from the late Maastrichtian. O. sedens was named by Marsh in 1892 from partial remains found in the Lance Formation of Wyoming, only one year after the description of O. velox. Dale Russell, in his 1972 revision of ornithomimids, could not determine which genus it actually belonged to, though he speculated that it may be intermediate between Struthiomimus and Dromiceiomimus. In 1985 he considered it a species of Ornithomimus. Although it has since been referred to mainly as Struthiomimus sedens, based on complete specimens from Montana (as well as some fragments from Alberta and Saskatchewan), these yet have to be described and compared to the O. sedens holotype. The other is the original type species: O. velox, at first known from very limited remains. Additional specimens referred to O. velox have been described from the Denver Formation and from the Ferris Formation of Wyoming. One specimen attributed to O. velox (MNA P1 1762A) from the Kaiparowits Formation of Utah, was described in 1985. Re-evaluation of this specimen by Lindsay Zanno and colleagues in 2010, however, cast doubt on its assignment to O. velox, and possibly even to Ornithomimus. This conclusion was supported by a 2015 re-description of O. velox, which found that only the holotype specimen was confidently referable to that species. The authors of this study tentatively referred to the Kaiparowits specimen as Ornithomimus sp., along with all of the specimens from the Dinosaur Park Formation. Description Like other ornithomimids, species of Ornithomimus are characterized by feet with three weight-bearing toes, long slender arms, and long necks with birdlike, elongated, toothless, beaked skulls. They were bipedal and superficially resembled an ostrich. They would have been swift runners. They had very long limbs, hollow bones, and large brains and eyes. The brains of ornithomimids in general were large for non-avialan dinosaurs, but this may not necessarily be a sign of greater intelligence; some paleontologists think that the enlarged portions of the brain were dedicated to kinesthetic coordination. The bones of the hands are remarkably sloth-like in appearance, which led Henry Fairfield Osborn to suggest that they were used to hook branches during feeding. Ornithomimus differ from other ornithomimids, such as Struthiomimus, in having shorter torsos, long slender forearms, very slender, straight hand and foot claws and in having hand bones (metacarpals) and fingers of similar lengths. The two Ornithomimus species today seen as possibly valid differ in size. In 2010