Extinct elephant-like mammal (8)
I believe the answer is:
mastodon
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">extinct elephant-like mammal</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(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" .)