Of course like any other world, Aarn has animals that are not as intelligent as humans, but also do not exist, or no longer exist on our planet. This is a listing of some of the more common and notable ones.
Behemoth - Thankfully, only around a hundred of these creatures are known to exist. They are large, lumbering hulks of flesh that usually are asleep, but devour anything and everything in their path when they are awake. They resemble a cross between an elephant, cow, and a turtle. A fully grown adult practically scrapes the sky with its back, and is easily three hundred feet tall and five hundred feet long. An infant behemoth is twice the size of an elephant, and they are born in litters of three. During the maturation process, one will usually wind up killing and consuming its siblings.
Dinosaurs - Dinosaurs haven't gone extinct on Aarn, and while they are not particularly widespread, a good deal of them live on the continent of Rensvan and surrounding islands. The number of species represented however is limited, and has not yet been decided yet - only dinosaurs that have evidence of living in jungle or savanna will be included, and many of the more prehistoric species will be overlooked. Also, a good deal of dinosaurs with evidence for it (such as velociraptors and t-rexs) will very likely be given feathers.
Other Prehistoric Creatures - More megafauna that has gone extinct more recently in the history of Earth such as mammoths and saber-toothed tigers are indigenous to the frozen mountains and plains of Habruk, though the tigers tend to stick to the areas with a milder climate, not being built for extreme cold.
Kraken - A massive squid that often claims human oceangoing vessels. Kraken have no known intelligence and their tentacles are powerful enough to rend even the mightiest of ships in twain. They have never been accurately measured, but estimates range from 300 to a full thousand yards from the tip of the tentacle to the end of the head.
Leviathan - While not technically a natural animal, the Leviathan bares mention here. It is largely this creature which makes the Great Barrier Sea a barrier - it actively hunts and consumes all oceangoing vessels attempting to sale between the southern coast of Zenninfal to the Jerohm Peninsula. Estimated to be a massive eel a mile in length, this creature is actually an organically grown battleship controlled by the merfolk race. The merfolk have many other similar "creature ships" they use for transportation and military action, but none so large or effective.
Rocs - Often confused with phoenixes, rocs are giant eagles with 40 foot wingspans. They range in color from brown, to white, to gold. They roost in tall mountain ranges and will often prey on large herbivores like horses, elephants and giraffes.
Sea Mosquitoes - Sea mosquitoes are gigantic insects with proboscises that are 4 feet long. They feed on the blood of World Turtles and often travel in massive swarms. A ship sailing into a swarm of sea mosquitos is in a great deal of trouble - they have the strength to shred wood, and being stabbed with their proboscis is not pleasant. Because their proboscis is so long, it is difficult for them to easily drink the blood of sailors. However, they still can if they manage to find the heart and hold their victim steady.
World Turtle - An aquatic version of the behemoth, a world turtle will sleep on the surface for hundreds of years, and often are mistaken for islands. They share a shell with behemoths, though the dirt and vegetation that accumulates on their backs tends to hide this feature. Sizes range from a few hundred feet to a few thousand. It is wise to never awaken a world turtle, because its appetite is as insatiable as its land-dwelling cousins.
Wyrvn - A mundane animal that is very similar to a dragon, a wyrvn has no magic and very little discernible intelligence. Their arms double as their wings, like a bat, and they only have two legs. Their tail is also notable for having poisonous barbs at the tip. Their wingspan is 60 feet and they can often be confused for dragons, though they are decidedly less dangerous.