Example of a vertebra from the caudal section of an Apatosaurus specimen
Vertebra, vertebrae in plural, is a series of complex bones that make up the spine, or backbone. The presence of this bone structure is a key attribute in all members of Vertebrata, known as vertebrates. The vertebrae is segmented and protects the spinal cord, found in all chordates, and acts as the central connection point for most of the rest of the skeletal system. The hagfish are the only known extant vertebrate that still possesses a notocord for support in adulthood, which remains embryonic and ancestral for all other species.
There are 5 sections to the vertebral column for different parts of the body in tetrapods, as fish don't have a need for categorization:
- Cervical: all vertegrae located in the neck, attached to the skull. In reptiles, these may have ribs, of which saurischian dinosaurs and lizards can be quite large for their larger and wider necks. In birds, these ribs are completely fused to the vertebrae. Considered the most flexible of the sections.
- Thoracic: directly below the cervical vertebrae and directly attached to the ribcage. These are generally robust for better support of the body. In a human context they may be labeled "dorsal vertebrae".
- Lumbar: This makes up the rest of the main spine in the torso, directly below the thoracic section and making up the "lower back" below the ribs. Lumbar vertebrae are generally the largest vertebrae in the spine. This term is most often used with mammals.
- Sacral: This vertebra, known as the sacrum, is fused to the hips of the animal, ending the torso. These make up no individual discs unlike other sections.
- Caudal: These are known as the tail vertebrae, and are named the coccygeal vertebrae for humans and tailless primates, as their tailbone is shortened. The number of these vertebrae can range from a few to dozens, of which the most impressive are displayed in the sauropods.
Articulation[]
The vertebral column acts mostly for protection and support of other bones, so despite its size, each individual vertebra cannot move very much. In tandem, the spine can flex and rotate but only to a degree, as any further could damage the spinal cord inside.
Some animals may display extreme length of spine processes to create humps, sails, or finlike structures, most notably from Dimetrodon and its relatives, some spinosaurids, and humped mammals.