A busy time at the beach: multiple examples of gregarious dinosaur behaviour inferred from a set of trackways from the Late Cretaceous of Alberta, Canada

A diverse collection of dinosaur tracks and trackways preserved on a single bedding plane record activities of many animals over a very short time, possibly just a few days or less. The assemblage is exposed on a detached slab of siltstone from the Campanian–Maastrichtian St. Mary River Formation in southwestern Alberta, Canada. Members of four different groups of dinosaurs are identified as the makers of either isolated tracks, or trackways of varying lengths, and include inferred hatchling tyrannosaurids, medium and large ornithomimids, small and medium-sized ornithopods, and a small hadrosaurid. All but one of the seven trackways attributed to hatchling tyrannosaurids occur as codirectional, equally spaced pairs, but one pair walked in the opposite direction, albeit parallel, to the other two. The pair of ornithomimid trackways also appears to represent two animals walking at the same speed, in the same direction, and turning together. The trackway attributed to a medium-sized biped, possibly Parksosaurus warreni, is the first evidence for the presence of these dinosaurs in the environment recorded by the St. Mary River Formation.