Aves General Characteristics, Classification and Examples

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Aves General Characteristics

All types of birds are included in this class
Body is boat shaped. It is divided into head, neck, trunk and tail
Warm blooded or homeotherms
Exoskeleton is made up of feathers, scales, claws on legs and beak
Limbs are two pairs, fore limbs are modified into wings for flying and hind limbs are modified for walking, running, swimming and perching
Skin dry without glands, only preen gland is present at the base of tail
Bones are pneumatic or hollow and have no bone marrow
Digestive system has additional chambers, the crop and gizzard. Oesophagus is modified into crop for quick food ingestion and storage and gizzard for crushing the food which is swallowed unmasticated.
Respiration by lungs, air sacs are also found
Sound producing organ at the junction of trachea is called syrinx
Excretion uricotelic and urinary bladder absent. cloaca present
Brain is large and highly developed. cranial nerves are 12 pairs
Unisexual, sexual dimorphism present and oviparous.
Copulatory organ absent in males. In female left ovary is well developed
Eggs are megalacithal and cleidoic.
All the birds form nest. migration and parental care is well marked.

The class Aves is divided into two Subclass: Archiornithes and Neornithes

Order – Archaeopterygiformes

So far two genera have been described, each with a single species from the upper Jurassic lime stones of Solenhofen in Bavaria.

Forelimbs bear remiges.
Tail long with many vertebrae, which gradually taper to the distal end. The rectrices are arranged in two lateral rows on each side of the caudal vertebrae.
The carpals and metacarpals free and hand with three clawed digits.
The eyes were large.
The skull proportionately large, with a rounded bird-like brain case and strong jaws, in each of which hearing a series of conical teeth lodged in socket.
Enamelled crowned teeth on both the jaws.
The sacrum made up of only about six vertebrae.
The cervical and thoracic ribs probably devoid of uncinates. Thin abdominal ribs or gastralia or so-called ventral ribs were on ventral wall of abdomen.
The cerebral hemispheres smooth, long and narrow and cerebellum small.
Examples: Archaeopteryx lithographica, Archaeornis siemensi.

Includes live and extinct birds
Wings well developed
Bones pneumatic
Toothless beak
Tail small and claws absent on forelimbs
This subclass divided into 4 superorder:- Odontognathae, Palaeognathae, Impennae and Neognathae

Superorder 1. Odontognathae

Superorder 2. Palaeognathae

Large-sized flightless birds, descended from Volant ancestors at the end of the Mesozoic period.
The feathers are primitive, without hooked barbules. Barbs remain free. Apterae are usually absent in adult. The rectrices are absent or irregularly arranged.
The wings reduced in size or vestigeal or absent.
Pygostyle small or undeveloped.
The sternum is flat, raft-like. The coracoid and scapula are comparatively small and completely ankylosed.
The coracoscapular angle approaches to right angle and the acrocoracoid process is vestigeal.
Large basipterygoid process developed from the basisphenoid. The vomer is large and broad and separates the palatines; which do not come in contact with the cranium.
The quadrate articulates with the skull by a single or partially divided facets.
The males are with erectile penis and the females have clitoris. The young are precocious.
Examples: Struthio (Ostrich), Rhea (American Ostrich), Apteryx (Kiwi), Dryomaeus (Emu) and Casuarius (Cassowary) etc.

Superorder 3. Impennae

Evolved from ancestors having wings used for both swimming and flight and gradually changed to form an effective paddle for swimming.
Body sleek, streamlined, and offers least possible resistance to diving and submarine activities.
Closely packed plumage; feathers small, scale-like, dense, over entire body without apteria.
Hind limbs modified for swimming; metatarsal, unlike those of other birds only partly fused. The feet are strongly webbed.
The integument is provided with, thick, fatty, insulating layer.
The bones, excluding certain skull bones, are solid. Air sacs absent.
The bones of featherless wings flattened and united to form a powerful, resistant paddle or flipper moving only at the shoulder joint.
Monogamous and one egg is laid at a time. Feed on fishes, crustaceans, squids, etc.
Examples: Aptenodytes, Pygoscelis, Eudyptes, Eudyptula, Spheniscus, etc.

Superorder 4. Neognathae

Modern birds with well-developed wings, keeled sternum, and fully adapted for flight.
Beaks without teeth.
Slender vomer separates the palatines imperfectly.
The palatines are protruded posteriorly and in contact with the base of cranium and remain movably articulated with small pterygoids.
Tail vertebrae 5 or 6. Pygostyle absent.
Forelimbs with metacarpals joined, and fingers included in wings.
Examples: Pavo cristatus (peacock), Psittacula (indian parrot), Columba livea (blue rock pigeon), Passer domesticus (sparrow), Corus splendens (crow), Helina (humming bird), Diomedea (albatross), Neophron (vulture), Bobo (owl) and Swift (fastest flying bird)

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