We humans live from the sea. For example, we eat fish and crustaceans, but we also use the sea for our ships. Some sea creatures are a lot like us: sea mammals...
Humans are Mammals: This means that, as a baby, we drink milk from our mothers.
Sea mammals nurse their young too, but they live in the sea. The best known sea mammals are dolphins and porpoises.
Many people mistake porpoises for dolphins and vice versa.
But there are very clear differences between the two.
One clear difference is in the shape of their dorsal fin:
That of the dolphin looks like a sickle or crescent, while that of the porpoise looks more like a triangle.