Etymology. Orr-Korr (‘‘Toothed River’’), name applied by Aoniken
Patagonian native people to the La Leona River, which runs not far from
the fossil site; and raptor, ‘‘thief’’ in Latin.
Orkoraptor burkei Novas, Ezcurra, and Lecuona, 2008
Etymology. Burkei, in honour to Coleman Burke, an American amateur geologist and paleontologist, who loves Patagonia and kindly supported our explorations in Argentina.
Locality and horizon. Los Hornos Hill, southern coast of Viedma Lake, SW Santa Cruz Province, Argentina. Pari Aike Formation, Upper Cretaceous (early Maastrichtian).
Holotype. MPM-Pv 3457, the specimen is represented by a right postorbital, a right quadratojugal, probable coronoid of the right side, eight isolated teeth, atlantal intercentrum and its right neurapophysis, two proximal caudal vertebrae, proximal half of right tibia, eight fragmentary ribs, and three incomplete chevrons. All of these bones were excavated froma single spot of 1.5 meters in diameter, in February of 2001.
Recovered skull dermal bones of Orkoraptor burkei.A, B, C, right postorbital; D, E, right quadratojugal; F, G, right coronoid?. (A, D, F) lateral, (B, E, G) medial, and (C) proximal views. Abbreviations: ap, ascending process; fc, frontal contact; jc, jugal contact; lc, laterosphenoid contact; qc, quadrate contact; rp, rostral process.
Referred specimens. MPM-Pv 3458, three well-preserved shed teeth, collected from the same beds as the holotype.
Teeth of Orkoraptor burkei (AeI). In A, B, and I the lineal drawing indicate cross-section profile. (G) mesial view. Abbreviations: cf, caudal furrow; cw, crown; md, median depression; rf, rostral furrow; wf, wear facet.
Diagnosis. Orkoraptor burkei is a large theropod differing from other tetanurans in the following combination of characters: teeth with unserrated and transversely wide mesial margins; teeth with a median depression flanked by two longitudinal and narrow furrows on the lingual surface (autapomorphy); postorbital with a wide jugal process, and an orbital margin that is obtuse and devoid of a suborbital flange; quadratojugal with a short jugal process; proximal caudal vertebrae with small pleurocoels (convergently aquired with Megaraptor, Carcharodontosauridae, and Oviraptorosauria).
Description. Orkoraptor burkei is a large theropod, approximately measuring 6-7 meters long, based on extrapolations with other large theropods, such as Albertosaurus and Sinraptor. Unequivocally, Orkoraptor is not a member of Abelisauroidea, Carcharodontosauridae, Alvarezsauridae, and Deinonychosauria, theropod clades that were frequently recorded in Cretaceous beds of South America. Otherwise, available evidence supports that Orkoraptor is a representative of a yet unknown branch of large tetanurans that inhabited South America at the close of the Cretaceous. The discovery of Orkoraptor lends support to the interpretation that tetanurans theropods were more diverse and abundant in South America than expected. The new Patagonian taxon, together with previously recorded evidence, demonstrates that by Maastrichtian times South America was populated by large theropods belonging to different lineages, including abelisaurids, a yet unnamed Deinonychosauria (Novas et al., 2004a), the derived maniraptoran Unquillosaurus (Novas and Agnolı´n, 2004), and the presently described Orkoraptor. References: Novas, F. E., Ezcurra, M. D., and Lecuona, A., 2008, Orkoraptor burkei nov. gen. et sp., a large theropod from the Maastrichtian Pari Aike Formation, Southern Patagonia, Argentina: Cretaceous Research, v. 29, p. 468-480.