So—what do we have above? Two pictures of dolphins?

Nope, we have an ancient reptile from the age of dinosaurs and a modern dolphin. This is an example of convergent evolution. Or you could call it “form follows function.” Both creatures look like fish superficially but are, of course, very different inside, one a mammal one a reptile and and neither are like fish which was the first vertebrate group to evolve.

Trivial differences: a fish propels itself by moving its tail from side to side, a dolphin or whale by moving it up and down—we have all seen video of a whale slapping its tail down on the surface of the water.

Rabbits and Hares are a separate species, they cannot interbreed

We have seen another case of convergent evolution: the Tasmanian Tiger is a marsupial dog.