Are they what make porcupines vertebrates? (6)

I believe the answer is:

spines

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(Other definitions for spines that I've seen before include "Sets of vertebrae" , "Thorns or backbones" , "Porcupine quills" , "Snipes at backbones" , "Quills; prickles" .)

I've seen this clue in the Evening Standard.

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