NEET Biology Animal Kingdom Notes - Class-Aves

 

Class Aves

 

Class Aves.

 

            (i) General Characters

            (1) Feather-clad, air-breathing, warm-blooded, oviparous, bipedal flying vertebrates.

(2) Limbs are two pairs. Forelimbs are modified as wings for flying. Hind limbs or legs are large, and variously adapted for walking, running scratching, perching, food capturing, swimming or wading, etc.

            (3) Exoskeleton is epidermal and horny.

            (4) Skin is dry and devoid of glands except the oil or preen gland at the root of tail.

            (5) Pectoral muscles of flight are well developed.        

(6) Skull smooth and monocondylic, bearing a single occipital condyle. Cranium large and dome-like. Sutures indistinct.

            (7) Vertebral column short. Centra of vertebrae heterocoelous (saddle-shaped).

            (8) Sternum large, usually with a vertical, mid ventral keel for attachment of large flight muscles.

            (9) Ribs double-headed (bicephalous) and bear posteriorly directed uncinate processes.

            (10) Both clavicles and single inter clavicle fused to form a V?shaped bone, called furcula wishbone.

(11) Heart completely 4?chambered. There are neither sinus venosus or truncus arteriosus. Only right aortic (systemic) arch persists adult. Renal portal system vestigial. Blood corpuscles nucleated.

            (12) Birds are the first vertebrates to have was blood. Body temperature is regular (homoiothermous).

            (13) Respiration by compact, spongy, distensible lungs continuous with thin air-sacs.

(14) Larynx without vocal cords. A sound box or syrinx, producing voice, lies at or near the junction of trachea and bronchi.

(15) Kidneys metanephric and 3?lobed. Uterus open into cloaca. Urinary bladder absent. Birds are urecotelic. Excretory substance of urates eliminated with faeces.        

            (16) Sexes separate. Sexual dimorphism of tern well marked.

            (17) Fertilization internal, preceded by copulation and courtship. Females oviparous.

(18) Eggs develop by external incubation. Cleavage discoidal, meroblastic. Development direct, Extra-embryonic membranes (amnion, chorion, allantois and yolk-sac) present.

            (19) Parental care is well marked.

(ii) Classification of Aves : Birds show less diversification than any other group of vertebrate animals. About 9,000 living species of birds are known at present. 25 to 30 avian orders are recognized depending on the taxonomist. Class Aves is first divided into two subclasses.

            (a) Sub-Class I. Archaeornithes : Gr., archios, ancient + ornithos, bird)

            (1) Extinct, archaic, Jurassic birds of Mesozoic Age, about 155 million years ago.

            (2) Wings primitive, with little power of flight.

            (3) Vertebrae amphicoelous.

            (4) Sternum without a keel.

            (5) Thoracic ribs slender, without unicinate processes. In Archacopteryx beak in toothed.

            This sub-classes includes a single order

Order Archaeopterygiformes : Example ? Archaeopteryx lithographica, from Jurassic or Bavaria, Germany; one specimen lying in the British museum, London, the other lying in the Berlin.

            (b) Sub-class II. Neornithes : (Gr., neos, modern+ ornithos, Birds)

            (1) Modern as well as extinct post-Jurassic birds.

            (2) Wings usually well-developed and adapted for flight, with few exceptions.

            (3) Teeth absent except in some fossil birds.

            (4) Vertebrae heterocoelous in living forms.

            (5) Sternum usually with a keel.

            (6) Thoracic ribs usually with uncinate processes.

            (7) Abdominal ribs absent

            This sub-class is divisible into 4 super-orders:

          Super-order 1. Odontognathae : (Gr., odontos, teeth)

            (1) Extinct, Upper Cretaceous birds.   

            (2) Jaws bear teeth, ?so advantageous for catching fish?.

          Order 1. Hesperornithiformes

            Example ? Hesperornis, Enaliornis, Baptornis, etc.,

            Order 2. Ichthyornithiformes

            Examples ? Ichthyornis, Apatornis.

          Super-order 2. Palaeognathae or Ratitae : (Gr., palaios old + gnathos jaw; L., ratis, raft).

            (1) Modern big-sized, flightless, running birds, without teeth.

            (2) Wings vestigial or rudimentary; feathers devoid of interlocking mechanism.

            (3) Rectrices absent or irregularly arranged.

            (4) Oil gland is absent, except in Tinamus and Kiwi.

(4) Skull is dromaeognathous or palaeognathous that is, vomer is large and broad and interpolated between palatines.

            (5) Sternal keel vestigial, absent or flat, raft-like.

            (6) Uncinate processes are vestigial or absent.

            (7) Clavicles are small or absent.

            (8) Pectoral muscles poorly developed.

            (9) Syrinx is absent

            The flightless birds or ratites are not represented in India. They are grouped in 7 orders as follows;

          Order 1. Struthioniformes : (Gr., struthio, ostrich + form)

            (1) Legs strongly developed, each with two toes (3rd and 4th) with stunted nails.

            (2) Pubes form a ventral symphysis.

            Examples ? True ostriches (Struthio camelus) of Africa and western Asia (Arabia)

          Order 2. Rheiformes : (Gr., Rhea, mother of Zeus + form)

Examples ? American ostriches or common rhea (Rhea americana) represented by two species in South American pampas; Darwin's rhea (Pteroncemia pennata).

            Order 3. Casuariformes

Examples? Cassowaries (Casuarius) of australia, and New Guinea and Emus (Dromaius novaehollandiae) of New Zealand

            Order 4. Apterygiformes

            Examples? Kiwis (Apteryx) or New Zealand.

          Order 5. Dinornithiformes

            Examples ? Moas (Dinornis maximus) of New Zealand

            Order 6. Aepyornithiformes

            Examples ?Giant Elephant-birds of Africa and Madagascar. Aepyornis titan, Mulleornis.

            Order 7. Tinamiformes

            Examples ? Tinamou (Tinamus), Eudromia

          Super-order 3. Impennae

          Order  1. Sphenisciformes

            Examples ? Penguins (Aptenodytes) Southern Hemisphere.

            (1) Most modern, usually small-sized. Flying birds.

            (2) Wings well-developed ; feathers with interlocking mechanism.

            (3) Rectrices present and arranged regularly.

            (4) Pterylae are regular.

            (5) Oil gland is present.

            (6) Skull is neognathous, that is, vomer is short allowing palatines to meet.

            (7) Sternum with a well-developed keel.

            (8) Uncinate processes are present.

            Pygostyle is present

Super order 4. Neognathae : The super-order Neognathae includes several orders. For the sake of study they may be grouped into at least 6 homogeneous ecological groups, as follows :

Group A. Arboreal Brids : Under this group may be placed the majority of birds spending most of their lives in and around shrubs and trees.

          Order 1. Passeriformes : (L., passer, sparrow + form)

This is the largest of all the bird orders including half the known species. Feet are adapted for perching, while beaks are adapted for cutting.

Examples : Common house sparrow (Passer domesticus), common house crow (Corvus splendens) common myna (Acridotheres ttristis)

Order 2. Piciformes : (L., picus, wood pecker + form) It includes woodpeckers, toucans, sap-suckers and their allies.

            Examples : Yellow fronted pied woodpecker (Dendrocopos mahrattensis).

            Order 3. Columbiformes : (L., columba, dove + form) It includes doves and pigeons

            Examples : Blue rock pigeon (Columba livia). Green pigeon (Crocopus), extinct dodo (Raphus)

            Order 4. Psittaciformes : (L., psitacus, parrot + form)

            It includes parrots, parakeets, cockatoos, macaws, love-birds, etc., denizens of the equatorial jungles.

            Examples : Large Indian parakeet (Psittacula eupatria), green parrot (psittacula krameri)

Group B. Terrestrial Brids : These birds are perfectly able to fly but spend most of their time walking or running on ground.

Order 5. Galliformes : (L., gallus, a cock + form)  It includes gamebrids notable for their palatability, massive scratching feet, short and powerful flight and largely graminivorous diet.

            Examples : Red jungle fowl (Gallus), peafowl (Pavo cristatus),

          Order 6. Cuculiformes : (L., cuculus, cuckoo + form) It includes cuckoos and their allies

Examples : Cuckoo (Cuculus canorus), Koel (Eudynamis scolopaeous), Crow-pheasant (Centropus sinensis)

          Group C. Swimming and Diving Birds

Order 7. Anseriformes : (L., anser, goose + form) Aquatic birds such as geese, swans and ducks belong to this order.

            Examples : Wild duck or mallard (anas), kcommon teal (nettion crecca), bar-headed goose (Anser indica)

          Order 8. Coraciiformes : (Gr., korax, crow or raven + form) It includes kingfishers and their allies.

            Examples : White breasted kingfisher (Halcyon smyrnensis), pied kingfisher (Ceryle rudis)

Order 9. Gaviformes : (L., gavia, sea mew = form) It includes marine birds, called loons (gavia) represented by only four species.

          Order 10. Podicipediformes or

Colymbiformes (Gr. kolymbos, diving bird) It includes grebes (Podicipes), often called divers because of their habits.

          Order 11. Procellariformes : (L., Procella, a tempest + form)

It includes tube-nosed, long and oily winged seabirds such as albatrosses (Diomedea), Petrels (Procellaria), shearwaters.

Order 12. Pelecaniformes : (L., pelicanus, pelican + form)  It includes pelicans, darters, gannets and cormorants.

            Examples : Pelicans (Pelecanus), little cormorant (Phalacrocorax niger)

          Group D. Shore Birds and Wading Birds

These aquatic birds seldom swim or dive beneath the water to any great extent.

Order 13. Charadriiformes : (NL., charadrius, genus of plovers + form) This order includes a rather diverse group of water frequenting shore birds characterized by long wading legs, webbed toes and mudprobing beaks.

            Examples : Red wattled lapwing (Lobivanellus indicus)

          Order 14. Ciconiiformes : (L., ciconia, a stork + form)

It includes long?legged, marshy wading birds with long snake-like neck and javelin or pincer-like beak for piercing their aquatic prey.

Examples : Cattle egret (Bubulcus ibis), heron (Ardea herodias), spoonbil (Platalea leucorodia), strok (Ciconia), flamingo (Phonicopterus).

Order 15. Gruiformes : (L., grus, crane + form) It includes crane-like wading birds with long legs and partially webbed feet.

            Examples : Common coot (Fulica atra),

          Group E. Birds of Prey

          Order 16. Falconiformes : (L., falco,falcon + form)

            The diumal birds of prey with sharp hooked beaks and strong curved claws.