Name means: Chasm Reptile
Species: belli, russelli
Range: Late Cretaceous (Santonian-Campanian, 85-70 MYA) from Montana and Alberta, Canada
Size estimate: 14-16 ft length, 1.5-2 tons
Discovery: Lawrence Lambe, 1914
Classification: dinosauria, ornithischia, cerapoda, ceratopsia, chasmosauridae
The horned dinosaurs belong to two basic groups. The centrosaurs had short frills and long nose horns. The chasmosaurs had long frills and short nose horns. Chasmosaurus lends its name to the long-frilled ceratopsians. It earned that name because of its own frill. Though it looks solid, the bony parts frame two large holes or “chasms” in the frill. This kept the skull light. Scientists used to think that horned dinosaur frills helped protect their necks like shields. Holes in a shield don’t make much sense, though. While the frills might not have acted like armor, they could have protected the animal in other ways. When Chasmosaurus lowered its head to charge, the frill would make the animal look twice as big. An illusion like this could intimidate an attacker and prevent a fight. Ceratopsian frills also have arrangements of horns and other decorations unique to each species. This might have helped coordinate herds the way flags help coordinate armies. Fossils of a baby Chasmosaurus show that these frills started small, but grew as the animal reached maturity. This is why the young Chasmosaurus has a slightly different frill than the adult on the ridge.
Chasmosaurus lived at a time when a sea covered the Great Plains and turned western North America into a long, skinny landmass called Laramidia. This sea changed levels many times during the Cretaceous and might explain Chasmosaurus’ limited range. It may also explain why large horned dinosaurs had such a variety of frill shapes and horns, and why they only occurred in Laramidia. When the sea level rose, it would isolate horned dinosaur populations. Each population then developed new horn arrangements over generations. When the sea levels fell, different species would compete with each other as they spread out. Some would go extinct, while others would move into new territory. Then the process would begin again.