Suddenly we noticed the teeth – a whole row, large, grey and pointed.

During a multi-day hike in Badlands National Park, our girls were determined to find a fossil and kept stopping to search the ground.

They looked for differences in texture, trying to spot smooth bones as we walked along a ledge of the park’s distinctive rock formations. Wind and rain erode the rocks of the Badlands at a rate of about an inch a year, continually exposing fossils that are millions of years old.

By this point, my husband and I were getting a little tired of urging our kids (ages 7 and 10) to keep walking, so we weren’t expecting much when our youngest, Emilia, called out that they had found something off the trail. Our oldest, Elise, had noticed a small, white fragment of bone near where they had stopped for a water break. Emilia looked closer and realized that a much larger piece was stuck in the cracked, crumbly ground.

When we saw these teeth, we realized that they had discovered the jaw and perhaps even the entire head of an ancient creature. The whole family was very excited and told the park rangers about the discovery.

To report on the girls’ discovery, we participated in the park’s Fossil Finder program in South Dakota, a citizen science project. The experience was a highlight of our stay in the otherworldly landscape of the Badlands, where we also stargazed, spotted bison and went on hikes like the Notch Trail, with its ascent via a wooden ladder.

We later learned that the girls had discovered the fossilized jaw of an oreodont—a prehistoric creature that paleontologists say probably looked like a cross between a camel, a sheep, and a pig.

The park’s Ben Reifel Visitor Center features an active paleontology lab, where we watched scientists and interns prepare fossils and learned about the ancient mammals that lived here millions of years ago.