Every so often, creatures would get bogged down in pools of water and asphalt that seeped from underground crude oil deposits, and die of dehydration or starvation. Stranded animals that appeared to be easy prey then became a trap for predators that also got stuck in the ooze.
In 1913, the predecessor to the Natural History Museum of Los Angeles County launched a two-year project to uncover only the best-preserved mammal bones, largely ignoring everything else. Though the early digs gave scientists a glimpse into the types of animals that roamed, there was still much to be learned.
After the early missteps, scientists in 1969 decided to focus on pulling everything out and revisited a tar pit dubbed Pit 91 to do a more detailed excavation. For nearly 40 years, work at Pit 91 dominated the Page Museum's efforts as visitors gawked from a viewing platform.
Museum officials temporarily halted digging at Pit 91 several years ago to concentrate on an unexpected trove of Ice Age fossils that was found during the construction of an underground garage next to the tar pits, located some 7 miles west of downtown Los Angeles.
"I can't think of any other site that is as rich," said Sarah George, executive director of the Natural History Museum of Utah.
Every time a foundation is dug, "more old blocks of tar filled with fossils came out of the ground," said George, who used to work as a curator at the Natural History Museum of Los Angeles County.
Despite a century of digging, scientists still can't agree on how the Ice Age beasts became extinct. Some suggested that the prehistoric predators may have competed with humans for similar prey and that carnivores ate carcasses out of desperation. But Larisa DeSantis of Vanderbilt University said dental studies of saber-toothed cats and other carnivores suggest they were "living the good life" before they became extinct.
Museum excavators plan to leave some fossils buried — in case better tools are invented to study them in the next century.
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