Dakotaraptor

***Dakotaraptor*** (meaning “thief from Dakota”) is a potentially chimaeric genus of large dromaeosaurid theropod dinosaur that lived in North America during the Late Cretaceous period. The remains have been found in the Maastrichtian stage of the Hell Creek Formation, dated to the very end of the Mesozoic era, making *Dakotaraptor* one of the last surviving dromaeosaurids. The remains of *D. steini* were discovered in a multi-species bonebed. Elements of the holotype and referred specimens were later found to belong to trionychid turtles, and further analysis of potential non-dromaeosaurid affinities of the holotype and referred material have not yet been conducted. Phylogenetic analyses of *D. steini* place it in a variety of positions in the Dromaeosauridae.

## Description

### Size

*Dakotaraptor* is exceptionally large for a dromaeosaurid; it has an estimated adult length of 5.5 m (18 ft). In 2016 other estimations suggested a length of 4.35-6 m (14.3-19.7 ft) in length and 220-350 kg (485-772 lbs) in weight.

This approaches the size of one of the largest known dromaeosaurids, *Utahraptor*. *Dakotaraptor* however, does not have the proportions and adaptations of *Utahraptor*, but more closely resembles smaller dromaeosaurids like *Deinonychus*.

### Distinguishing traits

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 5 millimetres (0.20 in) on the rear edges and twenty to twenty-seven denticles on the front edges.

### Skeleton

#### Vertebral column

The vertebrae of the back are highly pneumatised, filled with trabecular bone that shows many air spaces. On the middle tail vertebrae the front joint processes, the prezygapophyses, are extremely elongated with an estimated intact length of 70 centimetres (28 in), spanning about ten vertebrae. This stiffens the tail.

#### Forelimb

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.* proposed 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 centimetres (14 in) long and the other lower arm bone, the radius, measures 32 centimetres (13 in). The hand bones show that their joints allowed for little mobility. The wingspan of *Dakotaraptor* was estimated at 120 centimetres (47 in), 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.

#### Hindlimb

Overall, the hindlimb is built lightly and with long elements, contrary to the robust, stocky hind limbs of *Utahraptor*. *Dakotaraptor* more closely resembles the agile, springy smaller dromaeosaurids and would have been well-suited to running and pursuit predation. The length of the thighbone is 558 millimetres (22.0 in). It is relatively shorter and more lightly built than that of *Utahraptor*. To the contrary the shinbone is rather elongated. The holotype shinbone is, with a length of 678 millimetres (26.7 in), the longest dromaeosaurid tibia known. It is 22% longer than the thighbone, indicating a good running capability. The shinbone's cnemial crest has a sharp corner pointing to the front. Its fibular crest ends in a hook-shaped process pointing to above, a condition that is unique in the entire Theropoda. The astragalus and calcaneum, the upper ankle bones, are fused just as in *Bambiraptor*. The top of the calcaneum has but a small contact facet for the calfbone, indicating that this fibula must have had a very narrow lower end. The metatarsus has an estimated length of 32 centimetres (13 in), which makes it rather long relative to the remainder of the hindlimb.

The foot claws of *Dakotaraptor* include a typical dromaeosaurid raptorial second claw, or "sickle claw", which was used for killing or holding down prey. It is large and robust with a diameter of 16 centimetres (6.3 in) and a length of 24 centimetres (9.4 in) measured along the outer curve. This equals 29% of the length of the thighbone, compared to 23% in *Deinonychus*. The claw is transversely flattened and has a droplet-shaped cross-section. The flexor tubercle, a large bump near the base, served as an attachment site for flexor muscles - the larger it was, the greater the slashing strength. *Dakotaraptor* has a flexor tubercle that is larger relative to overall claw size than it is in other discovered dromaeosaurids, potentially giving it the strongest slashing strength of any known member of this group. The flexor tubercle on the third claw of the foot is almost non-existent, very reduced in size compared to other dromaeosaurids, suggesting a more minimized use of that claw. As these are the bony cores of the claws, they would have been covered in a keratinous sheath that extended the "nail" and ended in a sharp tip. The third claw too is keeled but is much smaller with a tip to joint length of 7 centimetres (2.8 in) and a curve length of 9 centimetres (3.5 in). The groove on its outer side towards the tip ends in a bone tunnel, a rare condition.

## *Dakotaraptor* in The Amazing Dinosaur Adventure

A stampede of *Dakotaraptor* from the opening narration to *The Wisdom of Friends*