Fragmentary skull of Atrociraptor
- Alberta, Canada ( Horseshoe Canyon Formation)
- Atrociraptor marshalli
Atrociraptor was a genus of carnivorous dinosaur from the group of Dromaeosauridae. So far, a fragmentary skull is only known that was discovered in the Horseshoe Canyon Formation of Alberta (Canada) and is dated to the Late Cretaceous (late Campanian to early Maastrichtian ).
Atrociraptor reached a length of about 1.8 meters.
The found fragmentary skull consists of the right upper jaw ( maxilla ), the rather complete right dentary ( the tooth-bearing part of the mandible ), parts of the left dentary, premaxillary two legs ( premaxilla ) and numerous bone fragments. Unlike other Dromaeosauriden the skull was unusually short and high. Thus the main body of sitting in front of the upper jaw premaxillary bone was higher than it is wide, similar to Deinonychus. The teeth were more bent backward than other Dromaeosauriden except Bambiraptor and Deinonychus. The teeth of the upper jaw were all about the same. In addition, the Maxillarfenster was greater than in other Dromaeosauriden and directly above the Promaxillarfenster located, whereas it was higher for all other Dromaeosauriden behind the latter.
The teeth were flat and sound like, the teeth of the lower jaw were generally smaller than those of the upper jaw. The denticles ( teeth ) were larger on the rear cutting edge of the teeth and less numerous than on the front cutting edge, similar to other Dromaeosauriden. In Zwischenkieferbein sat on each side four teeth, as with other Dromaeosauriden. Each maxilla contributed 11 teeth. The number of teeth in the lower jaw can not be accurately determined, estimated, however, each mandible was 14 teeth. Overall Atrociraptor was thus probably 58 teeth. The upper jaw (maxilla ) is obtained in a length of 9.2 cm and a height of 4.5 cm, of which the tooth row represents 8.5 cm. Thus, the upper jaw is just like the Zwischenkieferbein deeper than other Dromaeosauriden.
Currie and Varicchio studied in their first description of Atrociraptor the relationships of the new genus, based on skull characteristics. They came to the conclusion that Atrociraptor was most closely related to Deinonychus and second closest with Bambi Raptor, and arranged Atrociraptor within the Velociraptorinae a, a subset of Dromaeosauridae. This association is based on the denticles smaller on the front side of the teeth than at the back. However, a recent study by Currie and Rich Long (2009) classified Atrociraptor together with Saurornitholestes and Bambiraptor within in a new group, the Saurornitholestinae.
History of discovery and naming
The Fund ( holotype, specimen number TMP 95.166.1 ) was discovered in 1995 by Wayne Marshall and dissected by Ken Kucher from the Royal Tyrrell Museum of Palaeontology. Marshall discovered jaw and tooth fragments in a hillside, about five kilometers west of the Royal Tyrrell Museum of Palaeontology in Drumheller. The find was in a relatively hard, isolated block of sandstone, which was surrounded by softer sands. The site is located approximately five feet above the Daly - coal seam number 7 Atrociraptor was described in 2004 by Phillip Currie and David Varricchio scientifically. The name Atrociraptor derives from the Latin words atroci - " cruel, brutal" and raptor " robber " from. The species name honors marshalli Wayne Marshall, the discoverer of the skull.