West of Eden is a 1984 science fiction novel by American writer Harry Harrison. I've read it. It's actually a small series. I like the story.
In the parallel universe of this novel, Earth was not struck by an asteroid 65 million years before the present. Consequently, the Cretaceous–Tertiary extinction event which wiped out the dinosaurs and other reptiles never happened, leaving the way clear for an intelligent species to eventually evolve from the mosasaur, a species of reptile related to the modern monitor lizards. This relationship would mean that the intelligent species are not dinosaurs but lizard-people.
The lizard-people are known as the Yilané, and are the dominant life form on most of the planet. However, during the evolutionary process, the species became non-viable on the two American continents, leaving them free of Yilané for millions of years and opening an ecological niche for a top predator. A human-like species, the Tanu, evolved to fill the niche in North America, but are only found on that continent. By the time the novel begins, the humanoids have reached a late stone age level of technology and culture, with a number of societies having developed farming skills.
http://en.wikipedia.org/wiki/West_of_Eden
It is an interesting What-if scenario to explore.
There are lot of alternate earth or dinosaur and human science fiction stories out there.
I really like the ideas of Jurassic Park as optional genetic engineering alternate timeline play.
Heck we're trying to bring back a mammoth right now.
http://www.telegraph.co.uk/science/science-news/8257223/Mammoth-could-be-reborn-in-four-years.html
Yeah, the dinosaurs existing with humans is creationist-crazy inspired religious ignorant nonsense. But could be a lot of fun to play with
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Also a random event that creates them in the modern or transhuman eras.. like Jurassic Park
