Triceratops found on a Denver-area construction site revealed to be a much rarer dinosaur

The seeming bones of a triceratops found at a Denver-area construction site turned out to be those of a much rarer dinosaur. 

The Denver Museum of Nature and Science said Tuesday that the skull and partial skeleton found in the suburb of Thornton last August belonged to a torosaurus, the triceratops' close cousin.

“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,"  Joe Sertich, the museum's dinosaur curator, said in a statement.

"The Thornton beast is by far the most complete, and best preserved, ever found.”

One giveaway that it wasn't a triceratops, the museum said: The bone "shield" of the skull points backward off the head. That feature, called the frill, is thinner and more delicate on the torosaurus.

Otherwise, the two dinos are virtually identical. Both have large horns over their eyes and a third, smaller horn on the nose.

The fossils surfaced on Aug. 28 at the construction site of a future police and fire station. An eagle-eyed engineer halted digging when a soil examination revealed something inconsistent with the area's sand and claystone, the Denver Post reported. 

A lower jaw beak, brow and shoulder bones and even a stray T. rex tooth showed up after careful excavations, per the Post. About 95% of the skull and 20% or more of the' skeleton are now identified, the museum said, making the torosaurus — nicknamed "Tiny" by local schoolchildren — the most complete Cretaceous Period fossil in state history. 

Follow Josh Hafner on Twitter: @joshhafner