Well, squirtle and blastoise are similar things.
Mammals didn't exist for a time, according to you. There were reptiles, fish, insects, trilobites, etc. But no mammals.
So, scales evolved into hair somehow? And breasts evolved from nothing? And, laying eggs somehow evolved into internal fertilization?
Warning - while you were typing 4 new replies have been posted. You may wish to review your post.
Oh my...
Yes. You got it. All those adaptions were made because they were necessary to the particular mammals survival. Scales to hair, to keep the heat in, in cold environments.
We evolved our loveual organs for multiple reasons, I'm guessing. It's more convenient to keep your young in your stomach until their born than sit in the same place and have fears of them getting eaten.