The Scenario

This image represents a 75-million-year-old scene from an area around what is now southeast Alberta, Canada. The focal point of this scene involves a confrontation in the middle of a dry stream bed in which an armored dinosaur, Euoplocephalus, tries to fend off the attack of a tyrannosaur, Albertosaurus, with its bony tail club. Keeping a wary eye on the fight is the ornithomimid Struthiomimus, content to try to find a spot to eat a recently caught meal consisting of a small mammal. On the far bank of the stream, small groups of the crested hadrosaur Corythosaurus and the spike-frilled ceratopsian Styracosaurus beat a hasty retreat from the conflict.

The Environment

The fossils are contained in a rock unit called the Judith River Formation. The fine sand, silt, and mud that makes up this rock unit were washed out of the ancestral Rocky Mountains to the west. Meandering rivers transported the eroded debris across a broad flood plain and emptied through a large delta into a shallow continental sea whose shoreline ran along the present border between Alberta and Saskatchewan. Floods were common during the wetter parts of the year and during peak runoff in the mountains. Although a cool dry season occurred, the climate was frost-free, and the air was probably often humid. The lowland forests were dominated by cypress and redwoods, with ferns providing a major portion of the ground cover. Cattails and water lilies grew in and along the lakes and ponds adjacent to the streams.