The impactor believed to have wiped out the dinosaurs and other life forms on Earth some 65 million years ago has been traced back to a breakup event in the main asteroid belt. A joint U.S.-Czech team from Southwest Research Institute (SwRI) and Charles University in Prague suggests that the parent object of asteroid 298 Baptistina disrupted when it was hit by another large asteroid, creating numerous large fragments that would later create the Chicxulub crater on the Yucatan Peninsula as well as the prominent Tycho crater found on the Moon.
Southwest Research Institute News

Abstract: An asteroid breakup 160 Myr ago as the probable source of the K/T impactor

Baptistina asteroid family
(PDF from the 2007 meeting of the Lunar and Planetary Institute)