Spino-rottysaurus, by Kyle Mewburn
This is set in Neanderthal times and follows Arg, a human boy, and his pet dinosaur, Skeet, and they investigate a spinosaurus who is killing lots of other dinosaurs. They end up in a crazy adventure where Arg nearly gets eaten and Skeet fights the spinosaurus, who eventually gets outwitted by the Neanderthals.
These books are rather gross, which I guess is part of the appeal, but they are mostly pretty good. They would be better for 6-8 year-olds.
Reviewed by Isaac from Tawa and Homeschool , 9 years old