Quadrupedalism

Quadrupedalism is a mode of locomotion in which an animal moves on all four limbs. It is the dominant form of terrestrial locomotion among mammals and is present in many reptiles and amphibians. Quadrupedal gait provides stability, supports body weight, and allows rapid acceleration and maneuverability on varied terrain.

Anatomy and mechanics: In quadrupeds, limbs are positioned beneath the body or directed outward, depending on lineage, with digits or hooves for weight transfer and traction. The forelimbs often contribute to steering and braking, while the hindlimbs primarily drive propulsion. Limb length, joint range, and spinal flexibility shape balance, speed, and endurance.

Gaits: Many quadrupeds use a progression of gaits. A walking gait keeps all limbs in contact with the ground, a trot uses diagonal limb pairs, a canter is a three-beat gait with a moment of suspension, and a gallop is a fast, usually four-beat gait with longer suspension. Some species also employ pacing, a two-beat lateral gait, or bounding.

Evolution and variation: Quadrupedalism has evolved multiple times across vertebrates. In mammals, many lineages are primarily quadrupedal, with specialized adaptations for speed (cursorial forms), climbing, or digging. Among primates, quadrupedal travel is common on the ground or in trees, while some lineages are predominantly suspensory or brachiating. Humans are bipeds but share a common quadrupedal ancestry.

Ecological and behavioral implications: Quadrupedal locomotion shapes habitat use, foraging, predator avoidance, and social dynamics. It interacts with body size, limb morphology, and environmental structure to determine efficiency at different speeds and terrains.