Hesperosaurus vs. Stegoceras
The seaside woodland of what’s now the lower Morrison Formation, 156 million years ago. Over the next few million years, this ecosystem will evolve into a dry, arid fern savannah. Now, however, it’s a muddy coastline at the edge of the slowly receding Sundance Sea.
A goat-sized pacycephalosaur Stegoceras wanders through this subtropical woodland. At first glance, it’s not terribly different from this dinosaur’s regular home in the shoreline bayous of late Cretaceous Alberta along the Bearpaw Sea. Insects drone in the air, turtles and crocodiles bask on the mud flats, and the damp ground has thick patches of horsetails under a canopy of cycads and tree ferns. But the plants and animals all look a little different, and the air is filled with foreign smells. The Stegoceras feels uneasy, and glances around as he wanders this world that existed 80 million years before his species evolved.
Suddenly the Stegoceras detects the movement of large animals nearby. Instinct drives him to get out of the way of big dinosaurs as they plowed through the woodlands, and both large herbivores and carnivores are no stranger to Stegoceras. He looks around for a place to hide, his dome-shaped head swiveling on his muscular neck.
Stegoceras quickly notices a hollow under an old tree root, and wriggles inside. Just as he gets in cover, a pair of Hesperosaurus come into view, plodding slowly through the bush. These stegosaurs are actually a breeding pair, and can be told apart by the bony plates on their backs- the males are low and round with vibrant colour patterns, while the female’s plates are narrow, dark, and pointed at the tips (Saitta, 2015). The pair are nearing the hiding spot of Stegoceras, although they don’t know it.
For a relatively small dinosaur, Stegoceras is tough. Having never seen a stegosaur before, he doesn’t know whether these odd dinosaurs are harmless or not, but he doesn’t want to risk letting them get any closer. Stegoceras growls and grunts as loud as he can at the unaware Hesperosaurus pair, and kicks dirt at them with his hind legs. The Hesperosaurus are startled to notice this small but determined critter below them.
Stegoceras keeps up the defence, thumping his stiff tail on the ground and presenting the two Hesperosaurus with the top of his head, which bears a bony ram on top surrounded by rough little spines. The Hesperosaurus have never seen anything like this before, and decide to leave this defensive little dinosaur alone. Together they turn around and vanish into the scrubby thickets.
Stegoceras follows them a short ways out of his hiding spot, grunting and puffing his throat out to look intimidating. Despite the size difference, his scare tactic has successfully repelled the Hesperosaurus pair.