Tetrapoda: Aves NEET Notes | EduRev

Biology Class 11

NEET : Tetrapoda: Aves NEET Notes | EduRev

The document Tetrapoda: Aves NEET Notes | EduRev is a part of the NEET Course Biology Class 11.
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Originated at the end of Jurassic period of Mesozoic era & advancement took place in cretaceous

Study of birds is known as ‘‘Ornithology’’

Dr. Salim Ali was the great ornithologist of India and known as ‘‘Birdman of India’’

Study of bird's egg is known as Oology.

Study of bird's Nest is known as Nidology.

Birds are glorified reptiles stated by Huxley.

Arrangement of wings on the body of bird is known as Pterylosis.

Body is boat-shaped. It is divided into head, neck, trunk and tail. Neck is long and flexible.

A cover of soft feathers (derivative of stratum corneum) is present all over the body, that is called ‘‘plumage’’

Scales are found only on hind limbs. 

Birds are warm blooded or Homeothermic or endothermic animals i.e. Body temperature remains almost constant.

  • Skin is dry and without glands. But oil glands or Preen glands are found on tail or Uropygium. These glands secrete oil, which makes feathers soft and waterproof.

–    Two pairs of limbs are present. Birds are feathered bipeds.

–    Forelimbs (with three digits) are modified into wings, which help in flying.

–    Four clawed digits are found on hind limbs. these are best adapted for perching, for walking on land, or for swimming in water.

  • Oesophagus is modified into Crop for quick food ingestion and storage and Gizzard for crushing the food which is swallowed unmasticated. Pigeon milk is secreted by both sexes (Crop product).


–    Gall bladder is absent.

A three chambered cloaca is present in the birds.

Teeth are absent in jaws. Jaws are modified into horny beak. Beak is toothless. An epidermal horny sheath is present on beak, which is called Ramphotheca.

Spongy lungs are present for respiration. Air sacs are also found attached to lungs forming accessory resp. organs these help in flying.

Sound producing organ at the junction of trachea and bronchi of birds is called syrinx.

Heart is four chambered.

Hepatic portal system is well developed in birds, but renal portal system is vestigeal developed. Sinus venosus absent. Only Right aortic arch persist.

R.B.Cs are nucleated, small and oval. No. of RBC/mm3 is max. in among animals.

Endoskeleton is bony. These bones are hollow, are is filled, and are called pneumatic bones. These make the body light in weight and help in flying.

Skull monocondylic.

Centrum of the vertebra is heterocoelous. (Saddle - Shaped)

Some vertebrae of the posterior body portion join together to form synsacrum

Last four caudal vertebrae fuse to form pygostyle.

Sternum is large. Swollen basal part of sternum is called ‘‘Keel’’ This keel offers a joint plane for flight muscles.

Keel is highly developed in flying birds.

Ribs of birds are bifid and uncinate processes are present in ribs.

Exoskeleton is in the form of soft feathers all over the body (except hind limbs)

Foramen of triosseus is found in their pectoral girdle.

Two bones, clavicle and interclavicle fuse to form V - shaped furcula or wish bone or Merry thought bone. Act as a spring between two girdles .

Furcula is absent in flight less birds.

Kidneys metanephric (Trilobbed). Ureters open into cloaca.

Members are always Uricotelic.

Uric acid is a semisolid substance. Excreta of marine birds is known as guano.

Most of the birds do not have urinary bladder.

Brain is large, smooth, highly developed. Cerebellum is well developed for aerial mode of life.

Cranial nerves are 12 - Pairs.

The skin around the nostrils is sensory in birds, that is called ‘‘Cere’’.

Eyes are large and well developed which are surrounded by rings made up of bony plates known as Sclerotic ossicles.

Eyes are large and nictitating membrane is present. Vision is monocular.

A specific comb like structure Pecten is found in the eyes of all birds except kiwi's eyes. Pecten helps in Acomodation of eye and provides nutrition of eye balls . It also control pressure of liquid present in  eye. Acute and Telescopic vision of birds is due to pecten.

External ears are present but ear pinnae are absent. Columella bone (Stapes) (one ossicle) is found in middle ear. Cochlea (not coiled) is present in internal ear.

Olfactory organs are less - developed.

Birds are monodelphic i.e. only left ovary and left oviduct is functional in females.

Birds are unisexual. Sexual dimorphism is well marked. Copulatory organ absent in males.

Fertilization is internal, oviparous. Eggs are large, megalecithal, telolecithal and cleidoic. Shell is perforated. Cleavage is meroblastic and discoidal.

Embryonic development is direct. Birds are included under group amniota. 

Parental care is well marked. Young one without feather is known as Nidiculous and with feather is known as Nidifugous.


Subclass - Archaeornithes

– Primitive ‘‘Reptile like birds’’ are included in this subclass, which belong to Jurassic period. All the members have becomes extinct.

– Wings are ill developed, i.e. capacity of flying was very less.

– Pygostyle was absent.

– Keel on sternum was absent.

– There were present 3 - 3 clawed digits of forelimb at the free edges of wings.

– Uncinate processes on ribs were absent.

– Teeth were present in the jaws of skull.

– All the members of this sub-class are the connecting links between reptiles and birds.

–    Archaeopteryx lithographica - Lizard bird. (Extinct in Cretaceous period) Its fossil was discovered by Andreas wagner in 1861 from Bavaria (Germany).

–    Archaeornis


Sub class - Neornithes

– This includes living as well as extinct birds of post jurassic period.

– Wings are well developed which are used in flying (except some birds)

– Last few vertebrae fuse to form pygostyle.

– Sternum is bigger and with keel.

– Digits of forelimbs are fused and claws absent.

– Thoracic ribs are having uncinate processes.

– Except some species (which are extinct) rest of the birds are toothless.

– In living members of this subclass, vertebrae are heterocoelous.

–    Last few vertebrae joins to form pygostyle.

–    This subclass is classified under four super orders.


Super order - Odontognathae :-

– These extinct birds were having teeth.

– Pygostyle was absent.

– Keel in sternum is absent

–    Hesperornis  (Flightless marine bird)

cthyornis  (Flightless marine bird)


Super order - Palaeognathae or Ratitae   

– It includes large and massive birds, which are flightless in nature.

These are able to run fast. Wings are reduced/rudimentary/vestigeal or absent.

– Caudal vertebrae are free and pygostyle is absent.

– Sternum is raft like which lacks Keel.

– Uncinate processes on ribs, Oil glands or preen glands and sound producing organ syrinx is absent.

–    StruthioAfrican ostrich or Camel-bird - It is the largest living bird of modern period. Polygamous, male incubate the eggs (Largest egg). In this bird urinary bladder and penis is present.

–    Rhea - South american ostrich :- It also has urinary - bladder and penis.

–    Apteryx -  Kiwi - It is National bird of New zealand. It has hair like feathers all over its body. It is smallest flightless bird.

–    Dromaeus - Emu - It is a monogamous bird in which only males look after their young ones and eggs.

–    Aepyornis - Elephant bird

–    Casuarius - Cassowary (found in New Guinea/Australia)


Super order - Impennae

– All are  aquatic birds

– forelimbs are modified into flippers

– Limbs are webbed.

– Teeth are absent

– Sternum without keel.

–  Spheniscus - Penguin - It is also called ‘‘sea bird of Antarctica’’ (Emperor Penguin)

–   Aptenodytes - Penguin


Super order - Neognathae or Carinatae

– This super order includes flight birds of modern era. Wings are well developed

– Pygostyle is present

– Keel in sternum is highly developed.

– Its crop glands secrete pigeon milk

– Uncintate processes at ribs are well marked.

– Oil glands or preenglands are found.

– Toothless beak

– Sound producing syrinx is present.

–    Pavo - cristatusPeacock       -           It is the national bird of India.

–    Psittacula krameri      -  Indian parrot. (upper jaw movable - Psittaciformes)             

–  Columba livia-  Blue rock pigeon its crop glands secrete pigeon milk (columbiformes)

–    Streptopelia                     -           Dove

–    Passer domesticus        -           Sparrow - It shows commonsalism with man.

–    Corvus splendens          -           Crow

–    Molpaster                         -           Bulbul

–    Cygnus                               -           Swan - Aquatic bird having webbed limbs

–    Bubo bubo                        -           Bubo or owl or ‘‘III of oman’’

–    Cuckoo                               -           It lays its eggs in the nest of other birds (Crow)

–    Eudynamis                        -           Indian Koel (Nest - Parasitism)

–    Anas                                    -           Duck

–    Phoenicopterus               -           Flamingo

–    Alcedo                                 -           King fisher

–    Raphus didus                    -           Dodo (Mauritian extinct bird in 17th centuary)

–    Dinopium                           -           Wood pecker - Kathphorva

–    Diomedea        -     Albatross - Marine bird with largest wings in flying birds.

–    Milvus                                     -           Kite (Predatory birds)

–    Falcon                                     -           Falcon (Predatory birds)

–    Neophron                                -           Vulture (Scavenger bird)

–    Choriotis-nigriceps state  -    Great Indian bustard. It is also called Gondavan. It is the bird of Rajasthan. (local name - Godavan)

–    Helena       -           Humming bird - It is also called sunbird. It feeds on nector of flowers it is the smallest bird. It is found in cuba. It can fly in forward and backward both the directions. It can fly like helicopter. Its size is about 3 to 4 cm. 

–    Ploceous                                -           Weaver bird (Baya)

–  Micropodus - Pitohiudicthous/pathua - It is the only poisonous bird, which is found in Newguinea.

–    Swift spine tailed                    -           Fastest flying bird, it is found in Japan.

– Poor bill - Bird which shows sleeping stage and undergoes hibernation. Migratory Birds (Phenolosy = Study or bird migration)

–    Pluvialis dominica - It is an American bird which migrates from south to north and from north to south.

–    Scolopax eusticoa - It migrates from hill area to planes.

–    Himalyan partiges - It can fly over 6000 miles

Sterna parasisaea - Champion bird - Arctic to Antarctic and back.



There are different types of feather namely

(1) Quill (flight feather) consists of (a) Remiges - feather of wings (b) Retrices - feather of tail

(2) Coverts - small just like quill for filling gap on wings & tail.

(3) Contours - small feather to cover the body

(4) Filoplums - Beneath the contours 

(5)  Down feather - Cover the body of newly hatched bird. (Filoplume and Down feather make body surface as heat - resistant.)

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