Description and Classification

Dakotaraptor was a notably large member of the Dromaeosauridae family, often called “raptors.” Scientists estimate it reached lengths of about 5 to 6 meters (17 to 20 feet), making it similar in size to another large dromaeosaurid, Utahraptor, though Dakotaraptor had a more slender and agile build. This suggests it was a fast runner for its size. Like many other theropods in its group, such as Velociraptor, Dakotaraptor was likely covered in feathers. Strong evidence for this comes from quill knobs, which are small bumps on the ulna (a forearm bone) where large feathers would have attached. This indicates Dakotaraptor had well-developed feathers on its arms, possibly forming wing-like structures, though it was too large to fly.

As a dromaeosaurid, Dakotaraptor possessed the characteristic large, sickle-shaped “killing claw” on the second toe of each foot. This sharp claw, which measured about 24 centimeters (9.5 inches) along its outer curve, would have been a formidable weapon. Dakotaraptor is classified within the group Maniraptora, which includes birds and their closest dinosaur relatives. Its discovery showed that large dromaeosaurids were present in North America right up until the end of the Cretaceous period, sharing their environment with giant predators like Tyrannosaurus rex.

Distinguishing Features

Dakotaraptor had several features that help scientists identify it and understand its lifestyle:

• It was one of the largest known dromaeosaurids, comparable in length to Utahraptor but with a more lightweight and agile frame.
• The presence of distinct quill knobs on its ulna (forearm bone) provides direct evidence of large, pennaceous (wing-like) feathers on its arms.
• It possessed a very large, retractable sickle-shaped claw on the second toe of each foot, measuring about 24 cm (9.5 inches) along the curve, used for subduing prey.
• Its leg bones, particularly the tibia (shin bone), were relatively long, indicating it was a capable runner.
• Certain features of its ankle bones (astragalus and calcaneum) are unique among dromaeosaurids.
• Its vertebrae suggest it had a stiffened tail, typical for dromaeosaurids, which would have helped with balance while running and turning.

Paleoenvironment and Diet

Dakotaraptor lived in what is now the Hell Creek Formation of South Dakota and Montana during the latest Maastrichtian age of the Late Cretaceous period, approximately 66 million years ago. This was just before the asteroid impact that led to the extinction of the non-avian dinosaurs. The environment was a subtropical coastal plain with a warm, humid climate, crisscrossed by rivers and dotted with forests, open woodlands, and swamps. This rich ecosystem supported a diverse range of dinosaurs.

As a carnivore, Dakotaraptor would have been an active predator. Given its size and agility, it likely hunted medium-sized herbivorous dinosaurs, such as young hadrosaurs like Edmontosaurus, ornithomimids (ostrich-like dinosaurs), or pachycephalosaurs (dome-headed dinosaurs). It may have competed for food with juvenile Tyrannosaurus rex, which were of a similar size. The large sickle claws on its feet were likely used to pin down and kill its prey. It is unknown whether Dakotaraptor hunted alone or in packs, a behavior sometimes suggested for other dromaeosaurids.

Significance and Ongoing Research

The discovery of Dakotaraptor, announced in 2015, was significant because it revealed a new top-tier predator in the well-studied Hell Creek Formation. It demonstrated that very large dromaeosaurids existed alongside Tyrannosaurus rex at the very end of the age of dinosaurs. This helped fill an ecological niche for a medium-to-large-sized, agile predator, different from the massive T. rex or smaller raptors like Acheroraptor from the same environment. The clear evidence of large arm feathers on Dakotaraptor also reinforced the understanding that many theropod dinosaurs, even large ones, were feathered.

Ongoing research continues to refine our understanding of Dakotaraptor. There has been some scientific debate regarding some of the initial fossil material. For example, a bone initially thought to be its furcula (wishbone) was later identified as part of a turtle’s armor. However, this does not invalidate the genus itself, which is based on other distinct skeletal elements like limb bones that show clear dromaeosaurid characteristics and quill knobs. Paleontologists are still working to pinpoint its exact relationships to other dromaeosaurids like Utahraptor and Dromaeosaurus. Future fossil discoveries will be crucial for painting a more complete picture of Dakotaraptor‘s anatomy, behavior, and its role in the Late Cretaceous ecosystem.