So, as I vaguely remember it. It was set in the distant future were a dictator rules the Earth. By this point carbon dioxide was so high most life outside of humans was extinct. So the dictator built a special zoo with the right atmospheric conditions. Then he sent crews back in time to retrieve things. But, unbeknownst to them they were sliding sideways through the dimensions. So when they went to get a horse they got a unicorn instead, a real drake instead of a komodo dragon, etc. The unicorn gored one of them really bad. The drake burned another pretty bad.
Somewhere along the way they speculate on what happened to the rocs of myth and figured it was the ostrich and they re-enabled the disabled DNA pairs and suddenly had a roc that broke free, escaped, and quickly suffocated to death in the high CO2 atmosphere.
I remember them all nearly dying because someone sent to get the first automobile built by Henry Ford screwed up and accidentally destroyed the original. And that changed time so that Ford never started an auto industry so the air never got polluted, etc., and everyone in the future, accustomed to the high CO2, was dying without it.
Does anyone know the author and book/story names?