Utahraptor (meaning "Utah's predator") is a genus of large dromaeosaurid (a group of feathered carnivorous theropods) dinosaur that lived during the Early Cretaceous period from around 139 to 135 million years ago in what is now the United States. The genus was described in 1993 by American paleontologist James Kirkland and colleagues with the type species Utahraptor ostrommaysi, based on fossils that had been unearthed earlier from the Cedar Mountain Formation of Utah. Later, many additional specimens were described including those from the skull and postcranium in addition to those of younger individuals. It is the largest-known member of the family Dromaeosauridae, measuring about 6–7 meters (20–23 ft) long and typically weighing around 500 kilograms (1,100 lb). As a heavily built, ground-dwelling, bipedal carnivore, its large size and variety of unique features have earned it attention in both pop culture and the scientific community. The jaws of Utahraptor were lined with small, serrated teeth that were used in conjunction with a large "killing claw" on its second toe to dispatch its prey. Its skull was boxy and elongated, akin to other dromaeosaurids like Dromaeosaurus and Velociraptor. Being a carnivore, Utahraptor was adapted to hunt the other animals of the Cedar Mountain Formation ecosystem such as ankylosaurs and iguanodonts. Evidence from the leg physiology supports the idea of Utahraptor being an ambush predator, in contrast to other dromaeosaurs that were pursuit predators. Fossil remains of several individuals of various ages have been found together, suggesting that Utahraptor was gregarious (social) and practiced degrees of post nestling care.
Discovery and naming
The first specimens of Utahraptor were found in 1975 by Jim Jensen in the Dalton Wells Quarry of Utah, near the town of Moab, but did not receive much attention. After the find of a large claw by Carl Limone in October 1991, James Kirkland, Robert Gaston and Donald Burge uncovered further remains of Utahraptor in 1991 in the Gaston Quarry in Grand County, Utah, within the Yellow Cat and Poison Strip members of the Cedar Mountain Formation. The holotype of Utahraptor, CEUM 184v.86, consists of a second pedal ungual, with potentially assigned elements from other specimens: pedal ungual CEUM 184v.294, tibia CEUM 184v.260 and premaxilla CEUM 184v.400. The holotype is housed in the paleontology collections of the Prehistoric Museum at Utah State University Eastern. Brigham Young University, the depository of Jensen's finds, currently houses the largest collection of Utahraptor fossils. The type species, Utahraptor ostrommaysi, was named by Kirkland, Gaston and Burge in June 1993. The genus name Utahraptor is in reference to Utah, where the remains were found. The specific name, ostrommaysi, is in honor to John Ostrom for his investigations on Deinonychus and its relationships to birds, as well as Chris Mays, who helped in the research of Utahraptor by founding Dinamation. From his description, Kirkland stated the meaning of genus name to be "Utah's predator," but the Latin word raptor translates to 'robber' or 'plunderer', not 'predator'. Earlier, it had been intended to name the species "U. spielbergi" after film director Steven Spielberg. It was alleged that this was in exchange for Spielberg funding paleontological research, and that the name was changed because agreement couldn’t be reached on the amount of financial assistance. Kirkland, however, later expressed that this was a misquote. He had changed the name to U. ostrommaysi shortly before the publication of the paper, as Universal Studios has begun threatening to sue museums that have exhibits with the word "Jurassic" in their titles; Dinamation, Kirkland's employers with connections to various museums, thus implored him to change the name, which he did.
In 2000, the specific name was emended by George Olshevsky to the plural genitive ostrommaysorum. However, Thiago Vernaschi V. Costa and Normand David in 2019 criticized the use of the species name U. ostrommaysorum, since it has no clear justification or explanation. Although this spelling has been largely used by other authors, the genus Utahraptor was originally coined with the type species U. ostrommaysi and, given that the International Code of Zoological Nomenclature offers no provision for forming a genitive form for persons with different names, Costa and David conclude that the original spelling ostrommaysi has to be regarded as an arbitrary combination of letters and not a correctly formed genitive form. Under this reasoning, ostrommaysorum has no valid use and the original spelling ostrommaysi does not need to be emended. Other alternative and also invalid spellings were used in scientific literature, such as ostromaysi, ostromaysorum, ostromayssorum, ostromayorum and ostrommaysori. Some elements were wrongly referred to the genus. The lacrimal bone of the specimen CEUM 184v.83 turned out to be a postorbital from the ankylosaur Gastonia. Britt and colleagues also suggested that the previously identified manual unguals of the specimens M184v.294, BYU 9438 and BYU 13068 are indeed pedal unguals. This suggestion was confirmed by Senter in 2007.
Description Utahraptor was one of the largest dromaeosaurids, with the largest elements assigned to the genus being slightly larger than the same bones in Achillobator. It was fairly robust compared to other dromaeosaurs, with stocky limbs proportioned more like those of other large theropods than those of its close relatives. Unlike its cousins, U. ostrommaysi had a robust lower jaw with a downturned tip, and as a result, the teeth at the front were quite procumbent. The characteristic "killing claw" of dromaeosaurids may, in U. ostrommaysi, have measured about 24 cm (9.4 in) in length, and its feet appear to have had a very tight grip. Based on evidence of filamentation in other dromaeosaurs, U. ostrommaysi was likely feathered.
Size
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