http://www.scienceworldreport.com/articles/5757/20130323/comet-asteroid-killed-dinosaurs-mass-extinction-event.htm
Money quote:
The study, which was presented at the 44th Lunar and Planetary Science Conference this week, examined the 112-mile Chucxulub crater in Mexico. ...
The researchers found that, surprisingly, whatever hit the Earth generated far less debris than had been previously thought. This implied that the missile was a much smaller object and therefore, must have been travelling at phenomenal speeds in order to create the giant crater.