Dakotaraptor

Credit: R.J. Palmer.

*Dakotaraptor* is a genus of potentially chimeric, dromaeosaurid dinosaur that lived in the Montana during the Late Cretaceous.

## History

Robert DePalma (2005) found a fluvial bonebed, finding a large dromaeosaur skeleton among dinosaurian and other other animal remains. He later returned and found more. In 2015 DePalma described the specimen, assigning PBMNH.P.10.113.T, a partial dorsal, 10 caudals, humeri, ulnae, radii, the 1st and 2nd right metacarpals, 3 claws of the left hand, the right thighbone, both sinbones, the left astragalus, the left calcaneum, the left 2nd, 3rd and 4th metatarsal, the right 4th metatarsal and the 2nd and 3rd claw of the right foot, as the holotype; later, a furcula was assigned, but later excluded due to being from a turtle rather than a dinosaur. A gracile morph is also present. These include right shinbone PBMNH.P.10.115.T; articulate left astragalus and calcaneum PBMNH.P.10.118.T; and "furcula" KUVP 152429, which was found to belong to a trionychid turtle. 4 isolate teeth, PBMNH.P.10.119.T, PBMNH.P.10.121.T, PBMNH.P.10.122.T and PBMNH.P.10.124.T were also referred.

*Dakotaraptor* may be a different species or "size-morph" of *Acheroraptor*, due to them being so much larger than adult *Acheroraptor* specimens. Phylogenetic tests show that the two fossils of *Dakotaraptor* and *Acheroraptor* are not related closely.

## Description

Autapomorphies are: a reduced flexor muscle that anchors to a boss on the fourth foot claw; the fourth foot claw has a blood groove on the outer surface, with half of the tip fully enclosed and forming a bony tube: sharp heels during on the undersides of the second and third claws of the foot; the second sickle claw equaling 29% of the thighbones length: the crista fibularis is elongate and light, having a height that does not exceed 9% of the crests length, with the upper edge of the crista fibularis ending in a hook; the second metacarpal having an inner condyle almost larger than the outer; the outer surface of the second metacarpal bears a shallow groove that anchors the ligament which connects the third metacarpal: the arm has a second metacarpal that bears an edge between the wrist and upper shaft that is straight in the top, with this feature only seen when in the flat view; teeth with 15-20 denticles/5 millimeters (0.20 in) on the rear edges and twenty to twenty-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; and the teeth have fifteen to twenty denticles per 5 millimeters (0.2 inches) at the rear edges and 20-27 denticles on the front. The skeletal mount displays created for the 2021 Yokohoma exhibition are 180 centimeters tall.

The vertebrae are very pneumatised. The prezygapophyses of the mid casuals are very tall, with the most complete being 70 centimeters tall. This height spans for 10 vertebrae. The tail is extremely stiff. The furcula is U-V-shaped, which is seen in a wide variety of dinosaurs, most unrelated. Victoria Arbour et al. (2015) find said furcula to actually be chimeric, belonging to a turtle. In 2016, Depalma et al. recognized this, and extracted it from the dataset. It was flightless, with the humerus, radius, ulna, 2 metacarpal and partial fingers recovered. The humerus is relatively elongate and slander, being somewhat bent inwards. Quill knobs are present, which indicate the existence of wing feathers, despite flightlessness. This makes Dakotaraptor the largest dromaeosaur with confirmed feathering these knobs have a diameter of 8-10 millimeters, being large. Dakotaraptor may have had 15 of these. The ulna is 36 centimeters long and the radius is 32. Little mobility was present in the joints. Wingspan estimates do not take into account that the primary remiges may have exceeded the hand in length. The second metacarpal of the hand metacarpal bears a flat bony shelf at the dorsal that the primaries may lay across in life.

The hindlimb is lightly built contrary to most large dromaeosaurs. This matches the swift and agile-adapted legs of smaller dromaeosaurs. The thighbone is 558 millimeters long, being relatively shorter and lighter than *Utahraptor*. The shin is elongate and 678 millimeters long, 22% longer than the thighbone, which indicates capability for running. The cnemial crest bears a sharp corner that projects to the front. The fibulae crest ends in a hook that points above like in all theropods. The astragalus and calcaneum are fused, like *Bambiraptor*, with the top of the calcaneum having a small contact facet for the calf bone, which indicates the fibula had a narrow lower end. The metatatsus is about 32 centimeters long, which is relatively long. The sickle claws have a diameter of 16 centimeters and a length of 24 centimeters along the outer curve, being large and robust. This is 29% of the thighbone and 23% of the sickles in *Deinonychus*. It is flattened and the cross section forms a droplet shape. The flexor tubercle is larger compared to claw size than any dromaeosaur, which may give it the greatest slashing strength of all. The flexor tubercle of the third foot claw is almost non-existent. This suggests this claw had a minimized use since it is the most reduced of any dromaeosaur. The third claw is keeled, having a tip joint length of 7 centimeters and a curve length of 9 centimeters. The groove on the outer side nearer to the tip ends in a bone tunnel, which is a rare condition.

From a Facebook geology newsletter in 2014, supposed ichnofossil paleontologist Darin Kamins claims to have found Dakotaraptor material in their possession, including a rib and more of the skeleton from a new locality. However, this user has also claimed the Dakotaraptor holotype is not a chimera and that "they don't know what they're talking about". Currently, they have stated they are attempting to restore the "new material" and might publish research on the topic. Below is every available image of this supposed new rib:

## Classification

Dakotaraptor was first recovered as a dromaeosaurid, being sister to *Dromaeosaurus*. Then, it was was found to be in clade with *Utahraptor* and *Achillobator*. It was suggested to separate, being a 4th instance of size increase in dromaeosaurs:

Hartman et al. (2019) recover Dakotaraptor as a unenlagiid, which would mark one of the northernmost occurrences if true, disregarding the Hell Creek unenlagiid:

Currie and Evans (2019) recovered a eudromaeosaur, noting that the holotype may not be a single individual:

The naming of *Dineobellator* found the same as above, but noted its chimeric status, and casted doubt upon this placement, finding it to be too basal.

## Paleobiology

The sickle claw was used to pin down prey, of which it had a greater capability due to a stronger flexor tubercle. The third foot claw was smaller and seems to have had no function. Robust and gracile morphs are present, with both represented by adult specimens. Individual variation or pathologies may have induced this, but sexual dimorphism is the strongest explanation. It is unknown which morph represents what sex. Large pennaceous feathers were present despite being flightless. Instead, they may have shielded eggs, displayed, intimidated or kept balance during prey restraint. It may have descended from an ancestor that had these, and none of these functions do not necessitate wing feathers.

## Paleoecology

*Dakotaraptor* lived in the Hell Creek Formation, which was populated by a wide variety of fauna; mosasaurs, hadrosaurs, ceratopsians, dromaeosaurs, tyrannosaurs, oviraptorosaurs, ornithomimosaurs, alvarezsaurs, fish, pterosaurs, small ornithischians, mammals, insects, birds, crocodilians, turtles and others. It lived up until the K-PG boundary. It may have been a pack hunter, in which case it was capable of taking larger prey. It may have been a pursuit predator.

## References

1. ↑ https://www.researchgate.net/publication/308979112\_The\_furculae\_of\_the\_dromaeosaurid\_dinosaur\_Dakotaraptor\_steini\_are\_trionychid\_turtle\_entoplastra
2. ↑ https://peerj.com/preprints/1570/
3. ↑ 3.0 3.1 https://twitter.com/LancianIdolatry/status/1392150985288544258
4. ↑ 4.0 4.1 4.2 4.3 4.4 https://en.wikipedia.org/wiki/Dakotaraptor
5. ↑ https://twitter.com/saulilustrador/status/1484583093331767304
6. ↑ Darin Kamins on Facebook
7. ↑ https://en.wikipedia.org/wiki/Paleobiota\_of\_the\_Hell\_Creek\_Formation