In Ark: Survival Evolved, creatures can have various hitboxes that modify damage when hit. 34 creatures have head hitboxes, meaning a headshot will deal significantly more damage and torpor (for most creatures, 3 times more).
Only 43% of creatures (34 of 79) have headshot modifiers. Note that this list only includes tamable creatures (with the exception of the Titanoboa.)
All flying creatures have 3× headshots, besides the Onyc.
Swimming creatures do not have headshots or any other modifiers.
The Pachy is the only creature that has a negative headshot modifier (shooting its head deals less damage/torpor).