You do not know if all of those things are from the Earth at all or if they had been changed by some sort of engineering. OK, we find fossils of horse-like animals in grassland environments. But I should be open to the notion that they're not of the Earth at all. IMO, this is simply silly.
I'll stick with Occam until someone produces evidence of some sort of ET activity or of "engineering".
Neither one is observed in the modern world (until maybe 20 years ago), there are no fossil gene splicers or test tubes or whatever, and as I said, some of the fossil species merge imperceptibly into each other.
In fact, the modern species aren't all that well separated.
You can't prove that something doesn't exist.
Do you creationists actually believe that Noah build a boat big enough to put two of every animal on it. Even animals that lived on different continents? I still can't believe people 2000 years ago were stupid enough to believe that is possible. Plus wouldn't that mean all humans are descendants of Noah. How do you explain black, Chinese, native American people having totally different features?