Spot the Differences

Sharks and dolphins both live in the ocean. What is the same about them? What is different?
Shark

A shark is a type of fish. It breathes underwater with gills. Sharks sometimes travel and hunt alone. A group of sharks is called a school.
Dolphin

A dolphin is a mammal. It rises to the surface to breathe air into its lungs. Dolphins travel and hunt in groups. A dolphin group is called a pod.