Clade †Megaraptora Phylum Chordata | Class Reptilia Species †O. burkei Rank Genus | |
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Similar Aerosteon, Megaraptora, Murusraptor, Neovenatoridae, Chilantaisaurus | ||
Orkoraptor is a genus of large theropod dinosaur from the late Cretaceous Period of Argentina. It is known from incomplete fossil remains including parts of the skull, teeth, tail vertebrae, and a partial tibia. The specialized teeth resemble those of some maniraptoriform theropods, namely the deinonychosaurs and compsognathids. This and other anatomical features led the authors who described it (Novas, Ezcurra, and Lecuona) to suggest that it was a maniraptoran Coelurosaur. However, subsequent studies found it to be a megaraptoran. Found in the Pari Aike Formation of Southern Patagonia, it is one of the southernmost carnivorous dinosaurs known from South America.
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Etymology
The name Orkoraptor means "Toothed River thief", and was derived from the Aoniken "Orr-Korr", the local name for the La Leona River, located near the original fossil site. The species name honors Coleman Burke, an amateur paleontologist who supported the expedition that collected the original fossils.
Description
Orkoraptor was a medium-sized theropod. In 2010, Gregory S. Paul estimated its length as 6 m (20 ft) and mass as 500 kilograms.
Classification
Orkoraptor was originally classified as Maniraptora incertae sedis. While the majority of phylogenetic trees recovered in its describers' analysis recovered it as a compsognathid, the describers considered this unlikely based on its much larger size and presence in much younger strata. Orkoraptor was subsequently recovered in Megaraptora, a clade including several other enigmatic medium to large theropods, which has variously been considered to be a member of Allosauroidea and Tyrannosauroidea. The phylogenetic trees in the publication of Gualicho shinyae have found megaraptorans to be either allosauroids or basal coelurosaurs.
Provenance
All known specimens of Orkoraptor were collected from the Pari Aike Formation, which is now considered by different authors to be either the middle section of the Mata Amarilla Formation, or merely an alternative name for the Cerro Fortaleza Formation. It was originally identified as coming from the Maastrichtian, and thus the youngest known megaraptoran, but more recently is considered to be from the Cenomanian to Santonian. The middle section of the Mata Amarilla Formation, whence Orkoraptor was collected, contains a tuff layer that has been dated to 96.2 ± 0.7 Ma, during the Cenomanian.
