The bear that left a 3-foot-long claw mark in an Ice Age clay bank was the largest ursine species to walk the Earth, about 6 feet tall at the shoulder and capable of moving its 1,800 pounds up to 45 mph 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 that include bones, 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.
Remains in the cave date back at least 830,000 years and possibly more than 1 million years. At some point at least 55,000 years ago, it was sealed by rocks and mud until a construction crew blasted a hole in one end while building a road on Sept. 11, 2001.
The first major excavation is set for this fall after years of carefully surveying the 2,000-foot-long cave and collecting remains from the cave floor or protruding from the limestone and clay walls.
Just based on what was on the surface, the finds so far include mammoth and horse bones and beds clawed out of the clay by the short-faced bear, possibly while denning with cubs. Peccary tracks are the first proof that herds of the pig-like animals roamed in caves rather than just being dragged in by predators.
There are tracks of large cats, possibly saber-toothed tigers or American lions. Foot-long shells of previously unknown turtle species stick out of a wall.
Forir said every discovery raised new questions. Mammoth bones and a juvenile tooth dated around 630,000 years ago came from one of two species, and it will require more adult remains to tell which one it is. He hopes the excavation will provide answers.
"We either have the oldest wooly mammoth in North America or the youngest Meridian mammoth. Most of the stuff in this cave is like that, always raising more questions," he said.
Paleontologist Larry Agenbroad, who heads a major mammoth excavation project called The Mammoth Site in South Dakota, said the number of remains of large animals and the fact that Riverbluff Cave was sealed like a time capsule made it a rarity.
"This is a national paleontological treasure," he said.
Greg McDonald, senior curator of natural history for the National Park Service, said Riverbluff Cave offered rare insight into Ice Age ecology. By combining animal bones with other traces, including tracks and dung, it can show how Ice Age animals lived, what they ate and what killed them off.
"It's a unique combination of traces and the quality of preservation that makes it such a phenomenal site," McDonald said. "It's probably going to become a major reference site that will help us better understand the remains we have at other sites."
If research confirms that dung in the bear beds is from the short-faced bear, it would be a first and could provide real clues about what the bears ate, McDonald said.
Forir said the short-faced bear was the largest land predator of its time, roaming much of North America and catching its prey with a jaw power of more than 2,000 pounds per square inch. Its name comes from a shortened muzzle, more like a lion's than a black or brown bear's.
"It was the T-Rex of the Ice Age," Forir said.
The cave remains closed to the public to preserve its remains. After an attack by vandals, it was sealed by the county behind locked metal doors equipped with an alarm.
But with the help of the Springfield-Greene County library system and Ozarks Technical Community College, Forir installed a fiber optic network that lets him broadcast pictures from the cave for school classes and the public.
"This is where the Ice Age meets the Space Age," he said.
The cave has also spawned another educational project, Missouri's first natural history museum.
Forir won a grant to build a 4,000-square-foot building near the cave that will house a new Natural History Museum of the Ozarks. The museum, which should be constructed by early 2007, will showcase the cave's findings as well as regional natural history.