I believe the word you're looking for is zoomorphism

One of the problems in these searches for lesser used words (be honest, when was the last time you used zoomorphism in everyday conversation?) is that various dictionaries give different definitions for the word. For example for "zoomorphism" one finds variations of:
- conception of a god or man in animal form
- Attribution of animal characteristics or qualities to a god
- The transformation of men into beasts

The only online definition of "teriomorphism" I can find online gives:
- the belief that gods exist in animal form


So as an antonym to "anthropomorphism", my vote goes to "zoomorphism" since at least one definition uses both men and gods, and at least one (other) definition allows both form and other characteristics.

Rod