Attempt to bring mammals back (4)
I believe the answer is:
stab
'attempt to' is the definition.
(I've seen this before)
'mammals back' is the wordplay.
'mammals' becomes 'bats' (bat is a kind of mammal).
'back' is a reversal indicator.
'bats' back-to-front is 'STAB'.
'bring' is the link.
(Other definitions for stab that I've seen before include "Run through - essay" , "Pierce with a knife" , "Pierce with something pointed" , "wound as Casca" , "Pierce with a dagger" .)