(Aaron Atencio)

A rich cache of ice age fossils plucked from a Carlsbad construction site this summer is helping paleontologists at the San Diego Natural History Museum to better understand climate change and why animals become extinct.

The ancient bones were found at the 60-acre Quarry Creek site, where more than 600 houses, apartments and condominiums are being built just south of state Route 78 between El Camino Real and College Boulevard.

None of the skeletons is complete, but that’s part of the job for paleontologists. In the best example in the collection, the bison skull, only one horn was recovered.


“The bulldozer hit the other horn,” fossil preparer Nikki Anderson said Wednesday at the museum. “We call that the scraper tax. It’s the cost of getting it (the fossil) out of the ground.”

The other horn is most likely buried somewhere on the site, but the bison skull that was dug up and hauled away is more than 80 percent complete. It arrived at the museum in a “field jacket,” a plaster-wrapped cocoon of soil and bones that included a full upper jaw, some vertebrae, at least one rib and other bones.

On Wednesday, Anderson continued the painstaking work of brushing and scraping away the “matrix,” which is the soil and sediment around the fossils.

“You find the bone, then follow the bone,” she said, using a small knife and a brush to scrape away material, and an occasional small dab of glue to keep a bone chip in place.


The skull is believed to be from a giant ice age bison, a species that lived between 50,000 and 100,000 years ago.

× A rich cache of ice age fossils plucked from a Carlsbad construction site this summer is helping paleontologists at the San Diego Natural History Museum to better understand climate change and why animals become extinct. The ancient bones were found

It is only the second such bison skull ever discovered in San Diego County. The grass-chewing animal stood more than eight feet tall at the shoulders and weighed more than two tons.

“It’s more evidence of the environment that existed here in the ice age,” Anderson said.


Also collected were a 42-inch-long mammoth humerus bone — the equivalent of a human’s upper arm bone — and a fully articulated mammoth foot, though it’s unknown whether the foot and the humerus were from the same animal. Other fossils include an ice age pond turtle, some teeth from ancient horses and at least one mastodon tooth.

Paleontologists say the Carlsbad discoveries may shed new light on the plants and animals that lived in San Diego County more than 50,000 years ago, and why they are extinct today.

The bison fossil could help scientist learn more about the migratory patterns of prehistoric animals, said Kesler Randall, the museum’s collections manager.

“Bison didn’t evolve here in North America.” Randall said. “They migrated from Asia.”


Scientists could use radiometric dating to more closely determine the age of the fossils, he said, which would add more information about migratory patterns.

“These are large animals that lived along the coast,” Randall said. “Now they are no longer here, so we have to ask what happened to change that?”

Further clues may be discovered as scientists study the soil and sediments collected with the fossils.

The California Environmental Quality Act requires all major construction projects to be monitored for potential paleontological discoveries. Veteran paleontologist Brad Riney, who was monitoring the Quarry Creek site, said the soil and terrain there made it likely that fossils would be found.


“It’s like a layer cake with the older parts at the bottom,” he said. Layers range from cobbles, to gravel, to fine-grain sand. The bison skull was found in sandy soil at the 120-foot elevation, he said, and both mammoth fossils were found in soil with more clay content about eight feet higher.

Paleontologists will continue to work on the Quarry Creek fossils at least through October. Visitors can watch the process on the third floor of the Natural History Museum in Balboa Park.