Photo by Emily Willoughby at the Royal Tyrell Museum
In 1995 Wayne Marshall of East Coulee, Alberta discovered what was to become the type and only specimen of a dromaeosaurid known, 9 years later thanks to Philip J. Currie and David J. Varricchio, today as Atrociraptor marshalli. The Horseshoe Canyon Formation where the fossil was discovered is the home of many Albertosaurus fossils as well. Originally assigned to the Velociraptorinae in the Dromaeosauridae; however, in 2009 Currie assigned Atrociraptor to the Saurornitholestinae. Despite the minimal nature of the fossil remains, the snout and a small amount of skull make up the type specimen, the fenestrations that are in the snout are unique enough that the specimen is known to be different enough from other members of the Saurornitholestinae to constitute remaining classified as a unique species and not synonymized with any other taxa.