On another note, you did mention Giganotosaurus. Are you a post-2019 player? If yes, then some Common, Rare, Super Rare and regular Legendary creatures have been removed from Battle Stages.
Some of these have special events. For your convenience I have listed those here.
Common : Labyrinthodontia, Bonitasaura, Utahraptor, Hatzegopteryx
Rare : Carnotaurus, Monolophosaurus, Gallimimus, Rhamphorhynchus
Super Rare : Spinosaurus, Ankylosaurus, Quetzalcoatlus, Kaprosuchus
Legendary : Ostafrikasaurus, Microposaurus, Dimorphodon, Therizinosaurus
The same Rarity creatures without unlock events as of now (Post Reshuffle) are as follow.
Common : Tuojiangosaurus, Coloborhynchus, Pelecanimimus
Rare : Allosaurus, Giganotosaurus, Pyroraptor, Nasutoceratops, Tyrannotitan
Super Rare : Rajasaurus, Metriorhynchus, Aerotitan, Supersaurus
Legendary : Suchomimus, Sarcosuchus, Prionosuchus, Dimetrodon, Scaphognathus, Shunosaurus
Shunosaurus and Supersaurus however are unlockable via Bracketed Tournaments depending on your Park level.