No one can explain how a whale or dolphin evolved because they didn't. A credible theory can't even be made how they did evolve.
How did the duckbilled platypuss evolve? Got any answers. Or will the 10,000 year answer be it?
The Duckbill Platypus
The explorer who first saw a hide of the duckbill platypus thought that it was composed of the hides of several different animals sewn together as a joke. Later, when a preserved specimen was brought to him for dissection, he finally declared it outrageous, but genuine! × It lays eggs, yet suckles its young.
× It has a ducklike bill, which has built within it a heat sensitive worm finding radar.
× Its tail is flat like a beaver's, yet furry.
× It has webbed feet in front, clawed feet in the rear.
× The reproductive systems are uniquely different from the rest of the animal world, but mostly mammalian in nature.
× The only other known monotreme, or egg-laying mammal is echidna or spiny anteater. Except for the fact that it lays eggs, it is about as different as you can get from the platypus.
Can you imagine what a pre-platypus might have looked like? Nothing in the fossil record gives us a clue about the origin of this animal, which is an outrage to evolutionists. This animal does very well in its natural environment in spite of its unusual features. To look at it, it would appear that this animal was pieced together from a variety of completely different animals.