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Dakotaraptor is a genus of large, carnivorous dromaeosaurid theropods from the Late Cretaceous of North America. They have been found in the Maastrichtian-age [ell Creek Formation, dated to the very end of the Cretaceous period, making Dakotaraptor one of the last surviving dromaeosaurids.

Dakotaraptor was about 5.5 meters (eighteen feet) long, which makes it one of the largest dromaeosaurids known. It had long arms with one of the lower arm bones shows quill knobs, demonstrating that it was most likely feathered. It also had long rear legs with a very large sickle claw on the second toe; this claw could be used to kill relatively large plant-eating dinosaurs. It lived in the same time and area as many iconic late Cretaceous dinosaurs such as Ankylosaurus, Triceratops, and Tyrannosaurus.

Description

Size

Dakotaraptor is exceptionally large for a dromaeosaurid; it has an estimated adult length of 18 feet, or 5.5 meters.< 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.

Forelimbs and feathers

Like virtually all other theropods, Dakotaraptor likely possessed a furcula, or “wishbone”, as part of the shoulder girdle. Theropod wishbones are quite varied and often different from the strongly U-shaped furculae most modern birds possess; the elements originally identified as the furcula of Dakotaraptor were U- to V-shaped, similar to many other dromaeosaurids such as Velociraptor, and even the large spinosaurid theropod Suchomimus. In 2015, a study by Victoria Megan Arbour] et al. hypothesized that the presumed Dakotaraptor furculae in fact represented a part of a turtle armour, the entoplastron of Axestemys splendida, a member of the Trionychidae. In 2016, DePalma et al. recognized that none of the referred furculae actually belonged to Dakotaraptor, and excluded them from its hypodigm.

The wing of Dakotaraptor was given much attention in the describing article. Here, “wing” is used as an anatomical descriptive term not related to its functionality, since Dakotaraptor was flightless. This is similar to the term “wing” for the same appendages in ostriches, emus, and other flightless birds. It is meant to express that arm is equipped with long feathers. Many of the wing bones were discovered (humerus, radius, ulna, two of the three metacarpal wrist bones, and parts of the finger digits), so the wing is very complete. The humerus, the upper arm bone, is relatively long and slender. It is somewhat bent to the inside. The most notable anatomical feature is the row of very prominent bumps along a ridge on the lower edge of the ulna, one of the forearm bones. These are called ulnar papillae, or quill knobs. In birds and some other theropod dinosaurs, these bumps were spots for reinforced attachment of the remiges, or wing feathers. When quill knobs are present, this is considered a strong indication that the animal had long remiges on the wings. Since quill knobs are rare in the fossil record, paleontologists mainly relied on phylogenetic bracketing to determine if a species was likely to have had wing feathers - if a relative on a "higher" branch of the evolutionary tree had the feathers, and one on a "lower" branch down had them also, then a species in the middle position likely did as well. Dakotaraptor’s quill knobs show that the animal unequivocally had prominent wing feathers, making it the largest dromaeosaurid with confirmed plumage of that type. The quill knobs of Dakotaraptor have a diameter of about 8–10 millimetres (0.31–0.39 in), which shows that these feathers were rather large. It was estimated that a complete series might include fifteen of these papillae ulnares. The ulna is 36 centimeters (14 in) long and the other lower arm bone, the radius, measures 32 centimeters 13. The hand bones show that their joints allowed for little mobility. The wingspan of Dakotaraptor was estimated at 120 centimeters (47 inches), not taking into account possible primary remiges longer than the hand.

The second metacarpal of the metacarpus of the hand, the bone that primary remiges attach to, also had a flat bony shelf as its dorsal surface. The shelf made a perfect spot for the primary feathers to lay across in their life-attachment.

Phylogeny

Dakotaraptor was placed in the Dromaeosauridae. A cladistic analysis showed that it was the sister species of Dromaeosaurus. They again formed a clade with Utahraptor, of which clade Achillobator was the direct side branch. Despite being related to other gigantic dromaeosaurids, Dakotaraptor was suggested to represent a separate fourth instance of dromaeosaurid size increase, besides Deinonychus, Unenlagia, and the Achillobator plus Utahraptor clade.

Possible synonymy with Acheroraptor

Acheroraptor temertyorum is another theropod from the Hell Creek Formation, named in 2013 for a lower jaw, a maxilla, and some teeth. Acheroraptor was diagnosed by multiple features, including the possession of ridges on the teeth. Teeth are the only overlapping features between Acheroraptor and Dakotaraptor. However Acheroraptor is significantly smaller, and differs from Dakotaraptor only in that it possesses vertical ridges on the teeth crowns. Andrea Cau noted that though Dakotaraptor is known from individuals of differing sizes, some of the smaller specimens are also fully mature, and it is possible that the size difference means Dakotaraptor is simply a different species or size morph of Acheroraptor. A phylogenetic analysis presented by Cau, though relying on fragmentary specimens, did not result in a close relationship between the two.

Paleobiology

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 6–9 meters (20–30 ft) 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

Thorn, Dakota, Lorenzo, Xavier, Flavia, Cheramie, and Farrell  in The Land Before Time XXI: Hunter Valley, The Land Before Time XXV: The Four Kinds Quest, and The Land Before Time: The Next Generation are Dakotaraptor.

References