The Late Jurassic Morrison Formation. Giant sauropods roam the fern parties, the fearsome Allosaurus and Torvosaurus lurk in the woods alongside them, and one of the most pugnacious creatures nature has seen up to this point acts as a boundary between the two. Though they are solitary, males will sometimes congregate with females during the breeding season. Their plates are larger than females', so they seem far more intimidating to both predators and rival males.