Many species possess the ability to voluntarily and temporarily change their body shape from a rounded cylinder to a wide, ribbon-like form. This physical transformation is known scientifically as dorsoventral compression, indicating compression from the top (dorsal) to the bottom (ventral) side. This shape change is a dynamic action, employed by the snake for various functional purposes in its environment, such as defense or movement.
The Anatomical Mechanism
The ability to flatten the body is rooted in the snake’s specialized skeletal and muscular structure, specifically involving the ribs. Unlike the rigid rib cages of many vertebrates, a snake’s ribs are highly mobile and connected only to the spine, creating a flexible scaffolding along the body’s length. To flatten, the snake engages a complex network of axial muscles that attach to these ribs.
The key action involves the rotation and outward splaying of the ribs, which significantly increases the animal’s width without changing its height. This movement is powered by specialized musculature, including the costocutaneous muscles, which connect the ribs to the scales on the underside of the snake. By contracting these muscles, the snake pulls the ribs outward, changing its typically rounded cross-section to a flattened oval. This modification is temporary and is reversed once the muscular tension is released.
Behavioral Purposes of Body Flattening
The primary reason many snakes flatten their bodies is to deter potential threats through a defensive display. By rapidly increasing their apparent size, they can make themselves look larger and more intimidating to a predator. This visual bluff is a common tactic, aiming to convince an attacker that the snake is too large or dangerous to pursue.
Flattening also plays a role in thermoregulation, particularly in species that rely on basking to maintain body temperature. When a snake flattens its body, it maximizes the surface area exposed to direct sunlight. This allows the reptile to absorb solar radiation more efficiently, leading to faster warming. Conversely, this mechanism can be used to dissipate heat more quickly in overly warm conditions.
Temporary body compression is also used for specialized forms of locomotion, especially in arboreal species. By transforming their cylindrical body into a flatter, airfoil-like shape, certain snakes can generate aerodynamic lift. This shape is integral to the snake’s ability to control its descent and glide through the air.
Species Known for Extreme Flattening
Several species demonstrate extreme forms of dorsoventral compression, often for specific functions. The most iconic example is the Cobra, which uses its neck ribs to form the characteristic hood. This display is a defensive warning, where the snake expands the skin around its neck to present a large, intimidating visual signal. Non-venomous snakes like the Eastern Hognose snake also employ this technique, flattening their head and neck area to mimic a more dangerous species.
The most specialized use of flattening is seen in the Chrysopelea genus, commonly known as flying snakes. These arboreal species launch themselves from trees and flatten their entire body into a concave, ribbon-like cross-section. This extreme flattening is an aerodynamic adaptation that allows the snake to glide and steer through the air for long distances. By creating this specialized shape and undulating their body in flight, the snake generates lift, enabling controlled movement between tree canopies.