Dragon Book or Book of Dragons is a collection list. Each Dragon (Baby-Juvenile-Adult) will counted by 3 if your dragons are in level 7 to 30. When you have 5 Dragons (15 Photos of Baby - Juvenile - Adult) you will receive Gems. When you completed a whole collection with Rare Dragons will receive more gems than the Elementals and Hybrid.
In total, so far, there are 246 different evolutions, 3 for each dragon. The 3 different evolutions are the baby, adolescent and adult. Your total progress is kept track of in the top left corner when you open The Book of Dragons, which is accessed through pressing the "Storage, news and much more" -button (the globe situated to the upper right of the "Build" button).
In addition to this, a collection of either 4 or 5 dragons can be acquired to claim rewards consisting of between 2 - 5 gems, i.e. "The Frosty Collection", consisting of all the 3 stages of Ice Dragon, Blizzard Dragon, Icecube Dragon, Alpine Dragon and Cool Fire Dragon will reward you 2 gems.
- The dragon book shows you 201 dragons, but only 67 released (with specials, 130). For every level of dragon (baby, adolescent and adult)it shows 1 dragon.