Newts are a type of salamander belonging to the class Amphibia. They are classified as vertebrates, meaning they possess an internal skeleton constructed of bone and cartilage. This bony endoskeleton provides the necessary framework for their body shape and supports their movements across both aquatic and terrestrial environments.
Classification and the Basic Answer
Newts belong to the phylum Chordata and the subphylum Vertebrata, which includes fish, reptiles, birds, and mammals. As vertebrates, newts possess a vertebral column, or backbone. This classification distinguishes them from invertebrates, such as insects or worms, which lack this internal, segmented bony structure. Their placement in the order Urodela, alongside other salamanders, confirms that the newt’s body plan is built around this support structure.
Structure of the Newt Skeleton
The newt’s skeleton is divided into two main parts, following the standard vertebrate plan: the axial and the appendicular skeletons. The axial skeleton forms the central axis, consisting of a lightweight skull and a long, flexible vertebral column that extends into the tail. The appendicular skeleton includes the bones of the four limbs and the pectoral and pelvic girdles that attach them to the body.
The skeleton is relatively unossified compared to that of other terrestrial vertebrates, retaining a higher proportion of cartilage even in the adult form. Cartilage is prominent in the joints and younger life stages, providing flexibility for aquatic movement. This combination of bone and cartilage creates a lightweight yet resilient structure, allowing the newt to manage both water buoyancy and gravity on land.
How Bones Support Locomotion and Life Stages
The newt’s skeletal structure is adapted to accommodate its semi-aquatic life cycle, supporting two different modes of locomotion. In the water, the highly flexible spine is the primary engine for movement, facilitating the lateral undulation that propels the animal forward while swimming. This serpentine movement is efficient in the dense aquatic environment and is common across many aquatic vertebrates.
When moving onto land during the terrestrial eft stage, the bony limbs and girdles support the body against gravity. Newts walk with a sprawling posture, where the humerus and femur are held horizontally, representing a primitive form of tetrapod walking. The vertebral column still plays a role by bending laterally to lengthen the stride and shift the body weight. The calcified bones provide the leverage for muscles to lift the body and overcome the inertia of movement on solid ground.
The Unique Ability to Regrow Bone
The newt’s skeletal system has an unparalleled capacity to regenerate completely after injury. Newts can regrow entire limbs, including all internal bone structures, as well as parts of the jaw and spinal column. This regenerative feat begins with dedifferentiation, where mature cells near the site of amputation revert to a primitive, stem cell-like state.
These specialized cells accumulate to form a mass known as the blastema, which is capable of redifferentiating into all the missing tissues. Within the blastema, cells rebuild the lost skeletal elements, forming new cartilage that is subsequently replaced by bone tissue. This allows for flawless repair without the formation of scar tissue, demonstrating a mechanism for complete skeletal restoration that is virtually unique among four-limbed animals.