Harrison Duran, a biology student at the University of California, Merced, had just been rejected from a summer internship when he received an invitation from a professor to go fossil hunting in a remote area of North Dakota.

Mr. Duran, 23, accepted the offer. Just four days into the two-week trip, he was helping uncover parts of a skull belonging to a triceratops, most likely about 65 million years old.

In an interview on Friday, Mr. Duran sounded a note of regret that he did not land the internship, at the La Brea Tar Pits and Museum in Los Angeles. Still, he said, he was happy with how things ultimately worked out.

“I think I found a more significant treasure in the Badlands,” he said.

On June 4, the pair spied what they first thought was petrified wood but later turned out to be a bone fragment — specifically, a roughly three - foot horn that would have been attached to the dinosaur’s left brow. The discovery was made in the Hell Creek Formation, a series of rock formations that cover parts of Montana and the Dakotas dating to the end of the Cretaceous Period about 66 million years ago .