A monster family tree

Scientists often try to arrange animals into a kind of family tree:

To try to do this we've been creating some little monsters, starting with this one:

Someone changed this one a bit. The next person changed one of those first two, and so on.

The challenge then was to work out how all the monsters we'd made had evolved, how they were all related:

No two of our "family trees" was exactly the same, so there's perhaps more thinking to do...