ZE ICE AGE!!!!
God. Man knew magic which created dinosaurs thus the fall of Babylon and the mighty destruction of sorcery so that man will never yield such magic ever again. This killed the dinosaurs.
Your mom came hurtling through space and struck the earth; the hamplanet impact's resulting with the aforementioned chain reaction of catastrophic ecological phenomena was enough to send the 'saurs into a downward spiral of survivability.
Your fucking mom.