Aggressive branch of the animal kingdom (6)

I believe the answer is:

antler

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'aggressive branch' is the definition.
'antler' can be an answer for 'branch' (I've seen this before). I am unsure of the 'aggressive' bit.

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for antler that I've seen before include "part of Rudolph" , "One on stag's head" , "Stag horn" , "One seen on stag" , "Branched animal horn" .)

I've seen this clue in The Globe and Mail.

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