A new study published Monday concluded that the famous Triceratops - named and known for their three prominent horns - took around two million years of evolution to arrive at their signature form.

According to the 15-year study conducted by the researchers at the Montana State University, the Triceratops did not always have the magnificent set of horns they are so well known for. The dinosaur once had a longer beak and shorter horns, which over the course of over a million years of evolution developed into a more deadly display.

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Year after year, researchers returned to the Hell Creek Formation in Montana where the largest specimen of Triceratops are found.

Scientists have long struggled to find the relationship between the triceratops prorsus, characterized by short beak and long nasal horn, and triceratops horridus whose main feature is a long beak and short nasal horn.

Previous researches theorized that the slight difference in the specimens' facial profiles determine between male and female Triceratops. Other groups of researchers believed that prorsus and horridus are two separate evolved forms of the three-horned dinosaur.

However, John Scanella and colleagues ascertained that "over one to two million years at the end of the Cretaceous Period, Triceratops went from having a small nasal horn and long beak to having a long nasal horn and shorter beak."

"This striking change in physical display suggests they evolved," Scanella explained, "though it's difficult to say what drove the change."

Based on their study of 50 triceratops skull specimens excavated in the badlands of Eastern Montana, the team also concluded that the dinosaur's horns and skull changed as individual creature aged.

Triceratops roamed the earth near the final stage of the Cretaceous period. They arrived at their popular form around half a million years before the dinosaurs went extinct.

Scanella's study came out with the June 30 issue of the journal "Proceedings of the National Academy of Sciences."

Tagstriceratops, three-horned dinosaur, Scanella, Hell Creek Formation, evolution