Ding, ding, ding!...... beat me to it. And it might not have been just simply drowning in the water either. Now this is conjecture for sure, but whatever caused "the fountains of the deep to burst forth" had to be catastrophic in scope, perhaps a MASSIVE energy release upwards from something like craters/volcanos etc. I believe I could prove there was originally a water layer in the atmosphere (which would block UV rays), and I think the event collapsed that water layer. If you study Noah's lineage, there was a feller named "Peleg", and he's the only one that had a footnote ("In his days the earth was divided"). He lived during the flood, and all those before him lived hundreds of years, while all those after him steadily decreased in lifespan. What happened??....UV could now reach the earth's surface, deterioration and death was sped up. It's plausible to say the whole realm of earth is so much different post-flood that the dinos could not live.