I'm sorry if this question has been asked before but what are the main differences, if any, between Mark Sissons, Loren Cordain and Robb Wolf's paleo/primal ideas? Am I correct in thinking these are the three main paleo writers?

I've only been paleo for about 6 weeks having found Mark's blog and then read two of Cordain's books and various other bits and pieces. Has anyone read all from all three authors?