Most of the dinosaurs died in the global flood of Noah's day (Genesis 7:20-21).

Some dinosaurs probably died due to post-flood climatic changes. Before the flood, the earth had a warm climate across its entire surface. A water vapor canopy (Genesis 1:6-7) would have produced a global greenhouse effect. Following the flood, after the condensing of the canopy which fell as rain, the earth experienced severe seasonal changes for the first time (Genesis 7:20-21).
The dinosaurs had neither fur, blubber, nor feathers for insulation against the cold, nor were they able to hibernate as reptiles and amphibians. Most of the dinosaurs that got off the ark (see picture below) at Mount Ararat (Genesis 6:19; 8:4,19) were unable to migrate to warmer latitudes before the first cold winter arrived and perished in the frigid weather. A few of the dinosaurs, such as the behemoth, were able to migrate far enough south to survive the winter (Job 40:15-24).

Some dinosaurs may have been hunted to extinction by men like Nimrod (Genesis 10:9). Both ancient Babylonian writings and Jewish tradition state that Nimrod became a famous hunter of great beasts.

Some dinosaurs lived as late as Job's time (Job 40:15-24; 41:1-34), and some of the dinosaur-like sea dragons lasted even longer (Psalm 104:26).