It’s the mating season for Stegosaurus ungulatus in Late Jurassic North America, and these two bulls are challenging one another for the cows’ affection. We always see Stegosaurus using its tail spikes (or “thagomizer”) against predators such as Allosaurus or Ceratosaurus, but it seems logical to me that it might have used them in fights with other stegosaurs as well.