Long-necked mammal (7)
I believe the answer is:
giraffe
'long-necked mammal' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for giraffe that I've seen before include "that's beastly" , "Tallest beast" , "Tallest extant quadruped" , "Large African mammal" , "Long-necked browser" .)