Vertebra
Irregular bone; part of the axial skeleton
Also known as: Backbone, spinal segment, or link in the spine
Classification
Irregular bone; part of the axial skeleton
Dimensions
Since animals vary in size from shrews to whales, these bones range from just a few millimeters to over a foot across; they are generally characterized by a thick central body with several projecting wings and a central opening for the spinal cord.
Key Features
A typical vertebrate bone looks somewhat like a butterfly or a puzzle piece. It usually features a large, solid cylinder at the front, a hollow ring in the middle that looks like a window, and several flat or pointed wings sticking out to the sides and the back. These projections often have smooth, flat faces where they connect to the next bone in the chain.
Similar Bones
This bone can sometimes be confused with fragments of the pelvis or parts of the skull base because they both have irregular shapes and openings. To tell them apart, look for the 'ring' structure; a backbone is designed like a circular tunnel to shield the spinal cord, whereas pelvic bones are usually flatter and lack a central cylindrical 'body' attached to a ring.
Across Species
Nature has modified this basic shape for many uses. In fast-running mammals like deer, these bones have long projections for powerful back muscles to attach to. In birds, many of the backbones are fused together to provide a rigid frame for flight, while in snakes, they are highly mobile with specialized 'ball and socket' joints that allow for extreme slithering movements. Some aquatic mammals have very porous, spongy interiors in these bones to help with buoyancy.
Evolutionary History
The spine is one of the oldest structural features in our lineage, dating back to early fish-like ancestors over 500 million years ago. Originally, the spine was a flexible rod called a notochord. Over deep time, hard bony segments evolved to surround and protect the delicate nerve cord, eventually allowing vertebrates to support their weight on land and grow to massive sizes.
Photography Tips
To get the best identification, place the bone on a plain surface and take one photo looking straight through the central hole. Then, take a side-view photo and one from the top down. Always place a common object like a coin, a key, or a ruler next to it so people can see how big it is.