David Day's A TOLKIEN BESTIARY is a scholarly, definitive and enchantingly beautiful explanation of all the imaginary beasts, monsters, races, nations,deities, fauna and flora of J.R.R- Tolkien's fantasy worlds of Middle-earth and the Undying Lands.
David Day has identified, analyzed and described 129 separate races. Each is lucidly explained in terms of its physical appearance, language, behavior and culture. A TOLKIEN BESTIARY does not retell their stories: its purpose is to make Tolkien’s own books more accessible by identifying his living creatures and explaining their roles in his epic world.
I guess it's just a different style.