| Oohkotokia | |
|---|---|
 | |
| Skull of the holotype, MOR 433 | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | †Ornithischia |
| Clade: | †Thyreophora |
| Clade: | †Ankylosauria |
| Family: | †Ankylosauridae |
| Subfamily: | †Ankylosaurinae |
| Tribe: | †Ankylosaurini |
| Genus: | †Oohkotokia Penkalski,2013 |
| Type species | |
| †Oohkotokia horneri Penkalski, 2013 | |
Oohkotokia (/ˌoʊ.oʊkəˈtoʊkiə/OH-oh-kə-TOH-kee-ə)[citation needed] is agenus ofankylosauriddinosaur within the subfamilyAnkylosaurinae. It is known from the upper levels of theTwo Medicine Formation (lateCampanian stage, about 74 Ma ago) ofMontana, United States. The discovery ofOohkotokia supports thatAnkylosaurine dinosaurs existed and flourished continuously in Montana and/or Alberta throughout the late Campanian and earlyMaastrichtian stages in theLate Cretaceous period. It was a large, heavily built,quadrupedal,herbivore, that could grow up to 5 metres (16 ft) long and weigh up to 2 metric tons (2.2 short tons).
The generic name,Oohkotokia, is derived from theBlackfoot 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 extensivebody armor. The generic name also honors the Blackfoot people, on whose land the specimen was found. The specific name,O. horneri, refers toJohn R. Horner of theMuseum of the Rockies, who collected the type specimen.[1]Oohkotokia contains a single typespecies,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.
Theholotype ofOohkotokia, MOR 433 consists of a crushed but rather well preserved skull that measured 375 mm, axial material, a partialscapula, several thin-walledosteoderms, cervical armour, a very large humerus, and other fragments. Estimates suggest thatOohkotokia was at best 5 metres (16 ft) long and weighed 2 metric tons (2.2 short tons) at most.[2] The skull of this genus bears great similarity to skulls that have been referred toEuoplocephalus, but is significant because it has a relatively smooth overall surface texture when compared to the skulls of most otherankylosaurids from the same time period.
Source:[1]
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 tailclub separates ankylosaurids likeOohkotokia from its close relatives thenodosaurids, 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.
Penkalski (2013) assigned this genus toAnkylosaurinae based on anatomical features present in the skull and the morphology of itsbody armor. There was sufficient morphological detail to conclude thatOohkotokia is a different animal than its relatives,Euoplocephalus tutus,Dyoplosaurus acutosquameus, andScolosaurus cutleri.[1]
Arbour and Currie (2013)[4] found thatOohkotokia shares diagnostic features withScolosaurus, including cervical half ring morphology and squamosal horn shape. They also noted that therostrum is broken in all specimens referred toOohkotokia (with some being reconstructed) and therefore the nasal plate morphology does not provide strong evidence for the separation ofOohkotokia. They concluded thatOohkotokia is ajunior synonym ofScolosaurus.
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. Anautapomorphy 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:[1]
The remains ofOohkotokia, MOR 433 were recovered in the Upper Member of theTwo Medicine Formation, inMontana, which radiometric dating has shown to be approximately 74 million years old.[5] The remains were collected in 1986–1987 in grey siltstone that was deposited during theCampanian stage of theCretaceous period.[1] The specimen is housed in the collection of theMuseum of the Rockies inBozeman, Montana.
Studies suggest that thepaleoenvironment of the Two Medicine Formation featured a seasonal, semi-arid climate with possiblerainshadows from the Cordilleran highlands. Lithologies, invertebrate faunas, and plant and pollen data suggest that during theCampanian, 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 ofoviraptorosaurs,ornithopods, thenodosaurEdmontonia, theceratopsiansAchelousaurus,Brachyceratops,Cerasinops, andEiniosaurus among others,Troodon, thedromaeosauridsBambiraptor,Dromaeosaurus andSaurornitholestes, and thetyrannosauroidsAlbertosaurus,Daspletosaurus andGorgosaurus. These dinosaurs andOohkotokia shared the same ancientpaleoenvironment with freshwaterbivalves,gastropods,turtles,lizards, andchampsosaurs. 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 includedhadrosaur nests with eggs and hatchlings, andTroodon eggs with intact embryos.[6][7][8][9]
The skull ofOohkotokia, 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. Thepremaxillary beak is missing and most of the palate has eroded away.[1] 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 themaxillae 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.[1]
