What are the similarities between frog, crocodile and hippopotamus? Explain why these similarities arose?

Crocodile, frog and hippopotamus, despite the fact that they seem completely different, have several similarities:

they have a streamlined body to better swim in water;
in these animals, the nostrils and eyes are located on a hill in order to look at what is happening, sticking their head out of the water.

The similarities arose because they live in the same conditions: mainly in water, but they cannot breathe in water, they often come to the surface.