Animal succeeded? Exactly (5)
I believe the answer is:
stoat
'animal' is the definition.
(type of rodent)
'succeeded? exactly' is the wordplay.
'succeeded?' becomes 's' (genealogical abbreviation).
'exactly' becomes 'to a t' ('to a T' can mean exactly right).
's'+'toat'='STOAT'
(Other definitions for stoat that I've seen before include "European ermine" , "Weasel-like mammal" , "Short-tail weasel" , "Small carnivore" , "Member of the weasel family" .)