Mistake, catching extremely insular creature (7)
I believe the answer is:
giraffe
'creature' is the definition.
(I've seen this before)
'mistake catching extremely insular' is the wordplay.
'mistake' becomes 'gaffe' (gaffe is a kind of mistake).
'catching' means one lot of letters goes inside another.
'extremely' suggests removing the centre (only the extremes of the word are used).
'insular' with its centre taken out is 'ir'.
'gaffe' going around 'ir' is 'GIRAFFE'.
(Other definitions for giraffe that I've seen before include "The tallest animal with long neck" , "Lofty browser's" , "Long-necked browser" , "Fire fag at the animal" , "Tallest mammal" .)