Explain how animals in Vertebrata are classified into further subgroups?

The major characteristics used to classify animals in Vertebrata are: 1. The kind of exoskeleton or endoskeleton. 2. The kind of respiratory organs. 3. The method of reproduction and giving birth to young ones. On the basis of above mentioned characters the vertebrata is divided into following classes.
1 Exoskeleton of scales: Endoskeleton of cartilage or bones; breathing through gills – pisces (fishes).
2. Breathing through gills only in larva ; skin slimy – Amphibia
3. Exoskeleton of scales or scutes ;laying eggs outside the water – Reptilia.
4. Exoskeieton of feathers; lays eggs ; flight possible – Aves (birds).
5. Exoskeleton of hair; external ears, ; give birth to young ones – Mammalia.