Crossword Genius

Fools adopting a billion animals (9)

Ross

I believe the answer is:

wallabies

'animals' is the definition.
The answer is an example.

'fools adopting a billion' is the wordplay.
'fools' becomes 'wallies' (wally can mean a stupid person).
'adopting' means one lot of letters goes inside another (inserted letters are taken on or adopted).
'billion' becomes 'b'.
'a'+'b'='ab'
'wallies' placed around 'ab' is 'WALLABIES'.

(Other definitions for wallabies that I've seen before include "Marsupials" , "Pouched jumpers" , "bounders" .)

I've seen this clue in The Times.
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