Utahraptor ostrommaysi was a very large dromaeosaurid, or “raptor,” from the Early Cretaceous of what is now eastern Utah. It lived during part of the Early Cretaceous, probably in the first half of the period, although its exact age in millions of years is not precisely known. Its fossils come from the Cedar Mountain Formation in Grand County, Utah, where the rocks record river channels, floodplains, and wooded habitats.

This species was one of the largest known raptors, larger than Velociraptor and most of its close relatives. Adults are estimated to have reached roughly 5 to 7 meters in length, with body mass probably in the hundreds of kilograms, but exact weight is uncertain because the skeleton is incomplete and different studies give different numbers. The animal appears heavily built and muscular compared with many other dromaeosaurids, which suggests strong limbs and a powerful body rather than a lightly built runner.

Like other dromaeosaurids, Utahraptor had a large curved claw on the second toe of each foot. In big individuals, this claw could exceed about 20 centimeters in length and was strongly curved, which fits a role in gripping or controlling prey rather than simple walking. Its jaws carried sharp, serrated teeth well suited to cutting flesh.

No discovered Utahraptor fossils preserve feathers, but many closely related dromaeosaurids from other places and times do have clear feather impressions. For that reason, most paleontologists consider it very likely that Utahraptor also had feathers on at least parts of its body, even though this cannot yet be directly confirmed. Given its large size, any feathers it had would almost certainly not have been used for flight and were probably more important for insulation or visual display, although this remains an inference.

The Early Cretaceous environment of the Cedar Mountain Formation supported various plant-eating dinosaurs, small vertebrates, and other predators, so Utahraptor probably preyed on medium to large herbivores in this ecosystem. It may have used cover provided by vegetation and uneven terrain to approach prey at close range, but its exact hunting style is not directly known from fossils and ideas about ambush behavior remain hypotheses.

A single nine-ton block of rock from a site nicknamed “Utahraptor Ridge” preserves thousands of bones from baby to adult Utahraptor, along with bones from plant-eating dinosaurs.