This is like an encyclopedia of dragons and related creatures, treated totally seriously and giving not only size and colour information, but native area, natural habitat, diet and everything you would expect of any encyclopedia of animals.
It goes much further than just differentiating between a Dragon and a Wyvern, but explains creatures less familiar like Amphipteres and Jormundganders, Sea Orcs and Hydras.
I'm not sure of the authority for some of the 'facts', but I suspect a combination of established mythology and gaming manuals.
Explaining the relationships with some recognisable mythological creatures like the Cockatrice adds interest.
The artwork is fantastic. The pre-release Kindle copy doesn't display it to best effect, but I downloaded the PDF version to see it in full color. This is a book worth getting in hard copy for the art alone!
An excellent resource for any Fantasy fan's library.