Here's a breakdown:
* Sharks belong to a group called Chondrichthyes, which means "cartilage fish". They are more closely related to rays than to bony fish. They evolved from a common ancestor with bony fish around 450 million years ago.
* Dolphins belong to the order Cetacea, which includes whales and porpoises. They are mammals and evolved from land-dwelling mammals around 50 million years ago.
So, while both sharks and dolphins live in the ocean, they developed their aquatic lifestyle independently from different ancestors. This is an example of convergent evolution, where unrelated organisms evolve similar features due to adapting to similar environments.