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The first fossils of Dakotaraptor were found in South Dakota, USA, in 2005. In 2015, the genus Dakotaraptor received its name, meaning "plunderer of Dakota", when the type species Dakotaraptor steini was described. The fossils contain an incomplete skeleton without a skull and some individual bones. They have been found in the Maastrichtian-age Hell Creek Formation, dated to the very end of the Cretaceous period, makingDakotaraptor one of the last surviving dromaeosaurids.
Dakotaraptor was about five to six metres long, which makes it one of the largest dromaeosaurids known. It had long arms. One of the lower arm bones shows bumps for feathers, proving that Dakotaraptor was feathered. It also had long rear legs with a very large sickle claw on the second toe. The claw could be used to kill relatively large plant-eating dinosaurs. Dakotaraptor lived in the same time and area as Tyrannosaurus rex.
In 2005, paleontologist Robert DePalma in Harding County, South Dakota discovered the skeleton of a large dromaeosaurid. Subsequently, the same site produced additional dromaeosaurid remains, as well as abundant other fossils in 2010 described by DePalma in his master's thesis. In 2015, the type species Dakotaraptor steini was named and described by Robert A. DePalma, David A. Burnham, Larry Dean Martin, Peter Lars Larson and Robert Thomas Bakker. The generic name combines a reference to South Dakota and the Dakota people with a Latin raptor, "plunderer". The specific name honours paleontologist Walter W. Stein. Dakotaraptor was one of eighteen dinosaur taxa from 2015 to be described in open access or free-to-read journals.
The holotype, PBMNH.P.10.113.T, was found in a sandstone layer of the upper Hell Creek Formation, dating from the late Maastrichtian. It consists of a partial skeleton, lacking the skull, of an adult individual. It contains a piece of a back vertebra, ten tail vertebrae, a furcula, both upper arm bones, both ulnae, both radii, the first and second right metacarpals, three claws of the left hand, a right thighbone, both shinbones, a left astragalus bone, a left calcaneum, the left second, third and fourth metatarsal, the right fourth metatarsal, and the second and third claw of the right foot. Apart from the remains of the holotype, in the site bones were discovered that also belonged to Dakotaraptor but which represented a more gracile morph. These included the specimens PBMNH.P.10.115.T: a right shinbone; PBMNH.P.10.118.T: a connected left astragalus and calcaneum; and KUVP 152429: a furcula. Additionally four isolated teeth were referred, specimens PBMNH.P.10.119.T, PBMNH.P.10.121.T, PBMNH.P.10.122.T, and PBMNH.P.10.124.T. These fossils are part of the collection of The Palm Beach Museum of Natural History. Other referred fossils are NCSM 13170, a furcula, and KUVP 156045, an isolated tooth.
Dakotaraptor is exceptionally large for a dromaeosaurid; it has an estimated adult length of 5.5 m (18 ft). This approaches the size of the largest known dromaeosaurid, Utahraptor. Dakotaraptor however, does not have the proportions and adaptations of Utahraptor, but more closely resembles smaller dromaeosaurids like Deinonychus.
Apart from the large size, the description of 2015 indicated some additional distinguishing traits. On the fourth foot claw, the boss that serves as an attachment for the tendon of the flexor muscle is reduced in size. The "blood groove" on the outer side of the fourth claw of the foot, towards the tip is fully enclosed over half of its length, forming a bony tubular structure. The second and third claws of the foot have sharp keels at their undersides. The second foot claw, the "sickle claw", equals 29% of the thighbone length. On the shinbone, the crista fibularis, the crest that contacts the calfbone, is long and lightly built with a height that does not exceed 9% of the crest length. The upper edge of this crest ends in a hook. On the second metacarpal, of the two condyles that contact the finger, the inner one is almost as large as the outer one. The outer side of the second metacarpal has but a shallow groove for the ligament that connects it to the third metacarpal. When the arm is seen in a flat position, of the second metacarpal the edge between the wrist joint and the upper shaft is straight in top view. The teeth have fifteen to twenty denticles per five millimetres on the rear edges and twenty to twenty-seven denticles on the front edges.
Dakotaraptor is the first medium-sized predator discovered in the Hell Creek Formation, intermediate in length between gigantic tyrannosaurids like Tyrannosaurus and smaller deinonychosaurians like Acheroraptor.Especially if it was a pack-hunter, cooperating in groups, it could have preyed upon larger herbivores, possibly competing with subadult tyrannosaurids in the six to nine metres length range. As its shinbone was longer than its thighbone, Dakotaraptor would have had a good running capacity, filling the niche of pursuit predator. The keeled claw of the second toe, the "sickle claw", was used to bring down prey and had a more robust flexor tubercle than that of Utahraptor. To the contrary, the third foot claw was relatively smaller in size than with other dromaeosaurids and seems not to have had an important function in attacking prey animals. Two morphs, a robust and a gracile one, were present in the fossil material. A study of the bone histology showed that both morphs were adult, so the lighter build of some bones was not caused by a young age. Individual variety or pathologies might account for the difference but the simplest explanation is sexual dimorphism. It can as yet not be deduced which morph was male and which female. On the ulna of the lower arm, wide papillae ulnares or quill knobs are present, attachment points for large pennaceous feathers. Adult Dakotaraptor individuals were much too heavy to fly. Despite this flightless condition, the feathers were not reduced. There is a variety of possible alternative functions for its wings, including shielding of eggs, display, intimidation and keeping balance while pinning down prey with the sickle claw. These functions however, do not necessitate quill knobs and the describing authors considered it likely that Dakotaraptor descended from a smaller flying ancestor which had them.
Dakotaraptor in Land Before Time
Lorenzo, Darrien, Flavia, Thorn, Farrell, Dakota, and Xavier were Dakotaraptors. They appear in The Land Before Time XXI: Hunter Valley and also in The Greatest Adventure trilogy. They are part of the Fast Biter category.