Darwin and fossils

So, we just celebrated Darwin Day, which was really cool.  But, I have a question to present to everyone.  This could be a cool little thought experiment.  If we could spend a little time with Darwin (He rises from the grave to see the progress we have made with his big idea) and we only had time to show him ONE fossil, which fossil would you choose to show him and why?  

Obviously the fossil record has lead to a great understanding of evolution and has supported much of what Darwin proposed.  I think it is fun to think about where his ideas may have gone if he had the fossil record we have today to ponder.  

Think and talk amongst yourselves.  Pura vida.

mason