Basics of Bone

Monday, October 26, 2020
Emily McDowell, OSARC Lab Supervisor and Bioarchaeologist

Above: The structural unit known as an osteon is the pillar of bone strength, dark cavities called Haversian canals feed blood to bone cells and are surrounded by ringed layers called lamellae.

How is bone formed?

In order to be able to identify bone, you must first understand osteogenesis, or the process by which bone is formed. This process of bone formation starts in the womb and is very complex, but we’ll keep it as simple as possible here.

It is important to remember that bone is living tissue, just like the rest of your body. There are several cells that help keep your bones alive through the formation of new bone (osteoblasts), maintenance of bone tissue (osteocytes), and the destruction of old, damaged bone (osteoclasts). This process happens throughout the lifespan of any animal, with growth occurring more rapidly in juveniles and slowing down in adulthood. In the compact outer layer of bone (cortical bone), formation occurs in concentric or “ring” layers called lamellae. The lamellae surround a cavity containing small blood vessels that feed osteocytes; this blood vessel system is known as the Haversian Canal system (see image at top). The whole structural unit is called an osteon! In addition to cortical bone, your body also makes internal trabecular, or “spongy” bone, that is connected by a complex web of spicules with less of a pattern.

How do you identify bone?

Knowing how bone is formed doesn’t automatically make it easier to differentiate bone from not-bone. Shell, rock, and wood can all be suspicious look-a-likes to the untrained eye. Burned items can cause even more difficulties with identification, as charring can cause a white coloring similar to bone. It’s important to remember that bone is compact, yet porous. It has a hard outer layer of cortical bone, with an internal spongy layer of trabecular or cancellous bone. When in doubt, a piece of compact bone can be held under a microscope to look for concentric osteons with the central Haversian Canal cavity. In instances where identification cannot be determined by general examination, it is best to have a Forensic or Physical Anthropologist examine the specimens.

Does this bone belong to an animal?

So, you’ve established that what you’re looking at is indeed a bone. Now you want to know if the bone came from an animal, and if so, what kind? The main differences between animal species will be architectural - or shape - differences and variation in size. These can be easy to imagine if you think of living animals and how they function!

First, let’s talk about the easiest of these differences: size. Animals range widely in size from something small - like a mouse - to large - like a cow You can eliminate certain categories of animals based purely on the size of the bone you’re looking at.

From there you can look at the architecture of the bone. Does it have a long snout? It may be something like a deer or a dog. Horns? Perhaps a cow. Is the bone small and hollow? You may have a bird. Architectural differences between species are highly variable, and your best resource for identifying what type of animal you have will be a book that focuses on animal bone identification.

In some instances, especially when there is no skull present, the bones are fragmented, or share similar characteristics with human bone, it can be difficult to tell if bone is animal. If you are not certain that you’re looking at an animal, you should leave the specimen where it is. Even if you are remotely suspicious, you should not take any chances. The best way to know the difference between human and non-human bone is to be well versed in what human remains look like to eliminate all other options.

Help, I think these bones belonged to a person! What do I do?

First, and most importantly, DO NOT TOUCH OR REMOVE ANYTHING as you could be disturbing a potential crime scene. According to NC law (NC General Statute 70:-29), you should immediately contact local law enforcement. The law enforcement officers will come to the scene and contact the local medical examiner, who will determine if the remains are medicolegal or archaeological. If they are medicolegal, an investigation will be opened. If they are archaeological, the State Archaeologist will be contacted.


Image credits:
Haversian Canal System, image by Berkshire Community College Bioscience Image Library, Wikimedia Commons
Bone Fragments, image by Thomas Quine, CC BY 2.0
Wood Fragments, image by The Metropolitan Museum of Art, Public Domain
Deer Skull, Public Domain