Why is it more common to see two heads on some species like turtles or snake than it is to see a two headed shark or lion?

Question

Why is it more common to see two heads on some species like turtles or snake than it is to see a two headed shark or lion?

In: Biology

Answer 1

Well for the case of the one set of surviving conjoined twins that have “2 heads” I remember reading an article that it was only possible because they had 2 hearts and 3 lungs. I assume the same would apply to other mammals, and I imagine the energetic needs of cold blooded animals means that when these mutations occur, they’re more likely survivable.