Researchers on Friday announced the discovery of a killer dinosaur that roamed North America in what is now Utah about 100 million years ago.



Experts from the Field Museum in Chicago and the North Carolina Museum of Natural Sciences in Raleigh, N.C., -- reporting in the journal Nature Communications -- said the two-legged reptile predates the Tyrannosaurus rex.



"This dinosaur was a colossal predator second only to the great T. rex and perhaps Acrocanthosarus in the North American fossil record," said Lindsay Zanno, the lead author on the paper and the Director of Paleontology at NCMNS.



Officials have named the beast "Siats meekerorum," after a legend of Utah's Ute tribe and a family that has donated to the Field Museum. They said the dinosaur was more than 30 feet long and weighed more than four tons.



The new dinosaur is the first of its kind to be discovered in North America. Pieces were found five years ago as part of a Field Museum expedition to 100-million-year-old rocks of the Cedar Mountain Formation in Utah. The scattered remains of this animal were retrieved from a giant excavation over two summers, and then painstakingly cleaned from rock by staff and volunteers at The Field Museum.



"We were thrilled to discover the first dinosaur of its kind in North America and add to mounting evidence that dinosaurs were widely dispersed across the globe 100 million years ago" says study co-author and Curator of Dinosaurs at the Field Museum, Peter Makovicky.



Despite its large size, Siats is not a close relative of T. rex and other tyrannosaurs that were the dominant predators in North America for the last 20 million years of the age of dinosaurs. Rather, it belongs to the carchardontosaurian group of theropods -- predatory dinosaurs -- whose more famous members include giants like the Argentinean Giganotosaurus. Siats belongs to a branch of the carcharodontosaurian family tree that was previously unknown in North America.