We classify living organisms by their shared characteristcs.
Some characteristcis like feathers are unique to a group whilst others who have a backbone are common to several groups.
Animals with backbones are called vertebrates. There are 5 groups:
Fish- excahnge oxygen and carbon dioxide across gills and lay eggs that are ferilised internally.
Amphibians- Exchange gases through their skin and lay externally fertislised eggs.
Reptiles- exchange gases via their lungs and lay internally fertilised eggs.
Mammals- give birth to live young which grow inside the body of the mother. Eggs are fertilised…