Crossword Genius

Are they unique in bone structure? (4)

Ross

I believe the answer is:

ones

I'm a little stuck... Click here to teach me more about this clue!

'are they unique' is the definition.
The definition suggests an adverb but the answer is not.

'in bone structure?' is the wordplay.
'in' indicates a hidden word.
'ONES' is hidden in the letters of 'bone structure'.

Can you help me to learn more?

(Other definitions for ones that I've seen before include "Units" , "1 & 1 & 1" , "Individuals" , "Singles" , "Aces" .)

I've seen this clue in the Evening Standard.
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