Lizards possess bones, classifying them as vertebrates. They are reptiles belonging to the order Squamata (shared with snakes) and the suborder Lacertilia (Sauria). The complete internal skeleton provides structure and support for their varied lifestyles, from burrowing to climbing.
Lizards as Vertebrates
A lizard’s bony framework is an endoskeleton, meaning the skeleton is housed entirely inside the body. This internal structure is composed of a well-developed skull, a long vertebral column, and a rib cage protecting internal organs. The axial skeleton, including the skull and spine, forms the central axis of the body.
The vertebral column, or backbone, is a chain of individual bones running from the skull base to the tail tip, providing flexibility and anchoring muscles. The rib cage is composed of numerous ribs that articulate with the vertebrae, forming a protective enclosure for the heart and lungs. This arrangement allows the lizard to maintain its body shape and move effectively across various terrains.
Unique Skeletal Adaptations
Lizard skeletons feature specialized adaptations beyond the basic vertebrate blueprint, particularly in the tail structure. Many species exhibit caudal autotomy, or voluntary tail shedding, a defensive mechanism made possible by specialized bony anatomy. This ability relies on intra-vertebral fracture planes, which are pre-formed lines of weakness running across certain caudal vertebrae.
When grabbed, muscle contraction around these planes creates a forceful snap, cleanly breaking the bone at this predetermined point. The shed portion of the tail continues to twitch, distracting the predator while the lizard escapes. The tail that regrows after autotomy is supported not by new bone, but by a rod of cartilage.
The appendicular skeleton, consisting of the limbs and supporting girdles, allows for the characteristic sprawling gait. Furthermore, many lizards possess a kinetic skull, where the bones of the upper jaw and cranium can move relative to one another. This flexibility allows for complex jaw mechanics and a wider gape, which is advantageous for capturing and manipulating prey.
Skeletons of Legless Lizards
Legless lizards, such as the glass lizard or slow worm, possess a full bony skeleton. The loss of external limbs is an evolutionary adaptation that occurred independently in several lizard lineages, often associated with a burrowing lifestyle. Despite their snake-like appearance, these lizards retain distinct skeletal features that separate them from true snakes.
Legless lizards typically have an elongated vertebral column but still possess vestigial pelvic or pectoral girdles—remnants of the shoulder or hip bones—internally. This skeletal trait is one that most true snakes lack entirely.