US notary ran broadcast on an extinct creature (11)

I believe the answer is:

tyrannosaur

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

'an extinct creature' is the definition.
'tyrannosaur' can be an answer for 'creature' (thesaurus). I am not sure about the 'an extinct' bit.

'us notary ran broadcast' is the wordplay.
'broadcast' is an anagram indicator (letters scattered or cast around).
'us'+'notary'+'ran'='usnotaryran'
'usnotaryran' anagrammed gives 'TYRANNOSAUR'.

'on' acts as a link.

Can you help me to learn more?

(Other definitions for tyrannosaur that I've seen before include "Large extinct reptile" , "Monstrous beast" , "Large Cretaceous carnivore" .)

I've seen this clue in the Sydney Morning Herald.

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