Page 1 :
CLASS AVES : CHARACTERS,, CLASSIFICATION AND EXAMPLES, SUB-PHYLUM-, VERTEBRATA, - GNATHOSTOMATA, SUPER-CLASS - TETRAPODA, CLASS - AVES, Class Aves includes the birds, flying vertebrates characterized by an exoskeleton of feathers, ana resting on ground on two hind limbs only. These are commonly called "glorified reptiles" as, these share a number of features with the reptiles, their ancestors. Class Aves includes about 9,000, living species of birds., CHARACTERS, 1. Body shape. Body is boat-shaped and streamlined to reduce resistance in air during flight., Body is divided into four parts : Head, neck (long sized), trunk and tail (very reduced)., 2. Skin and Exoskeleton. Skin is dry and non-glandular except oil or preening or Uropygeal, gland on tail and is further covered by a feathery-exoskeleton which insulates body and conserves, 2ody heat., 3. Limbs. These have two pairs of pentadactyl limbs. Fore limbs are modified into wings., These are feathered-bipeds (locomotion on land on two hind limbs). Fingers are generally three, and without claws. Hind limbs are modified for perching (e.g. owls), or walking (e.g. pigeon) or, cunning (e.g. ostrich) or swimming (e.g. cormorant).Toes generally have claws and, Hallux backwvard and 3 toes forward)., in number, 4. Endoskeleton. It is mainly formed of bones. Skull is monocondylic. Long bones are, pneumatic (with air cavities) to provide lightness. Atlas and Axis both are present. Sacral vertebrae, are many and fuse to form sacrum to support ilia. Posterior caudal vertebrae are fused to form, pygostyle to support tail feathers called rectrices. Vertebrae are heterocoelous. Ribs are double, headed and with uncinate processes to form a thoracic basket to protect heart and lungs. Sternum, 'chest bone) is keeled except flightless birds. Tibiotarsus (tibia + tarsals) and tarsometatarsus, (tarsais + metatarsals) are formed in hind limbs. Pectoral girdle is with a V-shaped furcula or wish, bone or merry thought (2 clavicles joined to an interclavicle)., 5. Digestive system. Mouth is always bounded by a beak covered by a horny sheath, rhamphotheca., Birds are edentulous (no teeth). Food-storing crop and food masticating gizzard are present. Alimen-, iary canal opens out by cloacal aperture. Cloaca is 3-chambered for conservation of water., 6. Respiratory system. Birds show only pulmonary respiration (with lungs). Lungs have air, sacs which help in double respiration and also act as internal cooling agents. Sound producing, organ is syrinx (at the base of trachea)., 7. Circulatory system. Heart is proportionately large sized. It is 4-chambered (two auricles, and two ventricles). Bicuspid valve is fully formed between left auricle and left ventricle but, tricuspid valve is not formed. RBCS are oval, biconvex and nucleated. Both the accessory chambers, are absent. Sinus venosus has merged in right auricle while conus arteriosus is divided into two, arches : pulmonary arch and right systemic arch. Renal portal system is vestigial in birds., 7る, Scanned by CamScanner

Page 2 :
8. Nervous system. Brain is rounded and large-sized in proportion to body size and has, 12 pairs of cranial nerves. Optic lobes (sight) and cerebellum (equilibrium) are large-sized as these, are more dependent upon sight and equilibrium, while olfactory lobes are small-sized as these are, less dependent upon smell., 9. Sense organs. Internal car has cochlea with organ of Corti but is not coiled. There is single, ear-ossicle (stapes) in middle ear. Nasal chamber have turbinals or chonchae and internal nares, open in the posterior part of buccal cavity. Thcse are adapted for air conditioning., 10. Excretory system. Excretory organs are kidneys. Kidneys are metanephros and, retroperitoneal. Each kidney is trilobed. Excretion is uricotelic. Urinary bladder is absent. Ureters, open in cloaca., 11. Reproductive system and Development. Sexes are unisexual and generally show sexual-, dimorphism. Ferilization is internal. Female always oviparous. Testes are paired. Right ovary and, oviduct are lost or vestigial in female. Gonoducts also open in cloaca. Egg is polylecithal, cledoic, and shelled. Cleavage is meroblastic and superficial. Embryonic membranes (e.g. amnion) are, formed during development. Young.is either nidifugous or precocial (feathered, able to walk and, feed e.g. fowls) or nidiculous or altricial (naked, helpless and dependent e.g. sparrow, dove, etc.)., 12. Body temperature. These are homeothermal or warm-blooded (constant body tempera-, ture) animals., It includes about 9,000 living species of birds. Archaeopteryx (flying lizard) of Jurassic period, is earliest known extinct bird. It suggest that birds are glorified reptiles., CROW, PSITTACULA, Male and Female, EUDYNAMIS, .COMB, CLAWS, WATTLE-, EAR LAPPET, CATTLE EGRET, MALE, SPUR, Female, Male, GALLUS, -TAIL, NEOPHRON, FEATHERS, PAVO, ANAS, The Great Indian, BUSTARD, WING, FEATHERS, TYTO, COLUMBA LIVIA, TAIL, MILVUS, FEATHERS, Flying Birds. 4, Scanned by CamScanner