Class Aves - NEET-Biology

 Class Aves

Fig: Pigeon (Columba livia domestica)

Aves is the name of the class to which birds belong in taxonomy.

Important characteristics:

•  The body usually spindle-shaped, with four divisions: head, neck, trunk, and tail.

• Skin is dry without glands except the oil or preen gland at the base of the tail.

• Many of the characters of the birds are adaptations that facilitate flight.

• A bird's most obvious adaptations for flight are its wings & feathers.

• The forelimbs are modified into wings. Epidermis covered with feathers.

• The presence of feathers is the most characteristics feature of aves.

• Fully ossified endoskeleton & the long bones are hollow with air cavities (pneumatic).

• Respiration is by the lungs. The circulatory system consists of a four-chambered heart with two atria & two-ventricles; nucleated erythrocytes. Livings birds are also toothless.

• They are warm-blooded animals, i.e. they are able to maintain constant body temperature.

• The excretory system included metanephric kidneys; ureters open into cloaca; no urinary bladder; uric acid main nitrogenous waste.

• Sexes separate; females have left ovary & oviduct only; copulatory organ (penis) only in ducks, geese, paleognaths & a few others.

• Sexes are separate. Fertilization is internal.

• They are oviparous & development is direct. Amniotic eggs with much yolk & hard, calcareous shells; embryonic membranes are present in the egg during development.

• Example: Corvus (crow), Columba (pigeon), Psittacula (Parrot), Struthio (Ostrich), Pavo (Peacock), Neophron (Vulture).

• Flightless birds: Struthio camelus (African ostrich), Rhea americana (South America ostrich), Dromaius novaehollandiae (Australian emu).

Fig: Dromaius novaehollandiae