Extinct genus of dinosaurs
Oohkotokia ( ) is a genus of ankylosaurid dinosaur within the subfamily Ankylosaurinae. It is known from the upper levels of the Two Medicine Formation (late Campanian stage, about 74 Ma ago) of Montana, United States. The discovery of "Oohkotokia" supports that Ankylosaurine dinosaurs existed and flourished continuously in Montana and/or Alberta throughout the late Campanian and early Maastrichtian stages in the Late Cretaceous period. It was a large, heavily built, quadrupedal, herbivore, that could grow up to long and weigh up to .
Discovery and naming.
The generic name, "Oohkotokia", is derived from the Blackfoot animate noun "ooh’kotoka", meaning "large stone" and the Latin suffix "ia" meaning "derived from"; thus "child of stone", which is a reference to its extensive body armor. The generic name also honors the Blackfoot people, on whose land the specimen was found. The specific name, "O. horneri", refers to John R. Horner of the Museum of the Rockies, who collected the type specimen. "Oohkotokia" contains a single type species, Oohkotokia horneri, named and described in 2013 by Paul Penkalski. Penkalski described this genus after finding it in the collection of Montana's Museum of the Rockies where it had been stored for more than three decades.
Description.
The holotype of "Oohkotokia", MOR 433 consists of a crushed but rather well preserved skull that measured 375 mm, axial material, a partial scapula, several thin-walled osteoderms, cervical armour, a very large humerus, and other fragments. Estimates suggest that "Oohkotokia" was at best long and weighed at most. The skull of this genus bears great similarity to skulls that have been referred to "Euoplocephalus", but is significant because it has a relatively smooth overall surface texture when compared to the skulls of most other ankylosaurids from the same time period.
Tail.
Like other ankylosaurids, "Oohkotokia" had an enlarged mass of bone forming a "club" on the end of its tail, made of two enlarged bone lumps. The presence of this type of tail club separates ankylosaurids like "Oohkotokia" from its close relatives the nodosaurids, who do not have this tail feature. Its tail club was made of several plates of bone, permeated by soft tissue, which allowed the absorption of thousands of pounds of force. The large clubs at the end of their tails may have been used in self-defense, by swinging the club at predators or rivals, or in sexual selection.
Classification.
Penkalski (2013) assigned this genus to Ankylosaurinae based on anatomical features present in the skull and the morphology of its body armor. There was sufficient morphological detail to conclude that "Oohkotokia" is a different animal than its relatives, "Euoplocephalus tutus", "Dyoplosaurus acutosquameus", and "Scolosaurus cutleri".
Arbour and Currie (2013) found that "Oohkotokia" shares diagnostic features with "Scolosaurus", including cervical half ring morphology and squamosal horn shape. They also noted that the rostrum is broken in all specimens referred to "Oohkotokia" (with some being reconstructed) and therefore the nasal plate morphology does not provide strong evidence for the separation of "Oohkotokia". They concluded that "Oohkotokia" is a junior synonym of "Scolosaurus".
Distinguishing anatomical features.
A diagnosis is a statement of the anatomical features of an organism (or group) that collectively distinguish it from all other organisms. Some, but not all, of the features in a diagnosis are also autapomorphies. An autapomorphy is a distinctive anatomical feature that is unique to a given organism or group.
According to Penkalski (2013), "Oohkotokia" can be distinguished based on the following characteristics:
Paleoecology.
Provenance and occurrence.
The remains of "Oohkotokia", MOR 433 were recovered in the Upper Member of the Two Medicine Formation, in Montana, which radiometric dating has shown to be approximately 74 million years old. The remains were collected in 1986–1987 in grey siltstone that was deposited during the Campanian stage of the Cretaceous period. The specimen is housed in the collection of the Museum of the Rockies in Bozeman, Montana.
Fauna and habitat.
Studies suggest that the paleoenvironment of the Two Medicine Formation featured a seasonal, semi-arid climate with possible rainshadows from the Cordilleran highlands. Lithologies, invertebrate faunas, and plant and pollen data suggest that during the Campanian, this region experienced a long dry season and warm temperatures. The extensive red beds and caliche horizons of the upper Two Medicine are evidence of at least seasonally arid conditions.
The Two Medicine Formation has produced the remains of oviraptorosaurs, ornithopods, the nodosaur "Edmontonia", the ceratopsians "Achelousaurus", "Brachyceratops", "Cerasinops", and "Einiosaurus" among others, "Troodon", the dromaeosaurids "Bambiraptor", "Dromaeosaurus" and "Saurornitholestes", and the tyrannosauroids "Albertosaurus", "Daspletosaurus" and "Gorgosaurus". These dinosaurs and "Oohkotokia" shared the same ancient paleoenvironment with freshwater bivalves, gastropods, turtles, lizards, and champsosaurs. Some of the dinosaurs from this formation have been speculated to have shown signs of drought related death. The Upper Two Medicine Formation is particular significant for discoveries of a range of ontogenetic stages in dinosaurs, which has included hadrosaur nests with eggs and hatchlings, and "Troodon" eggs with intact embryos.
Taphonomy.
The skull of "Oohkotokia", specimen MOR 433 is crushed but is overall reasonably well preserved on its dorsal and lateral surfaces, but its midline is offset to the animal's left side. The premaxillary beak is missing and most of the palate has eroded away. The crushing suggests that it was the result of dinoturbation, which is the trampling of soils, sediments and bones by passing dinosaurs. A roughly triangular area is present around which the bones of the skull have been splayed outward, as if the skull was stepped on prior to fossilization. The alveolar borders of the maxillae were eroded and no teeth were preserved. The recovered fossil material ranges from red to grey, but the coloration is not thought to bear any taphonomic significance, and the variation most likely arose from differential weathering.
References.
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