Although their differences are certainly substantial (e.g., sharks are cold-blooded and dolphins are warm-blooded), sharks and dolphins have some undeniable similarities: side fins, a dorsal fin, and a torpedo-shaped body. These similarities are analogies — traits the two lineages evolved independently as adaptations for moving swiftly in the water. Sharks were gliding through the oceans long before dolphins descended from land-dwelling mammals. Dolphins evolved flippers, a dorsal fin, and a torpedo-shaped body as natural selection shaped them for the life of an ocean predator.