The prehistoric remains of Ice Age horses, mammoths, turtles and a bison have been unearthed at a construction site in southern California.

The treasure trove of fossils were uncovered at the Old Creek Trails work site in Carlsbad, south of state Route 78, in San Diego County. The site is earmarked for more than 600 homes.

The prehistoric bison is only the second ever found in San Diego County,

All the fossils date from the Pleistocene Epoch, and range from 50,000 to 200,000 years old, said Tom Deméré, the curator of paleontology at the San Diego Natural History Museum.

Deméré says the fossils have the potential to tell scientists a great deal about the climate, the environment and ecology in the region at the time the animals were living.

“They are direct connections with the past, an ancient ecosystem that was once common here.”

Large construction projects in California must have a paleontologist on site when large amounts of earth are moved.

Project superintendent John Suster admitted his surprise when the first fossils were unearthed in July. “It’s just rolling hills, nothing special,” Suster said. “I don’t think there’s any way you could have known.”

Work was temporarily halted to allow scientists to carefully remove the finds.

Ure Kretowicz, the chief executive of Cornerstone, the company behind the site development, said the firm had worked closely with paleontologists throughout the grading, which is expected to continue for another two months.

When a possible fossil is found, it is cordoned off and work stops within that area while paleontologists move in.

“We stop everything or go grade another area on the site. Once they’re gone, we start up again.”

The bison fossil, which includes a skull and partial skeleton, is the most unusual and probably the most complete of the larger animals found at the project site, said Deméré. The exact species hasn’t been identified, but is believed to be either a giant bison (Bison latifrons) or an antique bison (Bison antiquus)

“These are big animals, much larger than modern plains bison,” he said.

The specimen has been moved to the museum, where it will eventually be placed on temporary display.

The other fossils include at least two Columbian mammoths, an animal larger than the better-known woolly mammoths that lived in the northern latitudes of North America.