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Fossils — a couple of thousand on new site (9)

Ross

I believe the answer is:

ammonites

'fossils' is the definition.
(ammonite is a kind of fossil)

'a couple of thousand on new site' is the wordplay.
'couple of' says to double the letters.
'thousand' becomes 'm' (Roman numeral for a thousand).
'new' indicates anagramming the letters.
'm' duplicated is 'mm'.
'site' anagrammed gives 'ites'.
'a'+'mm'+'on'+'ites'='AMMONITES'

I've seen this clue in The Guardian.
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