Albertosaurus (Dinosauria: Theropoda) material from an Edmontosaurus bonebed (Horseshoe Canyon Formation) near Edmonton: clarification of palaeogeographic distribution

Abstract

Tyrannosaurid cranial bones — including a maxilla, dentary, and pterygoid — were collected from a monodominant Edmontosaurus bonebed in the Horseshoe Canyon Formation exposed near the city of Edmonton, Alberta, Canada. The maxilla can be identified as Albertosaurus sarcophagus based on the narrow interfenestral strut and relatively deep dental pits along the length of the palatal shelf. Cranial bones are interpreted to have come from a single large individual that was incorporated into the site during, or temporally close to, the formation of the final taphocoenosis. This discovery constitutes the northernmost record of A. sarcophagus, and helps to narrow the geographic gap of latest Cretaceous tyrannosaurs between Alberta and Alaska. The geographic distribution of A. sarcophagus — eclipsed only in areal extent by Tyrannosaurus rex in North America — attests to the adaptability of this species, which endured regional changes in climate that forced extirpation of many ornithischian taxa during deposition of the Horseshoe Canyon Formation.