From the introduction:
The burnt world of Athas is comprised of a variety of dangerous and treacherous lands, from sand swept deserts to rocky badlands, bleak salt flats to plant choked jungles, and craggy mountains to the volatile Sea of Silt.
One things that all these places have in common is that danger lurks in every direction, both from the inhospitable terrain but also the deadly creatures that roam them.
This book details many of the creatures that might be encountered under the Dark Sun, includings those from the more civilized races and domesticated animals, vicious creatures of the wild, dangerous man-eating plants, and deadly gargantuan beasts.
This collection is by no means a complete record of all the creatures of Athas, as surely there are many monsters that have devoured any who have been unlucky enough to encounter them.