Three-toed horses, ancient camels, and barrel-bellied rhinos are just a few of the species long extinct in North America that paleontologists have found buried together in Nebraska.

The volcano that killed them erupted hundreds of miles away in southern Idaho, spewing a blanket of ash over much of what is now the western U.S. Some of the animals uncovered at Ashfall National Park near Royal, Neb., were killed instantly; others suffocated slowly, as the ash that hung in the air filled their lungs.