A lizard does have a backbone, placing it firmly within the category of vertebrate animals. This internal skeletal structure provides the body’s main support and protects the central nervous system.
Lizards Are Vertebrates
The classification of an animal as a vertebrate is based on the presence of a vertebral column, commonly known as a backbone or spine. This structure is composed of numerous interlocking bones called vertebrae, which form a protective tube around the spinal cord. Lizards, along with all other reptiles, birds, mammals, amphibians, and fish, possess this defining feature, distinguishing them from invertebrates like insects and worms. The backbone serves as the central axis of this internal framework, connecting the skull to the tail and providing attachment points for the limbs and muscles. This robust, yet flexible, central support system allows a lizard to achieve its characteristic movements and postures.
Anatomy of the Lizard Skeleton
The lizard’s vertebral column is divided into distinct regions, each specialized for a different function. These regions include the cervical vertebrae in the neck, the dorsal (or trunk) vertebrae, the sacral vertebrae that connect to the pelvic girdle, and the caudal vertebrae extending through the tail. The entire spine can contain a significant number of bony segments, with the presacral count often ranging around 24 to 30 vertebrae, depending on the species. A common feature among many lizard vertebrae is the presence of procoelous centra, meaning the front surface of each vertebral body is concave and the rear is convex. This ball-and-socket arrangement allows for a greater range of motion between successive vertebrae without compromising stability. The sacral region typically consists of two vertebrae that are fused to articulate with the hips. The dorsal vertebrae are connected to ribs, which form the rib cage, protecting the internal organs.
Unique Spinal Adaptations
The structure of the lizard’s backbone is highly adapted to its terrestrial lifestyle, allowing for the undulating, side-to-side movements typical of many species. This lateral flexibility is achieved through the numerous, mobile joints between the vertebrae, enabling rapid changes in direction and efficient locomotion across varied terrain. The overall design prioritizes agility over rigid support. One specialized feature is caudal autotomy, the ability of many lizards to voluntarily shed their tail as a defense mechanism. This process is made possible by intravertebral fracture planes, which are pre-formed zones of weakness that run across the middle of specific caudal vertebrae. When threatened, the lizard contracts muscles around these planes, causing the vertebra to break cleanly. The detached tail often continues to twitch to distract a predator. The regenerated replacement contains only a rod of cartilage.