Anderson will update the Porcupine Cave findings in a public lecture at the museum on September 20.
How did all these animals end up in the cave?
Some fell into it through holes in the ceiling. Others lived inside the limestone cavern and some were dragged in by predators, Graham said. Their remains became embedded in the layers of dirt, gravel and rock that periodically washed into the cave or fell from its ceiling.
Some of the debris fell through ceiling holes like sand pouring through an hourglass, depositing a cone-shaped pile directly beneath the hole.
These "talus cones" are the main targets of the paleontologists, who use paint brushes and plastic scoops to gingerly remove about four inches (ten centimeters) of dirt per day from a square, sandbox-like enclosure three feet (one meter) on a side.
Every four inches (ten centimeters) of dirt represents roughly 2,000 years of cave history, Graham said.
Volunteers use tweezers to pull tiny orangish jaws, leg bones and twig-thin ribs from the dirt, placing them in film canisters for safe keeping.
Copyright 2001 The San Francisco Chronicle