Ancient creature's small commotion when captured by bloke (8)
I believe the answer is:
mastodon
'ancient creature's' is the definition.
(extinct creature)
'small commotion when captured by bloke' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'commotion' becomes 'todo' (synonyms).
'when captured by' is an insertion indicator.
'bloke' becomes 'man' (informal term for a man).
's'+'todo'='stodo'
'stodo' put within 'man' is 'MASTODON'.
(Other definitions for mastodon that I've seen before include "Large mammal" , "old jumbo" , "very old elephant" , "Old mammal" , "giant from the past" .)