Dakotaraptor

Dakotaraptor (meaning "thief from Dakota") is a possible chimaeric genus of maniraptoriform theropod dinosaur that lived in western North America during the Late Cretaceous period. The remains of this dinosaur were found in the Maastrichtian-aged Hell Creek Formation, which dates to the very end of the Mesozoic era. This makes Dakotaraptor one of the last surviving dromaeosaurids, although some scientists have questioned this classification.

One of the largest known dromaeosaurids, Dakotaraptor measured between 4.35 to 6 metres (14.3 to 19.7 feet) long and weighed between 220 to 350 kilograms (490 to 770 pounds). The fossils of D. steini were discovered in an area where many different kinds of animals were found together. However, some of the bones thought to belong to Dakotaraptor were later identified as coming from trionychid turtles. Because the main fossil specimen is kept in a private collection, it is difficult for scientists to study it further to confirm its exact classification.

Studies of D. steini have placed it in various positions within the group Dromaeosauridae, showing that scientists are still learning about where this dinosaur fits in the family tree of its relatives.

Discovery and naming

In 2005, paleontologist Robert DePalma found the first bones of this dinosaur in Harding County, South Dakota. These bones were part of a larger group of dinosaur remains found together. In 2015, the dinosaur was officially named Dakotaraptor steini by several scientists. The name combines "Dakota," referring to the area and the Dakota people, with "raptor," meaning "plunderer" in Latin. The species name "steini" honors paleontologist Walter W. Stein.

The main fossil, called the holotype, was discovered in a sandstone layer of the Hell Creek Formation, which dates to the very end of the time when dinosaurs lived. It includes parts of the dinosaur's body but not its skull, such as vertebrae, arm and leg bones, and claws. Later, more bones were found that might belong to Dakotaraptor, but some of these were later identified as coming from other animals, like turtles. Scientists are still studying these fossils to learn more about this dinosaur.

Description

Size

Dakotaraptor is very big for a dromaeosaurid, with an estimated adult length of 5.5 m (18 ft). Other guesses in 2016 said it could be between 4.35 m and 6 m (14.3–19.7 ft) long and weigh between 220 kg and 350 kg (490–770 lb).

This size is close to one of the largest known dromaeosaurids, Utahraptor. But Dakotaraptor looks more like smaller dromaeosaurids, such as Deinonychus, not like Utahraptor.

Distinguishing traits

Besides its large size, Dakotaraptor has some special features. The boss on the fourth foot claw that holds a tendon is smaller. The “blood groove” on the outer side of the fourth foot claw is closed over half its length, forming a bony tube. The second and third foot claws have sharp edges underneath. The second foot claw, called the “sickle claw,” is 29% the length of the thighbone. The shinbone has a long, thin crest that ends in a hook. On the hand bone, the inner condyle is almost as big as the outer one. The teeth have many small points along their edges.

Skeleton

Vertebral column

The back bones of Dakotaraptor are filled with air spaces. On the middle tail bones, the front joints are very long, about 70 centimetres (28 in), and help stiffen the tail.

Arms

The wing of Dakotaraptor got a lot of attention when it was described. Here, “wing” means the arm with long feathers, like in birds, even though Dakotaraptor could not fly. Many arm bones were found, so the wing is well known. The upper arm bone is long and slightly bent. A special feature is a row of bumps on the lower arm bone, called quill knobs. These bumps show where wing feathers attached, proving that Dakotaraptor had large feathers. The lower arm bone is 36 centimetres (14 in) long, and the other bone is 32 centimetres (13 in) long. The hand joints didn’t move much. The wingspan was about 120 centimetres (47 in).

The second hand bone had a flat surface for the main feathers to rest on.

Legs

Dakotaraptor’s legs were light and long, unlike the heavy legs of Utahraptor. Dakotaraptor looked more like smaller, quick dromaeosaurids and was good at running. The thighbone is 558 millimetres (22.0 in) long. But the shinbone is longer, at 678 millimetres (26.7 in), the longest known dromaeosaurid tibia. The shinbone’s top edge has a sharp corner, and its side ends in a hook shape, which is unique among Theropoda. The ankle bones are fused and similar to those in Bambiraptor. The foot is long compared to the rest of the leg.

The foot claws include a big “sickle claw” used for catching or holding prey. It is 24 centimetres (9.4 in) long along the curve and has a strong base for powerful slashing. The third claw is much smaller and has a bone tunnel near the tip, which is rare.

Classification

Dakotaraptor was placed in Dromaeosauridae. Studies show it may be closely related to other dinosaurs like Dromaeosaurus, Utahraptor, and Achillobator. Some scientists think Dakotaraptor might be part of a different group called Unenlagiidae.

Recent studies suggest that Dakotaraptor might not be a single species but could be made up of pieces from different dinosaurs. As of 2024, scientists are still unsure exactly where Dakotaraptor fits in the family tree of dinosaurs.

Possible synonymy with Acheroraptor

Acheroraptor temertyorum is another dinosaur from the same time and place as Dakotaraptor. Acheroraptor was smaller and had ridges on its teeth, but scientists like Andrea Cau wonder if Acheroraptor might just be a smaller version of Dakotaraptor. However, analysis of the fossils did not show these two dinosaurs to be closely related.

Paleobiology

Dakotaraptor had a special claw on its second toe, called the "sickle claw," which it used to catch prey. This claw was stronger than the one found in another dinosaur called Utahraptor. The third claw on its foot was smaller and probably not used much for attacking.

Scientists noticed two different body types in the fossils—one stronger and one lighter. Both types were adults, so the difference wasn’t because one was younger. It might be because of natural differences or because of gender, but we don’t know for sure which was male and which was female.

Dakotaraptor had places on its lower arm where big feathers would have attached. Even though these dinosaurs were too heavy to fly, they still had these feathers. The feathers might have helped protect eggs, show off, scare others, or help keep balance while catching prey. Scientists think Dakotaraptor may have come from a smaller ancestor that could fly and kept these feathers for other uses.

Paleoecology

Dakotaraptor is a medium-sized dinosaur found in the Hell Creek Formation, discovered after Nanotyrannus. It was smaller than the giant Tyrannosaurus but bigger than smaller dinosaurs like Acheroraptor. Because its lower leg bone was longer than its upper leg bone, Dakotaraptor could run very fast. It may have hunted in groups and could have chased down larger plant-eating dinosaurs, sometimes competing with younger Tyrannosaurus that were about 6 to 9 metres long. Dakotaraptor lived at the same time as other famous Hell Creek dinosaurs such as Tyrannosaurus, Triceratops, Pachycephalosaurus, Ornithomimus, and Edmontosaurus.