For quite some time, my 4yr old's favorite dinosaur book was My Big Dinosaur Book. Recently, however, he asked me to find him "a serious dinosaur book." So, I searched our public library, and found First Dinosaur Encyclopedia. My son loves this book.
It begins by disucssing how different the Earth was when dinosaurs existed. Illustrations show the changes between the Triassic, Jurassic, and Cretaceous periods. Not only are dinosaurs from each period featured, but details about plant life and fossilization are included.
Both the drawings and photographs remind me of the Discovery Channel shows like When Dinosaurs Roamed America. The actual information is extremely well-organized, making it very easy for any young student to write a report or essay using this book, on his or her own. Pages also, include "buttons" that have either a reference to another selection in the book, or some unusual fact is highlighted. In addition, the glossary contains words that would make a great vocabulary list.
I recommend this dinosaur encyclopedia to anyone interested in the subject; keep in mind this is intended as an introductory encyclopedia.