A while back my Google box was running an ad for Cretaceous Dawn, a book I had to look into just because it would have made a great alternate title for Dawn of Time. The book is about some people who accidentally invent a time machine and find themselves whisked back to the time of Dinosaurs, and that's pretty much all you need to know, but there's a couple interesting time travel-related twists, as well as an ongoing investigation in the present day where people are trying to figure out where our protagonists went. It's not without its corny moments (its got pretentious "quotes" from the characters at the start of each chapter) and I thought the ending was a bit of a letdown (I was left feeling like there were some plot holes), and the made-up name "Yariko Miyakara" irritated me every time I saw it, I am certain if anyone who spoke Japanese had been asked they would have changed it to something more authentic (Yuriko Miyakawa would have been fine!). On the whole I was pretty drawn in and would certainly recommend it if the concept appeals to you.