In our sad arrangement, one unable to adapt? (8)

I believe the answer is:

dinosaur

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'one unable to adapt?' is the definition.
I can't tell whether this definition defines the answer.

'in our sad arrangement' is the wordplay.
'arrangement' indicates an anagram.
'in'+'our'+'sad'='inoursad'
'inoursad' anagrammed gives 'DINOSAUR'.

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(Other definitions for dinosaur that I've seen before include "Old-fashioned type" , "Creature no longer" , "Extinct terrestrial reptile" , "I adorn US with this old creature" , "Extinct reptilian animals" .)

I've seen this clue in The Times.

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