There is a daily achievement called Daily Kill Variety. I'm curious if there is a list anywhere of what the different enemy types are and what enemies belong to each type. Today I killed a Ram, a Moose, and a Doe and I only gained 1 toward this achievement (starting from 0 for the day). Clearly these are all the same type.
The bestiary category on the official wiki is a good guideline, each of the subcategories generally count as their own creature type for kill variety.