Joining a team later as a co-founder
agotterer: I was in a similar situation. I was "recruited" as a co-founder and CTO about a month after the idea was born and organized,  but nothing built. I was given a smaller percent then the other founders, but adequate for what I brought to the table. As another commenter mentioned, an even split doesn't always happen even when everyone is there from day one. At this early stage its all about who brings what to the company...