Extinct elephant-like mammal (8)
I believe the answer is:
mastodon
'extinct elephant-like mammal' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for mastodon that I've seen before include "Large mammal" , "Extinct elephant-like mammal" , "Extinct mammal like an elephant" , "Extinct elephant ancestor" , "Huge animal" .)