Following their road win over the Raiders, the Lions played their Week 2 home opener against their NFC North rival Minnesota Vikings for the lead in the division.  After a scoreless first quarter, Detroit pounced first with QB Jon Kitna completing a 9-yard TD pass to WR Roy Williams.  The Vikings tied the game with QB Tarvaris Jackson getting a 1-yard TD run.  The Lions took the lead prior to halftime with kicker Jason Hanson's 30-yard field goal. In the third quarter, when Kitna was temporarily out with a concussion, QB J. T. O'Sullivan came in and completed a 7-yard TD pass to Calvin Johnson to increase Detroit's lead.  Minnesota, however, tied the game up with kicker Ryan Longwell getting a 32-yard field goal and DE Ray Edwards returning a fumble 9 yards for a touchdown.  After both teams failed to score in the fourth quarter, the Vikings got the ball to begin overtime.  The Lions forced a fumble nine plays into their drive and would eventually get the win with Hanson's 37-yard field goal.
Question: Who replaced Jon Kitna at quarterback?
Answer: J. T. O'Sullivan