The main adaptive features of this pigeon( Columba Livia) are associated with flight, with cleidoic development, and with homoiothermy.
Adaptation for flight is manifested in the following features__
- Many skeletal modifications especially the type of front-limb are found in columba livia, and the carina for accommodating the large flight muscle.
- The remiges and rectrices, both concerned with flight.
- Considerable reduction of weight by hollowing out of the bones and by the large air-sacs.
- Excellent respiratory and vascular systems.
- Very good vision.
- Remarkable muscular co-ordination is also an obvious feature in columba livia.
- Only at a high temperature is such strenuous activity possible for long periods.
In connexion with cleidoic development there are ____
- The large shelled eggs, generously provided with food.
- The allantois and other embryonic membrance.
- An insoluble nitrogenous end-product in this pidgeon( columba livia) which takes little storage space in the egg.
- Suppression of one ovary and one oviduct and lack of a public or ischial symphysis.
Concerned with homoiothermy, there are____
- The high rate of metabolism, necessitating frequent and large food supplies, efficient digestion and absorption, and rapid respiratory rate.
- The covering of feathers provides excellent insulation.
- The lack of glands in the skin prevents loss of heat by evaporation. Careful consideration will reveal a host of mirror modification which are adaptive.
Sub-phylum: Craniata [Vertebrata]
The Neornithes are distinguished from the Archaeornithes by the presence of a pygostyle at the end of a shortened tail, the possession of a carpo-metacarpus, and the arrangement of the rectriece in a semi-circle. Members of the order Columbiformes are distinguished from those of other orders by many small characteristics. Among them are the large crop, the small caeca and the vestigial vomer. Two families, the columbidae and the Raphidae belong to the order columbiformes, the former order being separated by the power of flight whereas the latter includes the dodo and solitaire, two extinct flightless birds. Birds in the genus Columba have twelve rectrices. The species are separated by small differences of colour, size, habitat and song.
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