Sounds like a fossil Pokemon.
'Gentle Herbivore' makes me think Aurorus, but that doesn't fit with the 'head harder than steel' part afaik.
'
head harder than steel', for a fossil Pokemon, makes me think Rampardos. Idk if it's a herbivore but judging from it's Dex Entries it's definitely not
'Gentle'.
Pearl - Its skull is as hard as iron. It is a brute that tears down jungle trees while catching prey.
Ultra Sun - In ancient times, people would dig up fossils of this Pokémon and use its skull, which is harder than steel, to make helmets.
Guess I'll just keep going with fossil Pokemon:
-Tyrantrum -> Neither gentle nor a herbivore. It preyed on Amaura.
-Bastiodon -> Did not know this was a herbivore tbh. Fits gentle Herbivore and has a head made of steel. Best fit so far.
-Kabutops -> Not a herbivore. Hunts prey and drinks their body fluids.
-Omastar -> Not a herbivore. Preyed on Shellder amongst others.
-Aerodactyl -> Dunno whether or not to take 'walked the Earth' literally but aside from that it's PokeDex entries describe it as Ferocious/Savage/Vicious etc.
-Cradily -> Lives in the water and hunts for prey.
-Armaldo -> also hunts for prey.
-Carracosta -> Preys on Omanyte and Omastar and devours them whole. Not exactly a gentle Herbivore either xD
-Archeops -> Is omnivorous.
Gonna ignore the gen 8 fossils as they are a scientist's mad creation rather than mons that actually exited long ago.
I'll go with Bastiodon.
"Holds its own strength in high regard and often acts selfishly. When it meets a person or another Pokémon, it won't initiate an attack, but it will taunt them until they start a fight."
