In sizes hard to imagine, they stomped across landscapes. They grew horns, hoods, specialized claws, and other bizarre bodily features. And after dominating the Earth for millions of years, they mysteriously disappeared.

The enigma surrounding dinosaurs seems grand enough to suit any fantasy. But fossils don’t lie — these otherworldly animals were once very real, and they continue to captivate enthusiasts of all ages.

“There’s this timeless interest in these creatures ever since people in the mid- to late-1800s started discovering their bones and tried to figure out what kind of creatures these were,” said “Fossil Guy” Don Johnson, the founder of the Eastern Iowa Paleontology Project. “It’s something that’s rooted in reality but that’s lost. By studying fossils, we do our best to build a picture of the environment in which they lived and imagine, I suppose, time-traveling back to see what those worlds were like.”

Johnson, teaming up with the University of Iowa Museum of Natural History, will present the interactive event, titled “Twilight of the Dinosaur Age,” as part of the “Fossil Guy” paleontology program. The event will take place 2 p.m. Saturday in Macbride Auditorium. Admission is free.

A 10-year-old series, Museum Education and Outreach coordinator Sarah Hogen said it is one of the museum’s most popular and enduring programs, attracting an average of 50 to 100 visitors to Johnson’s various lectures and vast fossil, replica, and model collection.

“Probably the best part of this program is that it is so interactive — they get to have some hands-on time with the collection,” Hogen said. “He really tries to say paleontology isn’t just about dinosaurs; there are different time periods and animals that we can look at.”

Although Johnson does give presentations on other fossil vertebrates and time periods, his dinosaur programs are particularly popular, including his dinosaur bones and teeth, Tyrannosaurus rex jaw bone, and replica of skin that was preserved on a duckbilled dinosaur.

“When you run your hand across it, you can feel the bumpy scales; I tell the kids to imagine they’re petting a dinosaur,” Johnson said about the replica. “We just pose questions and try to learn more about the dinosaurs that lived during the Late Cretaceous in what we call the ‘twilight’ of the Dinosaur Age.”

UI Professor of geosciences Christopher Brochu, who teaches the Age of Dinosaurs course, said he, as does Johnson, believes introducing dinosaur diversity to young people can encourage further exploration.

“I think it’s important to cultivate an interest for children in science at an early age, paleontology among all of the other sciences,” he said. “If you’re dealing with a group of children, and you’ve only got one hour, what’s a good way to make an impression? Well, bringing in a cast of a fossil that’s really big is one way to do that.”

Hogen said audience responses to the “Fossil Guy” discussions are largely positive, especially among children.

“You have these very small kids asking him pretty in-depth questions about things they’ve read,” she said.  “It’s just amazing what kids absorb when they’re interested in that.”

This curiosity, Johnson said, got him hooked on paleontology as a kid, and that endured into his adulthood, prompting him to take on the identity of “The Fossil Guy.”

“I think it’s a connection between fantasy and reality,” Johnson said. “You can learn about dragons and ancient monsters that really don’t exist, but these are creatures that were large or very unusual that really did walk on the Earth, and there’s nothing really like them around today. That captures the imagination not just of children but of many adults as well.”