Hell Creek Formation
Several larger skeletons from the early Maastrichtian Horseshoe Canyon Formation of Alberta and the late Maastrichtian Hell Creek Formation of Montana and South Dakota have been referred to "Chirostenotes" in the past, though more recent studies concluded that they represent several new species. The Horseshore Canyon formation specimen was renamed "Epichirostenotes" in 2011, while the Hell Creek Formation specimens have been referred to the genus "Anzu".