A 73-million-year-old shoreline
The rocks in the Bowdoin Canyon area belong to the Wapiti Formation, a sequence of sandstones, mudstones, and coals laid down between 80 and 68 million years ago. During the Late Cretaceous Period, this region was a vast coastal floodplain, with rivers carrying sediment from the newly rising Rocky Mountains to the west. The fine-grained siltstones and sandstones of this ancient river system were perfect for preserving the delicate impressions of animal feet.
The trace fossils here reveal a surprising picture of pterosaur locomotion. Pterosaurs, the flying reptiles of the Mesozoic, were long thought to be clumsy on the ground. The trackways, identified by the ichnogenus Pteraichnus, show a very different story. These animals walked using all four limbs. The tracks consist of three-toed hand prints (manus) and four-toed foot prints (pes). The arrangement proves the pterosaurs used an erect, quadrupedal gait, planting their feet and the knuckles of their folded wings on the ground to move efficiently. One large isolated hand print measures 25.5 cm in length, suggesting a trackmaker with an estimated wingspan of 7.7 meters.
Footprints of ancient birds
Alongside the pterosaur tracks, the site contains thousands of much smaller footprints. These belong to the ichnospecies Aquatilavipes swiboldae, a type of track left by a small, shorebird-like animal about the size of a modern sandpiper. These avian tracks are exceptionally rare and provide direct evidence of behavior.
Many of the trackways show the birds probing the soft mud with their beaks, likely searching for worms, crustaceans, and other invertebrates along the water's edge. This is a snapshot of feeding behavior from over 72 million years ago. The sheer density of tracks at sites like Tyrants Aisle, another locality within the Wapiti Formation, suggests these riverbanks were popular feeding grounds. Together, the bird and pterosaur tracks record a living ecosystem. Ichnology—the study of trace fossils—records the animals that were present, and how they moved through and interacted with their environment. The Wapiti Formation also contains skeletal fossils of hadrosaurs, tyrannosaurs, and ankylosaurs, filling out the picture of this high-latitude Cretaceous world.