A close relative of Velociraptor and measuring up to three meters in length, Deinonychus is a genus of theropod dinosaur that belongs to the dromaeosaur family. Its skull is shorter than that of Velociraptor, with large pronounced eye ridges. Its name means "Terrible Claw", a reference to the 8-inch long, retractable sickle claw on the second toe of its feet, which Deinonychus uses to defend itself from predators and attack its prey. It once hunted across North America around 120 million years ago during the Early Cretaceous period, and its discovery led to a dramatic change in how dinosaurs were perceived – that birds are descended from dinosaurs. Like Velociraptor, Deinonychus is a swift-moving predator as well as a pack hunter. Although Velociraptor had been discovered earlier, Deinonychus was the first raptor known from an almost complete skeleton.