Ancient beast not so mad perhaps (8)

I believe the answer is:

mastodon

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

'ancient beast' is the definition.
'mastodon' can be an answer for 'beast' (mastodon is a kind of beast). I am not certain of the 'ancient' bit.

'not so mad perhaps' is the wordplay.
'perhaps' is an anagram indicator.
'not'+'so'+'mad'='notsomad'
'notsomad' anagrammed gives 'MASTODON'.

Can you help me to learn more?

(Other definitions for mastodon that I've seen before include "Extinct elephant-like mammal" , "giant from the past" , "Large extinct animal resembling elephant" , "Old mammal" , "Big beast" .)

I've seen this clue in The Sun.

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