DENVER -- A nearly complete skull and partial skeleton of what was believed to be a triceratops discovered at a Thornton construction site in August has turned out to be something different -- and more rare.
The Denver Museum of Nature and Science said Tuesday the 66-million-year-old fossils are instead those of a torosaurus, a close cousin of triceratops.
The frill, or the "shield," of bone projecting backward from the head helped reidentify the fossils.
The triceratops and torosaurus had a large horn over each eye and a smaller nose horn.
Officials believed during excavation that the fossils were those to the more common triceratops.
But the torosaurus had a longer, thinner and more delicate frill with two large holes. The frill features were discovered after the skull was cleaned and compared to triceratops specimens at the museum.
“Not only is the fossil more complete and better preserved than I imagined, but it has also revealed itself to be something extremely rare,” said Joe Sertich, curator of dinosaurs at the museum.
“While the number of good triceratops specimens collected from the American West likely exceeds 2,000 individuals, there are only about seven partial skulls of torosaurus known. The Thornton beast is by far the most complete, and best preserved, ever found.”
Construction crews working working on Thornton’s new public safety facility at 132nd Avenue and Quebec Street uncovered the skull and skeleton on Aug. 25.
An estimated 95 percent of the skull and at least 20 percent of the skeleton have been identified. It's the most complete Cretaceous Period fossil discovered in Colorado, officials said.