This is a pretty interesting question. First, as a creationist that holds to the idea that the flood and its attending consequences is largely responsible for the fossils we find, I would suggest that almost ALL (more than 99% would be my guess) of the dinosaur fossils that have been discovered were alive at the time of the flood. So if that idea is correct, it means that the feeding of such creatures might represent a serious burden to the earth, as you suggest.
Well, there are several factors that could play into the equation.
- How many dinosaurs there were.
- How much land area was available for them, and
- How well did the land support the dinosaurs.
On #1. I couldn't find an answer--maybe [MENTION=15431]6days[/MENTION] knows. I saw one estimate of about 2100 "good" fossil dinosaur skeletons worldwide, "good" meaning maybe about 60% of the bones. But let's just say for a minute that because of the unusually good conditions for forming fossils that occurred during the flood, compared to the unusually poor conditions that occur when animals die today, that maybe 0.1% of the dinosaurs were actually fossilized, and let's say the total number of fossils that belong to different animals is over 1000 times the number of good fossils out there. That puts the potential number of actual dinosaurs at the time of the flood at 2.1 billion dinosaurs (I think that may be conservatively large??). And I've heard that the average size of a dinosaur was probably about the size of a sheep.
So, in the world today, there are approximately 1 billion
domestic sheep, the same number of pigs, and maybe 1.4 billion cows (
see here). I think that would put the amount of food needed by dinosaurs somewhere less than the current needs of just the 3 most popular domesticated food animals today. And they are doing pretty good along with over 6 billion people (also about the same size as sheep), and a whole bunch of cats and dogs, not to mention
all non-domestic animals. The number of the very large dinosaurs is probably pretty insignificant compared to the total land area.
On #2. It's hard to know what the world looked like before the flood. It likely had a lot more land area, but if the current amount of water in the world doesn't cover the mountains, then it's also likely that the mountains were smaller, so more land was available to the lowland-type creatures (as dinosaurs seem to have been, preferring swamps or similar landscapes).
Plus, if much of the water that fed the flood was from underground, then it's likely the seas were smaller.
On #3. If more lowland, and fewer mountains, and a climate that could sustain dinosaurs even in Antarctica, the land would be able to sustain the animals quite well, it seems.
Of course the dogs, cats, cows, sheep, pigs, etc. were also there, but we've also had more than twice the amount of time since the flood for the numbers to grow, compared to the time from creation to the flood. It doesn't really seem like that big a deal to me.