Extinct creature (4)
I believe the answer is:
dodo
'extinct creature' is the definition.
'dodo' can be an answer for 'creature' (dodo is a kind of creature). I also know that 'extinct' relates to this answer.
This is all the clue.
(Other definitions for dodo that I've seen before include "Large extinct bird" , "Flightless bird, extinct since the 17th century" , "Extinct bird of Mauritius, very dead" , "Bird (whose style of very out of fashion)" , "Proverbially dead bird" .)