Orkoraptor

*Orkoraptor burkei*

***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.

## 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. Paulestimated its length as 6 m (20 ft) and mass as 500 kilograms. In 2016, Molina-Pérez and Larramendi gave a higher estimate of 8.4 meters and 1.4 tons for the holotype specimen. The holotype, MPM-Pv 3457 , was excavated in 2001 and consists of a right postorbital, a right quadratojugal, a probable right coronoid, eight isolated teeth, the intercentrum of the atlas and its right neurophophysis, two proximal caudal vertebrae, the proximal half of the right tibia, eight fragmentary ribs and three incomplete chevrons. It was initially believed to be a coelurosaurian due to the upward anterior process of the postorbital, as well as the specialized teeth that are not serrated on the mesial, frontal side and have a figure- 8 -shaped cross section , similar to dromaeosaurids and compsognathids. However, many other characteristics contradict those of these families and other coelurosaurians, so its original describers could not conclusively assign it to any specific family. They noted its similarity to a then-undescribed Patagonian theropod now known as Murusraptor . More recent analyzes have explained that these coelurosaur-like traits are also present in some megaraptorans. For example, the postorbital of Orkoraptor is almost identical to that of Aerosteon and the juvenile Megaraptor described in 2014 has teeth similar to those of Orkoraptor.

## 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.

## Appearance in other media

### *Jurassic Park*

* Orkoraptor appeared in the Jurassic World toys.