Description and Classification

Oohkotokia was a member of the Ankylosauridae family, a group of plant-eating dinosaurs known for their extensive body armor. Like other ankylosaurids, Oohkotokia was a heavily built, four-legged dinosaur that walked low to the ground. It would have been covered in bony plates called osteoderms, which provided protection from predators. It also likely possessed a bony club at the end of its tail, a common feature in advanced ankylosaurids, used for defense.

The known fossil material of Oohkotokia includes parts of the skull, vertebrae, armor scutes, and portions of the limbs and tail club. Based on these remains, scientists estimate it was a medium-sized ankylosaur, though precise size estimates are difficult due to the incompleteness of the fossils. Its body would have been broad and tank-like. Oohkotokia is classified within the subfamily Ankylosaurinae, placing it among other well-known armored dinosaurs such as Ankylosaurus and Euoplocephalus.

Distinguishing Features

Oohkotokia is distinguished from other ankylosaurids based on a combination of features, particularly in its skull and armor. Some of these key characteristics include:

• A relatively large, low, and rounded squamosal horn (a horn-like projection at the back corner of the skull) that was ornamented with grooves.
• A prominent, triangular, and peaked caputegulum (a type of head armor plate) located on the nasal bones above the snout.
• The caputegulae (plural for caputegulum) on the top of its head, in the region covering the frontal and parietal bones, were polygonal (many-sided) and generally flat or only slightly domed.
• The cervical half-rings, which were shield-like structures of fused osteoderms protecting the neck, featured bony plates with distinct keels.

Paleoenvironment and Diet

Oohkotokia lived in the environment preserved in the Two Medicine Formation of Montana. During the Late Cretaceous, this area was a seasonal, semi-arid coastal plain with rivers, floodplains, and some forested areas. It was located further inland from the Western Interior Seaway, a large sea that once divided North America. This environment supported a diverse range of dinosaurs.

As an herbivore, Oohkotokia would have fed on low-growing plants such as ferns, cycads, and early flowering plants. Its broad snout and leaf-shaped teeth were suited for cropping vegetation. It shared its habitat with many other dinosaurs, including hadrosaurs like Maiasaura and Hypacrosaurus, ceratopsians such as Einiosaurus and Achelousaurus, and predators like the tyrannosaurid Daspletosaurus.

Significance and Ongoing Research

The discovery of Oohkotokia adds to our understanding of ankylosaur diversity in North America during the Late Cretaceous period. It suggests that there were multiple types of armored dinosaurs living in the same ecosystems. However, the validity of Oohkotokia as a distinct genus is a subject of ongoing scientific discussion and research.

Some paleontologists have suggested that the features used to define Oohkotokia might fall within the range of variation seen in other ankylosaur genera, such as Scolosaurus or Euoplocephalus. It is possible that the known Oohkotokia material could represent individuals of different ages or sexes of these other species, or simply individual variation. Further discoveries of more complete ankylosaur fossils from the Two Medicine Formation are needed to help clarify the relationships between these armored dinosaurs and to confirm the distinct status of Oohkotokia. This ongoing research highlights the complexities of identifying new dinosaur species from incomplete fossil evidence.