nowadays our technology is far advanced then our imagination. there are some evdiences from which scientists pridicts that cause of extinsion of dinosaurs. Fossils, Imprints and other things shows the ancient climetic condition condition. using carbon dating process scientists determines age and environmental and climetic condition of that period.. they use these things as basis of their reserch and print their thesis.. so till now no sure evidence has been found...theory of Darvin, lamark tells us same things that dinsaurs extinct beacause of "shortage of food, struggle for existance,, etc"
hope this helps u.......i u have any confusion then u can ask.