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

I’m going to take a crack at this.

So species like sharks, lions, and such give live birth. And two headed ness is a birth defect, there are also chances that there are more defects in the offspring while its forming in uterio, causing a strain of the female’s body as it tries to carry the offspring to term.The female’s body carrying the offspring would abort the pregnancy (miscarriage) due to this strain on its resources (nutrition, water, and just strain of a difficult pregnancy). Also, I would think the offspring would die during the birth process, perhaps getting stuck in the canal, perhaps taking the female with it, and then them being eaten by scavengers would also reduce the likelihood that we would even see bones of remains.

Turtles, snakes and such are born mostly in eggs (some snakes do live births), with all the genetic martial and nourishment the offspring needs, not relying on the female’s body to “monitor” ( for lack of better word) how that offspring is doing. They are able to break open their egg, but don’t usually live long afterwards without intervention.