Oops – silly amounts of marsupials (8)

I believe the answer is:

opossums

'marsupials' is the definition.
(opossum is a kind of marsupial)

'oops silly amounts' is the wordplay.
'silly' is an anagram indicator.
'amounts' becomes 'sums' ('sum' can be a synonym of 'amount').
'oops' anagrammed gives 'opos'.
'opos'+'sums'='OPOSSUMS'

'of' is the link.

(Other definitions for opossums that I've seen before include "Small, furry, Australian marsupials" , "American marsupials" , "Mainly arboreal marsupials" , "American natives" , "animals" .)

I've seen this clue in The Everyman puzzle in The Observer.

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