Marsupial in group with one bird (9)
I believe the answer is:
bandicoot
'marsupial' is the definition.
(bandicoot is a kind of marsupial)
'group with one bird' is the wordplay.
'group' becomes 'band' (band is a kind of group).
'with' says to put letters next to each other.
'one' becomes 'i' (Roman numeral).
'bird' becomes 'coot' (coot is a kind of bird**).
'band'+'i'+'coot'='BANDICOOT'
'in' is the link.
(Other definitions for bandicoot that I've seen before include "Australian marsupial with long pointed muzzle and tail" , "Little animal" , "native of Australia" , "Insect-eating marsupial of Australia and New Guinea" , "Aussie native" .)