From the feature list:

Creatures

Xsyon is populated with player humans and non player undead, animals and mutants. Creatures can be hunted or become the hunter.

No set creature spawns or re-spawns. Animals multiply based on the current creature population. Undead never truly die, or do they?
Creatures gain experience and power, potentially evolving into legendary beings.
Creatures can overrun areas or be depleted.
Creatures gravitate towards different areas based on mood and weather.
Creatures driven to the outer reaches of the world mutate.
Creatures possess realistic loot. If you see armor or a weapon on a creature you can take it. Animals can be carved up for raw materials.
Creatures are a primary resource for crafters.
You can see images of them in some of the old screenshots in the gallery too.