The raptor was among several discovered at or near Doelling's Bowl Bone Bed, about 230-miles southeast of Salt Lake City, which has yielded several new species in the last two decades and is thought to be the base of Utah's Cretaceous record. Fossils found at the bone bed are estimated at between 120 and 130 million years old.
The new creature, a predator, has been designated as a new dinosaur genus and species known as Yurgovuchia doellingi, said Jim Kirkland, state palaeontologist for Utah's Geological Survey.
A description of the dinosaur has been published this week in the journal PLoS One.
Yurgovuchia is the first new species unearthed in Doelling's Bowl to be named, although Kirkland said scientists believe as many as six new species may have been found at the site he described as "richer than any other place in the US"
"All we are finding are new species," he said. "I think there are places where what we are seeing (is) evolving populations."
The new raptor is believed to be an ancestral relative of the younger and much larger Utahraptor, based on similarities in pieces of fossilised vertebrae recovered. In both species, the bundles of rods that jut out from the vertebrae to form the raptor's tail are shortened, said Kirkland.
The new dinosaur's name was based on the Ute Indian word for coyote, 'yurgovuch', and for the location where it was found, itself named after Utah palaeontologist Helmut Doelling, whose geological mapping of the Arches region led to the bone bed's discovery.
Raptors, or dromaeosaurs, are a diverse family of predatory dinosaurs known for their stiff tails and a large, recurved claw that protruded from the second toe of their hind feet.
Raptors ranged in size from as small as a mockingbird to as big as a bear, Kirkland said. Some were covered in feathers, although scientists don't believe they could fly.
Utah palaeontologists first came across the Yurgovuchia specimen in 2005 and excavation began the next year, over time recovering sections of the vertebrae and a portion of a pelvis.
Two other sets of bones that also appear to be from new species were recovered.
One set was found within a metre of the Yurgovuchia at Doelling's Bowl. The third was a broken, but distinctive skeleton of a long tail, found at a nearby site, says Kirkland.
Both need more study and the Utah Geological Survey plans additional excavation work. Palaeontologists were also working on the excavation of bones from a long-necked dinosaur that may represent yet another previously unknown species, he said.
"It's real exciting," said Kirkland.