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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