Utahraptor is a medium sized Theropoddinosaur and is the largest dromaeosaurid. However it is also a relatively early Dromaeosaurid meaing that they might have evolved their small size later. Utahraptor is known from fossils that have been found in southwestern North America, hence its name meaning "Utah's predator".
Like all dromaeosaurids, Utahraptor was a lightly-built, gracile theropod. Contrary to popular belief, Utahraptor was likely not a fast-moving theropod. The dinosaur's femur is rather longer than its tibia, which suggests it would not have been able to run at great speed. Its body would have been slim and elegant in design. Despite being lightly built, Utahraptor was heavily armed: each of its feet bore a claw up to 24 cm in length, and its arms would have been long and powerful. Based on reconstructions of other dromaeosaurs, Utahraptor would have a coat of feathers rather than scales.
The Holotype specimen of Utahraptor is estimated to have measured around 5-7 meters long (16-23 feet), stand 2m tall at the hips, but weigh less than 500kg. This would make it an extremely lightly built theropod. There is, however, a possible second specimen of Utahraptor, certain bones of this specimen are twice the size of the holotypes, and so the animal in life would measure 14m long and has been estimated to have weighed at least 2.7t. This could theoretically put it in the size range of more famous large Carnivores such as Giganotosaurus and Tyrannosaurus. However, even if the 14m long Utahraptor is confirmed, it will still be smaller than some giant theropods like Carcharodontosaurus and especially Spinosaurus.
At first, dromaeosaurids were considered to be sluggish, lizard-like creatures, just like all Dinosaurs. However, in the 1950's, a large dromaeosaurid (large for a dromaeosaurid)known as Deinonychus was discovered, with evidence of an active lifestyle. Ever since Deinonychus was properly studied in the late 1950's, Dromaeosaurids have been thought of as fast, intelligent and pack hunting killing machines. Jurassic Park 3 greatly played upon this. Utahraptor, with its huge size, was said to be capable of killing any animal of its time. However, the Tibia (lower leg bone) was shorter than its Femur (upper leg bone) meaning it was not particulary fast. Also its sickle claw was not suited to the slicing of prey, it was probally more of a climing tool that along with the long arms, alowed Utahraptor to leap onto a prey item and make its way to the animals neck. Velociraptor, a smaller relative of Utahraptor, has been found locked in combat with a Protoceratops. The Velociraptor had its toe claw in the Protocertops neck. It is possible that Dromaeosaurids in general used their claw to stab the necks of their prey, they were probally agile enough to do this. If this is the case, Utahraptor's 24 cm toe claw would have been a formidible weapon to hunt.