Evan\'s Dinosaur Question

We were driving to a birthday party.  Olivia and Evan were sitting in the back seat talking about Dinosaurs which is a popular topic between them. 

Evan asked me WHEN the dinosaurs died.  I said something vague like a 'long long time ago'.  Then he asked HOW they died.  I mentioned that some people think a giant asteroid hit the earth and a lot of dust went into the air which blocked the sun and the dinosaurs couldn't live like that.

Sounded good I thought.

But right after I was done, Evan asked:  "But what about the sea dinosaurs?  They don't need a clean sky."

Good point Evan!  I never thought about that.  I don't know why the sea dinosaurs would necessarily become extinctJ.