A teenager looking for minnows in the Cedar River near Cedar Rapids stumbled upon a bison skull. University of Iowa professor emeritus, Holmes Semken, talked with 16-year-old Cody Sprague who found the skull.

Semken says Sprague knew right away it was something different. “Found it in a sand and gravel deposit, which suggests it was redeposited in the river. Probably in the 2008 flood, because it was on top,” Semken says. He worked with fellow university researchers to put an age on the bison by measuring the width of its horns.

Semken says they applied the length to a graph that a researcher made several years ago. According to that graph, the size of the bison tapered off after the last ice age, and then increased a little again and then tapered off. “And the width measurement in there says this specimen is about 5,000 years old. And we’re talking in geologic terms here so this could be plus or minus 5,000 to a thousand years,” Semken explains.

Semken says the specimen is in great shape. “In eastern Iowa it is very rare to find a skull this complete in the river. You find them from time to time in western Iowa,”Semken says. “Probably because there were more bison out there at the time — the last 10,000 years or so. And also because the rivers tend to get lower there during the summer, and so more sandbars get exposed and people find them.”

Semken says there are people who collect fossil vertebrates, but he isn’t sure how much this fossil might be worth. “I don’t know, you go to the gem and mineral shows and you see a mammoth tooth for 50 dollars on one table and 200 dollars on another table, and at the end of the show they are both still there. So, I can’t put a dollar value on something like that,” Semken says.

But he does know that the find is valuable in adding to the scientific knowledge of the bison. “One specimen, plus another specimen, plus another specimen, it really adds up to a statistically significant sample over the years. And so this will go into that database and as time goes on we may be able to better define the age of these bison from their horn core width,” according to Semken.

He says he sees lots of fossils brought in every year by people who are out on the river, but nothing quite like this one.