Utah raptor (meaning "Utah's predator" or "Utah's thief") is a genus of theropod dinosaurs. It contains a single species, Utahraptor ostrommaysorum, which is the largest-known member of the family Dromaeosauridae. Fossil specimens date to the upper Barremian stage of the early Cretaceous period (in rock strata dated to 126 ± 2.5 million years ago).
The holotype specimen of Utahraptor is fragmentary, consisting of skull fragments, a tibia, claws and some caudal (tail) vertebrae. These few elements suggest an animal about twice the length of Deinonychus. Like other dromaeosaurids, Utahraptor had large curved claws on their second toes. One claw specimen is preserved at 22 centimeters (8.7 in) in length and is thought to reach 24 cm (9.4 in) restored.
The largest described U. ostrommaysorum specimens are estimated to have reached up to 5.7 meters (19 ft) long and somewhat less than 500 kilograms (1,100 lb) in weight, comparable to a grizzly bear or polar bear in size. However, the 2001 Kirkland discovery indicates the species may be far heavier than previously estimated.
It is thought that Utahraptor is closely related to the smaller Dromaeosaurus and the giant Mongolian and North American dromaeosaurid genera Achillobator and Dakotaraptor, based on cladistic analysis.
Although feathers have never been found in association with Utahraptor specimens, there is strong phylogenetic evidence suggesting that all dromaeosaurids possessed them. This evidence comes from phylogenetic bracketing, which allows paleontologists to infer traits that exist in a clade based on the existence of that trait in a more basal form.