An object that killed the dinosaurs roughly 66 million years ago may have been a comet, rather than an asteroid, say researchers Prof Jason Moore and Prof Mukul Sharma at Dartmouth College, New Hampshire. An image shows a comet striking coastal Yucatan, forming the giant Chicxulub impact crater and causing the extinction of the non-avian dinosaurs (Don Davis / NASA) Something killed off almost all the dinosaurs and some 70 percent of all other species...