
Many major medical schools or forensic labs can perform these services.
Be patient. It takes time to learn to differentiate human bones from animal bones. "The Human Bone Manual" by Tim D. White is an excellent resource for beginners, and can be ordered through any major bookstore or online. Tim D. White's "Human Osteology" is a good choice for those who would like a more detailed approach to bone identification, and can also be found online or though a bookstore.