Well there is really no answer for that but all I can say is that God created everything and he created them just how he wanted
The word animal means either a member of the animal kingdom, and therefore includes humans, or it means an animal as opposed to a human, in which case it doesn't. So you have to decide which meaning...
predator
i think the cricket is one
well over time the land animals change a little and they need to be underwater to live unlike their land animal ancestors