Hm, what about an aberration tag? For cases like post #153313 and most of meandraco's stuff

post #669564

Either as a replacement for monster, or a more specific subcategory for the more 'alien' types
(see my response about aliens below as well)

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It's an official term as well:

Zoological definition [wiktionary]:

(zoology, botany) Atypical development or structure; deviation from the normal type; an aberrant organ. [Mid 19th century.][3]

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However, since the definition is so broad, it may end up being synonymous with alien anyway, so idk:

• alien: non-human, extraterrestrial
• aberration: any species that doesn't fit into the common, non-modifier body style types (anthro, feral, human, humanoid etc.)

Oh yeah, about the chakat/taur thing; changed

Taurs are [somethin] + feral though, which raises an interesting question:

Are hybrid types considered mutually exclusive for categorization purposes?

feral + * = taur is the only example that I can currently think of

It's somewhat obvious now that animal_humanoids are of the humanoid type too. Removed.
I have the feeling there may be more to it though, but it's consistent for present tagging purposes afaik anyway

As for aliens..hmm

You may be right about there being no standard definition, by the very nature of the term.
And more significantly with respect to mutually-exclusive types, since it's more or less a type modifier (anthro, humanoid, 'feral' aliens exist in media), it probably doesn't count here

Maybe the abovementioned aberration or similar for cases that don't fit into any of the pre established ones?

monster, aside from the pejorative implications, is also a type of modifier, like you said.
There are anthro monsters, feral ones, humanoid ones etc.

Do we consider the modifier types like flora_fauna, alien, goo etc. for mutually-exclusive body styles?

I'm guessing 'no'