Vertebra
Irregular bone, part of the core (axial) skeleton
Also known as: Spine bone or backbone
Classification
Irregular bone, part of the core (axial) skeleton
Dimensions
Vary wildly depending on the species and position along the spine, ranging from the tiny, delicate disks of a small rodent to the massive, spool-shaped blocks of a large ungulate or marine mammal.
Key Features
Characterized by a central, spool-shaped main body (centrum) and various projecting bony arms and plates that form a protective tunnel for the spinal cord and provide attachment points for muscles.
Similar Bones
Can sometimes be confused with fragments of skull plates or complex joint ends of long bones, but the presence of the central hollow canal for the spinal cord and the spool-like body make a vertebra easy to distinguish.
Across Species
Vertebrae show incredible diversity across the animal kingdom. In fish, they are simple hourglass shapes that allow for side-to-side tail swishing. In mammals, they develop complex interlocking bumps and ridges that support the body against gravity while allowing for bending, twisting, and shock absorption. Birds have specialized neck vertebrae that allow for extreme head rotation, while whales have flexible vertebrae that assist in vertical propulsion through water.
Evolutionary History
The backbone is one of the defining features of vertebrates, evolving over 500 million years ago from a simple flexible rod called a notochord into a segmented chain of bony blocks designed to protect the central nerve cord and anchor powerful swimming and walking muscles.
Photography Tips
Photograph from the side to show the profile and height of the central body, and from the top or bottom to reveal the inner channel where the spinal cord passes. Include a coin or ruler next to the bone for scale.