Dolt! There were no living plants left, so the herbivorous dinosaurs died rather soon (yes, they went extinct), and the carnivorous beasts (lions, etc.) fed off their carcasses. The horses, cows and such continued to live off of what was stored on the ark. That kept them alive until plants returned, and then all went back to normal. Why can't you satanic science guys understand?
</creationism mode>
Q. What's harder than getting a pregnant brontosaurus in the ark?
A. Getting a brontosaurus pregnant in the ark!
So was that a simulated olive branch with leaves that the dove returned with in her mouth? Maybe one of those nice plastic ones you can by at the Arts and Crafts store?