Around the late Jurassic and the Cretaceous period is when the big boy, predatory carnivores started to rule the land. The Cretaceous period is also the main era when herbivores started to develop their protective armor against predators. It's up to Kaga, but the Triassic period isn't the most compelling, because the smaller dinos during that time aren't as much of a threat. Though, it doesn't matter to me if all three main dino era's will be in the role play.