Nov 30, 2014

Evolutionary changes in vertebrate bone arrangement

The arrangement of bones and mode of locomotion have undergone significant evolutionary changes in major groups of vertebrates over time. These changes are a result of adaptations that have allowed animals to better survive and thrive in their environments, and have contributed to the diversity of vertebrate life on Earth.

One of the most significant changes in bone arrangement and locomotion is the transition from fish to tetrapods (four-limbed vertebrates), which occurred around 400 million years ago. This transition involved the development of limbs that could support the weight of the animal on land, as well as changes in the arrangement of bones in the skull and jaw that allowed for a greater range of movement and feeding options.

Within the group of tetrapods, there have been numerous additional adaptations and changes in bone arrangement and locomotion. For example, the evolution of flight in birds involved the development of lightweight, fused bones and modifications to the wings and feathers that allowed for powered flight. Similarly, the evolution of four-legged mammals involved changes in the arrangement of bones in the limb and spine, as well as modifications to the feet and claws that allowed for different modes of locomotion such as running, climbing, and digging.

Fish

They swim by undulating their body from side to side. The undulating movements were produced by alternative waves of contractions passing along the either side of the animal- These undulations were transmitted through the posterior part of the body and tail as a powerful backward pushes against the dense water. The back bone is flexible and generally vertebrae are not interlocked for undulating movement.

Tetrapods

Most vertebrates are tetrapod. In the amphibian and reptiles the legs emerged from the sides of the body and S- wriggle (to twist to and fro in S shape) is retained as a part of the body. The girdles and limbs of tetrapods show clear cut homologies in fundamental structure. The pelvic girdle is united firmly to the sacral region of the vertebral column. It consists of ilium, ischium and pubis which are cartilaginous. Femur is articulated at the acetabulum. Forelimb is pentadactyle, showing many primitive conditions. For example in mammals the legs project beneath the body providing more effective support.

In running mammals, stride length and power are increased by arching the spine first upward with the limbs fully extended... in this way the force produced by the back muscle is transmitted to ground.

Flight has evolved in three types of vertebrates namely in pterodactyl (flying dinosaurs-reptiles), birds and bats. It involves for more muscular effort than swimming and walking or running. The bones show flying adaptations i.e., pectoral girdle is enlarged, sternum forms keel for the attachment of muscles. The pectoral muscles provide power for the upward stroke. The lifting action is due to the tendon of the supra-coracoid muscles which passes through an opening the foramen triosseum formed between the scapula, coracoid and clavicle bones and is attached to the upper surface of the humerus.

The number of bones is reduced as compared to those in the limbs of other vertebrates and many bones are fused together to increase strength. Generally the fast flying birds have a smaller wing are& and a large span, while slower flying birds have shorter, wider wings e.g. many garden birds. Long narrow wings like those of gulls and other sea birds are ideal for gliding into wind. In walking, the posture of the bird brings the center of gravity of the bird below the joint of the femur and pelvis...

Bats have a quite different arrangement of wing bones but show a parallel range of adaptation for flight.

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