The Thescelosaurus moved stealthily along the seashore. Stretching about 12 feet long and weighing about 500 pounds, the thickly muscled dinosaur was probably looking for food — or trying to avoid becoming a meal.

Featuring prominent bony eyebrows and a pointy beak, Thescelosaurus plodded along on two feet with the bulk of its body leaning forward while a long tail stretched backward for balance. Suddenly, the dinosaur lifted its head and looked around, alarmed as the calm was broken by a series of unnerving natural forces.

The ground started shaking with intense vibrations while water in the nearby sea sloshed about in response. The sky filled with burning embers, which drifted down and set fire to the lush primordial forest.

Thescelosaurus panicked and looked to flee — but it was too late. Everything changed in a heartbeat as a 30-foot-high wave of mud and debris came racing up the seaway from the south, sweeping away life and limb in the process. The dinosaur was caught in the destructive deluge, its leg ripped off at the hip by the devastating surge.

That moment — 66 million years ago at the end of the Cretaceous period, when an earth-shattering asteroid ended the reign of the dinosaurs — is frozen in time today through a stunning fossil found last year at the Tanis dig site in North Dakota. This perfectly preserved leg clearly shows the skin, muscle and bones of the three-toed Thescelosaurus.

Scientists disc