Terrestrial locomotion

Moving on land is called terrestrial locomotion. Animals use many different ways to get around, and why they move varies. This topic is important for understanding evolution, since it shows how aquatic creatures adapted to life on land. On land, animals face less buoyancy and friction than in water, but more gravity. Evolutionary taxonomy groups land movement into three basic types: legged (using limbs), limbless (using the body itself for propulsion), and rolling (rotating the body across the ground). Certain surfaces allow or require special styles. Slippery surfaces like ice and snow let animals slide, using potential energy to help them move. Loose surfaces like sand or scree have low friction but make traction hard. Humans have adapted to sliding on snow and ice with skates, skis, and toboggans. Polar aquatic animals like ice seals and penguins also use the slipperiness of ice and snow. Beavers make a short mud slide called a "beaver slide" from land into water. Humans use cleats to move better in mud. Some snakes sidewind on sand or loose soil. Animals caught in mudflows move involuntarily, which can help spread species with limited natural range. Passive locomotion is less common on land than in sea or air, but hitchhiking via parasitism occurs, as in other habitats. Many monkeys and apes use brachiation—moving by swinging with their forelimbs. The uneven bars in gymnastics resemble this, but most adult humans lack the upper-body strength for sustained brachiation. Other arboreal animals with tails use them in locomotion, at least for minor suspensory behaviors. Moving on steep, uneven ground requires agility and sure-footedness. Mountain goats are famous for navigating dangerous cliffs where a misstep could be fatal. Many animals must move while carrying their young, usually done by adult females. Some, like marsupials with pouches, are adapted to carry young without using their limbs. In other species, young ride on the mother's back and instinctively cling. Some animals have specialized transport behaviors, like the dung beetle rolling a ball of dung, which combines rolling and limb use. **Legged locomotion**

Moving on appendages is the most common land locomotion, used by two major groups with many terrestrial members: vertebrates and arthropods. Key aspects include posture (how the body is supported by the legs), number of legs, and leg and foot structure. There are also many gaits—ways of moving the legs—such as walking, running, or jumping. **Posture**

Posture is how the body is supported by the legs. Vertebrates have three main postures: sprawling, semi-erect, and fully erect. Some animals switch postures depending on mechanical needs. There is no known difference in energy cost between them. The sprawling posture is the most primitive and the original limb posture from which others evolved. The upper part of the limbs is usually held horizontally, the lower part vertical, though the upper angle may increase in large animals. The body may drag (as in salamanders) or be raised (as in monitor lizards). This posture is linked to trotting gaits, and the body flexes side to side to lengthen steps. All limbed reptiles except birds, salamanders, the platypus, and some walking frogs use it. Unusual examples include amphibious fish like the mudskipper, which drag themselves on sturdy fins. Among invertebrates, most arthropods—including insects—have a sprawling stance. There is anecdotal evidence that some octopus species (like *Pinnoctopus*) drag themselves short distances on land using their tentacles, possibly to pursue prey between rockpools. The semi-erect posture is an extremely elevated version of sprawling, typical of large lizards like monitors and tegus. Mammals and birds typically have a fully erect posture, though each evolved it independently. Their legs are placed under the body. This is often linked to endothermy, as it avoids Carrier's constraint and allows prolonged activity.