Disappointing. Hard to imagine how a book about time-travelling back to see the dinosaurs could be boring, but here you are.
I made it to page 200, when I decided I could take no more. I wonder if Swanwick's enthusiasm for his topic (and there clearly IS enthusiasm, and solid research, and underlying ideas -- that's the source of the extra star) overwhelmed his narrative sense. Dinosaurs are interesting (natch), going back to see dinosaurs, and research them face to face, is interesting, therefore anything you write about dinosaurs and time travel must be interesting. Sadly, not true.
Gets off to a reasonably good start, with Mystery Man Griffin visiting paleontologist Richard Leyster with An Offer He Won't Want to Refuse -- and a cooler with the freshly decapitated head of a stegosaurus. Great! It then, immediately, goes seriously off the rails, as the next 100 pages or so are basically a long, very long series of infodumps and character introductions (too many, too minor characters to keep track of and wonder if there's any reason to care about). Characters criss-cross time threads, actually meet and advise their younger/older selves: in this version of time travel, we are told, neither the butterfly effect, nor the grandfather paradox, nor the potential danger of encountering your past or future self is a problem, giving Swanwick free rein for all sorts of "fun," such as when a 13-year old girl with a crush on Leyster leaves by one door, and promptly re-enters by another, as a foxy 20-something who is determined to do something about that crush. Oh, what larks ...
It's all a bit boring and confusing, really, with only hints and whispers about Griffin's darker side, and the ulterior motives of the advanced beings who have gifted humanity with the time travel tech. Caring about any of the characters would have helped a lot, but there are too many of them, too randomly introduced.
By about page 150 we (finally!!) get to the part when some paleontologists are in danger of getting chomped by a T. Rex! But by then, for me, it was too little actual story, too late. I need an older, wiser version of Me to come back when I was at about page 10, and tell me that this was not going to end well ...
INteresting plot where paleontolists got into the past to study dinosaurs. Interesting plot twists and fun to read.
A bit of a yawn. James Rollins does a much better job with this kind of subject matter.