Those are good questions but this thread isn't about such details of evolutionary history. You can propose a thread if you want some answers.
The answers are, of course, available all over the web and in lots of biology books. For an interesting view of evolutionary history I highly recommend "The Ancestor's Tale" by Dawkins.
We keep threads on topic so it is easier to follow them and so posters can ignore topics they aren't interested in.
You might want to get a very basic understanding of the evolutionary model before you go into such details. From your questions it is apparent you haven't been introduced to the most simple facts about it.