Source of extinction level asteroid

Here's an interesting hypothesis on the origin of the asteroid that scientists think struck the Yucatan and killed the dinosaurs at the KT extinction 65 million years ago. A massive collision in the asteroid belt that exists between Mars and Jupiter is identified as the source in the study. The study is interesting as they've taken orbits of existing groups of a family of shattered asteroids and worked backwards to the point in time when a collision broke them apart from what used to be a much larger asteroid.