The lower gate should be the only one to open by releasing the Homalocephale since it's small herbivore size
When you release the other dinosaurs coming out of the lower gate.
Dracorex, Stygimoloch, Archaeornithomimus, Struthomimus, Troodon, Velociraptor, Dryosaurus, Dilophosaurus, Gallimimus, Deinonychus, Herrerasaurus, Nodosaurus, Polacanthus, Proceratosaurus and the Sauropelta are all the ones that come out with the lower gate
When you release the other dinosaurs coming out of the lower gate.
Dracorex, Stygimoloch, Archaeornithomimus, Struthomimus, Troodon, Velociraptor, Dryosaurus, Dilophosaurus, Gallimimus, Deinonychus, Herrerasaurus, Nodosaurus, Polacanthus, Proceratosaurus and the Sauropelta are all the ones that come out with the lower gate