I've read some interpretations that claim that dinosaurs, and other prehistoric life may have been around in this first sentence in Genesis. "In the beginning God created the heavens and the earth. Day one starts after this creation. I guess the thought is that since dinos aren't relative to the purpose of the Bible, why mention them. Anyhow, I suppose that God would have chosen to start over with what we know of as creation following that. I can't say that this is my belief, but I suppose it's a possibility.
"Well, isn't that con-veeen-yent!"
I suppose there are all sorts of possibilities. But I have to rely on what the Bible actually says.