LOCOMOTION OF VERTEBRATES
In this article, we shall learn how different members of vertebrates undergo locomotion?
There are five categories s of vertebrates, (1) fishes, (2) amphibians, (3) reptiles, (4) birds (5) mammals.
According to the theory of evolution, fishes are considered the ancestors of amphibians. Similarly, amphibians are the ancestors of reptiles, and reptiles are the ancestors of both birds of mammals. Here we relate the locomotion and movement of vertebrates. Skeletal muscles as well as skeleton both responsible for the locomotion in vertebrates.
Locomotion in fishes
The main types in fishes are anguilliform in which a wave passes evenly along a long slender body; sub-carangiform in which the wave increases quickly in amplitude towards the tail, carangiform in which the wave is more concentrated near the tail, which vibrates rapidly; thunniform, rapid swimming with a large powerful or stronger crescent-shaped tail; and ostraciiform with almost no vibration except the tail fin. More specialized fish include movement by pectoral fins with mainly a stiff body, like the sunfish, and movement by propagating a wave along with long fins with a motionless body in fish with electric organs such as the knifefish. In addition, some fishes have the ability to ‘walk’ i.e. move over land, burrow on mud, and glide through the air.
The body of most fishes is streamlined, being tapered at both ends. It means that water flows readily over the body surface and drag is reduced to a minimum. Apart from the fins no other structure Project from the body of fish and it seems that the faster the fish, the more perfect is streamlined. The dermal denticles of cartilaginous fishes and the scales of bony fishes are kept moist by slimy exudation from mucus or oil glands and this also considerably reduces friction between fish and water.
Locomotion in Amphibians
As they evolved from the lungfishes, amphibians had to make some adaptations to live on lands, including the need to develop new modes of locomotion. In the water, the sideways thrusts of their tails had propelled them forward, but on land, quite different mechanisms were required. Their vertebral columns, limbs girdles, and musculature needed to strong enough to raise them off the ground for locomotion and feeding.
In the anurans the complete skeleton and muscular system have become specialized for the specific swimming and jumping methods of locomotion; by means of extensor thrusts of both kinds of limbs, acting together. Frogs and toads, also walk and hop on land due to strong hind limbs. In the water, the webbed hind feet provide a greater surface area for pushing backward on the water. The smaller-force limbs help to steer when the frog is swimming and absorb the shock of landing after a jump on land. On moving from water to land or over rough ground the frog will crawl rather than leap.
Locomotion in Reptiles
Reptiles use different forms of locomotion from place to place. However some lizards walk on all fours, some use only their hind limbs when running. Some snakes and legless lizards move by attaching their belly scales to rough surfaces and pulling themselves forwards.
The lifestyle of reptiles reveals striking adaptations for locomotion. They move better than amphibians due to the evolution of their skeleton. The reptiles use modes of walking and running. The general form of the reptilian skeleton is based on one inherited from ancient amphibians. The skeleton is highly ossified to provide greater support. They contain cervical vertebrae. The first two cervical vertebrae (atlas & axis) provide greater freedom of movement for the head. The axis is modified for rotational movement. The ribs of reptiles may be highly modified. The ribs of snakes have muscular connections to large belly scales to aid locomotion. Many prehistoric reptiles were bipedal meaning that they walked only on hind limbs. They had a narrow pelvis and heavy outstretched tail for balance. Bipedal locomotion freed the front appendages, which became adapted for prey capture or flight in some animals.
Locomotion in birds
The flight is the primary mode of locomotion in birds. Actually, locomotion used most bird species in which birds take off and fly. Bird flight is one of the most complex forms of locomotion in the animal kingdom. Each fact of this type of motion, involving hovering, taking off and landing includes many complex movements.
The skeleton of a bird is modified for flight. The most obvious adaptations are the bones with large air spaces which make them lighter. In birds, the forelimbs evolved into wings with very strong pectoral muscles which pull the wings up and down. The sternum is modified to form a keel. Generally, the keel is required for the attachment of muscles. The body is covered with feathers which gives the wing a large surface area to keep the birds in the air. They also keep their bodies warm, so that they can produce enough energy to fly.
There are two distinct types of flight in birds, (1) passive flight (2) active flight.
Passive flight: When birds glide, the wings act as aerofoils. An aerofoil is any smooth surface that through the air at an angle to the airstream. The air flows over the wings in such a way that the bird is given lift, the amount of lift depends on the angle at which the wing is held relative to the air-stream.
Active flight: When little or no support can be gained from upward air currents, the same effect can be achieved by flapping the wings. As the birds move through the air, the air flows more quickly over the curved upper surface than over the lower surface. This reduces the air pressure on the top of the wings as compared with air pressure below the wing.
Locomotion in mammals
Mammals contain limbs that are specialized for a particular way of moving. They may be specialized in walking, running, jumping, climbing, flying, and swimming. Mammals may have different modes for locomotion. These modes are described below;
- Plantigrade: In this mode of locomotion the mammals used to walk on their soles with palm, wrist, and digits all land to rest more or less on the ground, such as monkeys, apes, man, and bear, etc.
- Digitigrade: Some mammals tend to walk on their digits only. They run faster than plantigrade animals. In these mammals, the first digit usually reduces or completely lost as in rabbits, rodents.
- Unguligrade: These mammals walk on the tips of toes modified into hoof as deer, goat. This is the swiftest type of locomotion.