The most common and most likely answer to this crossword clue is the 11 letter word TRICERATOPS
I've seen this crossword clue in The Times
T
R
I
C
E
R
A
T
O
P
S
More clues leading to the result TRICERATOPS
- Dinosaur artist coming in second best
- Treat a critter with surgical procedures, old herbivore
- Instant trap so designed for dinosaur
- After very short time, pastor abandoned defunct browser
- Second artist covers dinosaur
- Fossil I spot with crater being disturbed
- Moment pastor reconfigured defunct browser?
- When travelling, spot erratic old creature
- Dinosaur hoax, not last, best in ages
- During journeys, muse on Conservative dinosaur
Buddy explains!

The straight part
We know that "creature no longer living" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case creature no longer living = triceratops.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TRICERATOPS mean?
TRICERATOPS noun- Common name of the extinct genus Triceratops; a herbivorous ceratopsid from the late Cretaceous.