There are other questions like the enormous size of the pre-flood plant life.
One theory is that the atmospheric pressure was as much as three times higher due to a protective layer which held a layer of frozen water in the upper atmosphere.
That environment would be like a hyperbaric chamber, which would increase both O2 and CO2.
After the flood, the atmospheric pressure is reduced, growth of both plant and animal life is stunted.
Even if there were dinos on the ark, all the large species would have a tough time surviving.
Well it does make for a long-lived story.