Page "Albertosaurus" Paragraph 15

All identifiable fossils of Albertosaurus sarcophagus are known from the upper Horseshoe Canyon Formation in Alberta.

These younger units of this geologic formation date to the early Maastrichtian stage of the Late Cretaceous Period, 70 to 68 Ma ( million years ago ).

Immediately below this formation is the Bearpaw Shale, a marine formation representing a section of the Western Interior Seaway.

The seaway was receding as the climate cooled and sea levels subsided towards the end of the Cretaceous, exposing land that had previously been underwater.

It was not a smooth process, however, and the seaway would periodically rise to cover parts of the region throughout Horseshoe Canyon times before finally receding altogether in the years after.

Due to the changing sea levels, many different environments are represented in the Horseshoe Canyon Formation, including offshore and near-shore marine habitats and coastal habitats like lagoons, estuaries and tidal flats.

Numerous coal seams represent ancient peat swamps.

Like most of the other vertebrate fossils from the formation, Albertosaurus remains are found in deposits laid down in the deltas and floodplains of large rivers during the later half of Horseshoe Canyon times.