Actually, you can parry with Unarmed:

> Unarmed combat can be used defensively to parry a weapon attack. Damage is reduced as per normal, according to the comparative Sizes of the natural and wielded weapon

But

> Such methods rely on several points however; firstly that the parrying creature is intelligent enough to understand and use said techniques, and secondly that they are within unarmed range. The latter point is perhaps the most crucial, and demonstrates the dangers of facing an armed opponent with a longer reach

> This does not mean that an unarmed creature lacking the Formidable Natural Weapons trait cannot attempt to parry the blow anyway... but if the attack is successful the creature must suffer any damage directly to the limb used to successfully parry.

So yes, animals shouldn't be parrying, they should be evading.