Alberta Tyrannosaurs: Species, Formations & Geological Ages
Theropods are a broad group of carnivorous dinosaurs that includes both large predators and smaller “raptor”-type dinosaurs. Within Theropoda is the family Tyrannosauridae, commonly called tyrannosaurs.
Tyrannosaurus rex is one species within this family, but Alberta’s tyrannosaurs also include Albertosaurus, Gorgosaurus and Daspletosaurus. In other words, not all tyrannosaurs are T. rex, although T. rex is a tyrannosaur.
These animals did not all live at the same time. Gorgosaurus (formely know as Albertosaurus libratus) and Daspletosaurus overlapped in age, while the others occur in different geological intervals. This is one reason locality and rock formation are so important when identifying isolated tyrannosaur teeth.
The table below compares four major tyrannosaurs represented in Alberta, including their relationships, geological formations and ages.
Alberta Tyrannosaurs
| Comparison | Tyrannosaurus rex | Albertosaurus sarcophagus | Gorgosaurus | Daspletosaurus |
|---|---|---|---|---|
| Theropod family | Tyrannosauridae | Tyrannosauridae | Tyrannosauridae | Tyrannosauridae |
| Theropod subfamily | Tyrannosaurinae | Albertosaurinae | Albertosaurinae | Tyrannosaurinae |
| Build | Heavy, muscular | Slender, agile | Slender, agile | Heavy, muscular |
| Time period | Late Cretaceous | Late Cretaceous | Late Cretaceous | Late Cretaceous |
| Alberta rock formation | Scollard Formation (lower member) | Horseshoe Canyon Formation (Edmonton Group) | Dinosaur Park & Oldman formations (Belly River Group) | Dinosaur Park & Oldman formations (Belly River Group) |
| Formation age | 66.04–66.88 million years ago | 68–73.1 million years ago | 74.8–77.5 million years ago | 74.8–77.5 million years ago |
| Approx. Montana equivalent | Hell Creek Formation | St. Mary River Formation | Judith River & Two Medicine formations | Judith River & Two Medicine formations |
Why Formation Matters When Identifying Tyrannosaur Teeth
Isolated tyrannosaur teeth can be difficult to identify confidently to genus or species from morphology alone. Tooth position, age of the animal, wear and preservation can all affect appearance.
Geological context can therefore provide critical supporting evidence. A tooth from the Horseshoe Canyon Formation near Drumheller comes from a different fauna and age than one from the older Dinosaur Park or Oldman formations.
This guide is intended as a general reference. Individual identifications should consider the specimen itself, its locality, formation and documented provenance.