SPRINGFIELD, Missouri (AP) -- The bear that left a 3-foot-long claw mark in an Ice Age clay bank was the largest bear species ever to walk the earth, about 6 feet tall at the shoulder and capable of moving its 1,800 pounds up to 45 miles per hour in a snarling dash for prey.

The claw mark by the extinct giant short-faced bear still looks fresh today in a southwest Missouri cave that some scientists are calling a national treasure -- an Ice Age time capsule sealed for thousands of years.

Discovered accidentally five years ago on the outskirts of Springfield, Riverbluff Cave is slowly yielding its fossil treasures as a small team of scientists and volunteers gingerly explores it while trying to preserve a rich bed of remains, from bones to tracks and dung.

"We found 5,000 microfossils in just one 1-foot by 2-foot block of clay," said lead paleontologist Matt Forir, the naturalist for Springfield-Greene County Parks.