The extinction of the dinosaurs removed a major food competitor, and predator, of smaller animals. As a result of a new "vacancy" in the food chain, following the [[K-T Event]], vast speciation occurred, as the evolutionary pressure of a new cold age propelled animal species to adapt or die out. What we now know as [[mammals]] were some of the main beneficiaries of this explosion: their fur allowed them to adapt to the cold, and their small size allowed them to conserve energy relative to the huge dinosaurs of the previous age.<ref>Bennet, Shostak, Jakotsky, "Life in the Universe," viewable at http://www.amazon.com/Life-Universe-Jeffrey-Bennett/dp/0805385770</ref>