Evolutionary changes in arrangement of bones in birds | class 12

Aslam o alikum I am Hassam ur Rahman and I am teaching Fsc biology since 2014 .I am always trying to improve myself and provide best lecture to students.i am taking content for the lecture from authentic and relevant sources but human errors are possible . you are requested to please highlight the mistakes.My lectures are equally reliable for Fsc and mdcat students #visiblescience #mdcatbiology #alevelbiology #neetbiology #fscbiology This lecture is about Evloutionary changes in the arrangement of bones and related mode of locomotion in major groups of vertebrates All vertebrates have a common body plan and have skeleton formed of the same basic parts, but there are many differences. Some of these can be related to changes in habitat for example, support and locomotion in sea requires adaptations which differ from those needed on land or in air. Most fishes are propelled forward by means of muscle contraction which pass along the body from anterior to posterior producing a characteristic S-band locomotion. Alternate contractions on both side produce lashing movements which drive the fish forward through the water. This type of motion is seen in cartilaginous fish like dog fish and sharks. Most land vertebrates are tetrapods. In four footed amphibians and reptiles, the legs emerged from the sides of the body and the S-wriggle is retained as a part of the body. Girdles and limbs of tetrapods show clear cut homologies in fundamental structure. The tetrapod pelvic girdle is united firmly to the sacral region of the vertebral column. It is composed on each side of three cartilaginous bones ilium, ischium, pubis. A depression, the acetabulum usually located at the point of junction of three bones, furnishes the articular surface for the femur. The limbs of tetrapods are fundamentally similar, fore and hind-limbs are also alike. The tetrapod limb is primitively pentadactyle. Reduction and fusion accounts for many variations from the primitive condition that are encountered. For example in the case of mammalian locomotion the legs project beneath the body providing more effective support. In running mammal, 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 pterodactyls, birds and bats. It involves far more muscular effort than swimming and walking or running. To generate sufficient lift to remain air-borne a flying organism must have wings with a large surface area in contact with the air and must beat its wings powerfully. The skeleton of birds is highly modified for flight. Among the more obvious adaptations are the enlargements of the pectoral girdle and the development of sternum to form a massive keel for the attachment of flight muscles. The supra-coracoid muscles provide power for tlhe upward stroke. The lifting action is possible because the tendon of the supra- coracoid muscles passes through an opening the formen 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. The shape of the wings greatly influences the speed and the type of flight which can be achieved. For example long narrow wings like those of gulls and other sea birds are ideal for gliding into wind. While short broad wings like those of many garden birds are effective for slow flapping flight. Bats have a quite different arrangement of wing bones but show a parallel range of adaptation for flight.