Also, you are permitted to take command of a guild master from the legal guilds. Here are the current masters of the legal guilds and who they are.

Twin Tails = Marcorav (Jeholornis) - Taken By Me

Sabertooth = Wulf (Ivantosaurus)

Earth-Shaker = Winston (Apatosaurus)

Sloth's Talon = Malcom (Giant Ground Sloth)

Pirate Dagger = Captain Claw Beard (Suchomimus)

Armored Knights = Maverick (Titanoceratops)

Red Lambeosaur = Karen (Lambeosaurus)

Wyvern Fang = Draco (Tyrannosaurus)

I also have possession of the Dark Guild: 

Gigiyas Clan = Moebius (Giganotosaurus)

If you want a spot as a guild master, let me know so I'll save a spot for you!