The newly found tyrannosaur weighed about 2.5 tonnes and was 8 metres long (Source: Andrey Atuchin)
The meat-eating Lythronax argestes, which means "king of gore," had wide-set eyes that helped it track prey and a load of teeth packed into a more slender snout than T. rex, researchers write in the journal PLOS ONE.
The Lythronax was among the lighter, more compactly built tyrannosaurids, and may have been about half as heavy as the largest T. rex.
The beast weighed about 2.5 tonnes and was 8 metres long, says the research team led by Mark Loewen, adjunct assistant professor in the Department of Geology and Geophysics at the University of Utah.
Its bones - including parts of the skull, hips, leg and tail - were found in the Wahweap Formation within the Grand Staircase-Escalante National Monument in south-central Utah.
"The width of the back of the skull of Lythronax allowed it to see with an overlapping field of view - giving it the binocular vision - very useful for a predator and a condition we associate with T. rex," says Loewen.
It was also older - T. rex roamed the Earth about 10 to 12 million years later, researchers say.
Tyrannosaurids ran upright on two legs and had short arms, and attacked other dinosaurs as well as scavenging the carcasses of dead animals for food.
Researchers say they likely originated in northern Laramidia, then a swampy and humid island which is now western North America.
Several species likely moved south over time, while others made their way toward Asia 70 to 75 million years ago.