What are the major evolutionary trends that developed among major vertebrate groups?

Specifically, those that allowed for the transition from aquatic to terrestrial life.

Many evolutionary changes resulted in the transition of aquatic vertebrates into terrestrial organisms. Some of these are:

Improved respiration

In terrestrial organisms, the respiratory system is more complex and enhanced than the aquatic vertebrates. For instance, the early amphibians had gills for respiration. But with the passage of time, lungs appeared which made life on land more feasible.

Body coverings

The formation of rigid and insulated body coverings also was an adaptation that emerged for making life feasible on land.

Development of limbs

Limbs allowed movement on land. With the passage of time, feet developed from the limbs.