Question

What are the general characteristics of members of class aves?

Answer 1

All birds are grouped under the class aves. This is the fourth class of Phylum Chordata and are said to be descended from reptiles.

Complete answer:
Birds have the following general characteristics:
-They perform homeostasis as they are warm-blooded animals.
-They have specialised limbs as their forelimbs are modified into feathered wings which help in flight along with well developed flight muscles. Their hindlimbs are structured as such to help in walking, hopping, perching, swimming, grasping, etc.
-They have scaly legs indicating their reptilian ancestry.
-Birds have pneumatic or hollow bones, meaning that the endoskeletal bones in a bird are devoid of bone marrow. This hollowness assists in flight as it reduces weight at a great extent.
-For efficient flying, their bodies are stream-lined to minimize the air resistance and feathers on their body provide appropriate air passage. Feathers prevent heat loss too.
-Their jaws are developed into a bony beak which lacks teeth.
-They have excellent eyesight to help them hunt on small terrestrial prey from the skies.
-Their digestive tract consists of 2 main organs, Crop and Gizzard, used to soften and grind food respectively.
-Syrinx is the voice box of birds found at the base of trachea.
-Their lungs are spongy and elastic for easy respiration.
-They have a four-chambered heart.
-They possess oval, nucleated and biconvex RBCs.
-Nervous system consists of 12 pairs of cranial nerves.
-Female birds have a single ovary and oviduct placed on the left side in their body.
-Birds show sexual dimorphism, i.e. male and female have distinct features.
-They are oviparous and their eggs have 4 embryonic membranes; amnion, chorion, allantois and yolk sac.
-They lack all skin glands except oil glands.
-They may be herbivorous or carnivorous.

Note:
There are two classified groups in aves; Archaeornithes and Neornithes. The former group contains birds that are now extinct, for example Archeopteryx. They looked more like reptiles as they had toothed beaks and long tails.
Neornithes are the birds we see today, toothless and short tailed. Some extinct birds belong to this group too.