In Deathwatch and other Warhammer 40,000 Roleplay titles, some weapons and armour have the "Primitive" quality. Armour that is not Primitive is doubled against attacks which are Primitive. Armour which is Primitive is halved against attacks which are not Primitive.
Does the "Natural Armor" possessed by beasts and some xenos (aliens) count as Primitive? It seems odd that a predator with Natural Weapons, which are considered Primitive, would suffer from doubled armour values when attacking another beast.
Particularly deadly beasts and xenos have the Improved Natural Weapons Trait, which is not considered Primitive. This is basically a requirement to harm someone wearing powered armour, like a Space Marine, but seems kind of overkill for a lion-equivalent.