A better question would have been, "What would ANY of the animals have eaten?" Plants don't just spring up overnight either, so the herbivores would have been screwed, too, coming off that boat to a soggy, brine-soaked wasteland that had been the floor of a worldwide ocean for a year.
(Even when hearing this stupid myth as a child, I always thought that the dove bringing back a leafing olive branch was silly, since I knew it would take much longer than that for trees to make any kind of comeback from a disaster like that. I was a child, and this was obvious. I can't imagine the brainlock required for adults to not get it.)
But, yes, carnivores eat only other animals, and the only animals available to eat, according to the story, were the ones on the ark. You can't just arbitrarily declare that they didn't eat meat yet until there was a stable population of prey animals just because that's the condition you need to plug that particular hole in this sieve (rather than on the basis of any evidence whatsoever, and in fact in direct contradiction to the mountainous total of evidence available).
The tale of the flood, as it stands in Genesis, is already ludicrous. But the more these folks try to rationalize it and reconcile it with reality, the sillier it gets.
~David D.G.
