SPRINGFIELD, Ill. – The vertebra of an extinct Harlan’s muskox from the Ice Age went on display Friday at the Illinois State Museum after a Springfield man made the rare discovery in the drought-shallowed Sangamon River.

Tony Blisset, a McDonald’s manager, said he was swimming with his family Wednesday when he jumped into chin-deep water and found the bone. At first, he said, he thought it was from a horse or cow. But then he contacted the museum, where paleontologists informed him of his significant find.

“It was hidden for a long time, just waiting to be found and discovered,” Blisset said.

The species of muskox lived in Illinois during the Ice Age and scientists say Blisset’s find is the thirteenth record of the species in Illinois.

“It’s an important discovery,” museum paleontologist Jeffrey Saunders said. “They were on the river on a 106-degree day during a near record, if not record, drought and what should they do is discover the fossil of an Ice Age animal?”

Officials say the Sangamon River was 11 feet lower in July than in May. Scientists think the bone eroded out of sediments during high water and was redeposited. Blisset has donated the vertebra to the museum.