Herbivorous dinosaur (9)
I believe the answer is:
stegosaur
'herbivorous dinosaur' is the definition.
(herbivorous dinosaur from Jurassic period)
This is all the clue.
(Other definitions for stegosaur that I've seen before include "Armoured fossil creature" , "Old beast" , "old dinosaur" , "Old veggie" , "Jurassic creature" .)