It's like opening a box of Cracker Jack, not knowing what the prize is inside.

That happens today at the Burke Museum on the University of Washington campus, when youngsters will able to crack shale rock to see if there's a fossil inside.

If so, the kids can take it home to treasure — unless it's something extraordinary that needs to be on display.

The fossil hunt is just one activity today at the museum, which hosts its annual Dino Day. Museum staffers will be there to explain paleontology to children and adults, and the museum will offer live demonstrations from scientists including paleontologist Bruce Crowley, who will work on a fossilized Tyrannosaurus rex bone found in Wyoming last year.

"It's a sensory overload for kids who like dinosaurs," said Christian Sidor, a curator of vertebrate paleontology at the museum.

New this year and displayed on a wall is a 21-foot-long ichthyosaur, a fish-shaped reptile that lived in the Mesozoic Era when dinosaurs roamed the land. The ichthyosaur became extinct 90 million years ago and was known for its unique jaw.

The fossil was a gift from the Hart family, of Seattle, which owned a company that ran a commercial real-estate business and has donated many fossils to the Burke Museum.

Today's Dino Day, now in its 23rd year, is presented with partners Northwest Paleontology Association and the Stonerose Interpretive Center in Republic, Ferry County. Stonerose donated the shale rock that kids can hammer apart to look for fossils inside. Some of the fossils could be 48 million years old.

Ron Eng, geology collections manager at the museum, said a fossil find is a treasure for the children. "The discovery is so exciting," he said.

Other activities include the Dinosaur Romp Room, where kids can dress up with dinosaur body parts and chase each other around the room.

An artist will make drawings of dinosaurs.

The museum also will bring in a 9-foot-long ancient marine reptile, still in its crate, and it will be opened to visitors. It is part of the Hart collection and was found in China; experts believe it's 230 million years old.

Susan Gilmore: 206-464-2054 or sgilmore@seattletimes.com