Albertosaurus - Paleoecology

Paleoecology

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.

The fauna of the Horseshoe Canyon Formation is well-known, as vertebrate fossils, including those of dinosaurs, are quite common. Sharks, rays, sturgeons, bowfins, gars and the gar-like Aspidorhynchus made up the fish fauna. Mammals included multituberculates and the marsupial Didelphodon. The saltwater plesiosaur Leurospondylus has been found in marine sediments in the Horseshoe Canyon, while freshwater environments were populated by turtles, Champsosaurus, and crocodilians like Leidyosuchus and Stangerochampsa. Dinosaurs dominate the fauna, especially hadrosaurs, which make up half of all dinosaurs known, including the genera Edmontosaurus, Saurolophus and Hypacrosaurus. Ceratopsians and ornithomimids were also very common, together making up another third of the known fauna. Along with much rarer ankylosaurians and pachycephalosaurs, all of these animals would have been prey for a diverse array of carnivorous theropods, including troodontids, dromaeosaurids, and caenagnathids. Intermingled with the Albertosaurus remains of the Dry Island bonebed, the bones of the small theropod Albertonykus were found. Adult Albertosaurus were the apex predators in this environment, with intermediate niches possibly filled by juvenile albertosaurs.