Scientists went back to work Thursday at one of the world's richest Ice Age fossil sites, digging the tooth of a five-foot dire wolf and the toe of a sabertooth tiger from the sticky prehistoric asphalt near Wilshire Boulvard.

About 10,000 years before the arrival of mammoth traffic jams, the two beasts likely got stuck in the goo at La Brea Tar Pits while hunting a camel, horse or ground sloth, said John Harris, chief curator and head of vertebrate studies at the Natural History Museum of Los Angeles County, which oversees the site.

Thousands of other animals made the same fatal mistake, leaving a treasure trove of well-preserved bones, plant remnants and microorganisms.

Excavation work began in 1915 and has been done every summer since 1969 to the delight of children and other visitors who watch from a glass-enclosed area overlooking the 14-foot deep pit.

"It's one of the, if not the, richest Ice Age excavation sites in the world," Harris said.

The work lasts from July 1 to Sept. 10. During the rest of the year, visitors to the nearby Page Museum can watch scientists behind a glass window scrub fossils found during the excavation.

The site is a favorite among children who let their imaginations wander as they watch tar-covered excavators move along gangplanks.

Through a fence at the park, 7-year-old Ben Guerra and his 9-year-old sister Rhemy got a peek at the dig.

"I like to imagine how the animals attacked the other animals who were stuck in the tar," Ben said. "Maybe they thought it was water and went to get a drink."

Last summer, scientists unearthed some 3,000 specimens from Pit 91, including bones of coyotes, horses and giant ground sloths.

While the larger bones enthrall most visitors, the remains of tiny insects, animals and microscopic organisms can be equally exciting for scientists.

While alive, those creatures were less likely to wander far from the site. As a result, their remains reveal a great deal about the character of the area tens of thousands of years ago.

"A mouse found here probably spent its whole life within 20 acres," said Chris Shaw, the site's project coordinator and collection manager at the Page Museum.