Freeway Work Yields Rare Bones : Paleontology: Fossils are found at three separate sites during construction for extension of California 52.

Caltrans employees and paleontologists announced Monday that they had uncovered a nearly complete skeleton of a 47-million-year-old ancestor of the camel--a species never discovered before.

The fossil find, part of a rich cache of bones discovered during construction of a freeway extension in Tierrasanta, will let scientists peer into the world of the Earth’s earliest mammals.

“We are talking about way back to the dawn of the evolution of mammals,” said Thomas Demere, head of the paleontology department at the San Diego Natural History Museum.

The paleontologists found remains of several mammals that foraged the area for plant food during the mid-Eocene age. The discoveries include about half a dozen partial skeletons of the rhinoceros-like brontothere and the protoreodont, a distant cousin of the camel.

Demere said the fossil finds have been made since October, when construction began in Tierrasanta on an extension of California 52--a 10-mile, four-lane connector between Interstate 15 and California 67.

The highway addition, meant to reduce congestion on Interstate 8, also has provided entree into a period of prehistory about which scientists know little.

Although bones of the protoreodont genus had been discovered before, the dog-sized skeleton represents a previously unknown species, Demere said.

“With these finds, we have gradually been able to fill in the picture,” Demere said as he displayed stones with animal skulls and bones embedded in them. Next to the display was an artist’s rendering of how the area appeared during the Eocene epoch.

“If it hadn’t been for the construction, we wouldn’t have found these,” he said.

Caltrans has arranged for the museum to do the paleontological supervision during road construction for about a decade, since a state environmental act mandates that private and public developers in fossil-rich areas work at preserving remains, said Chris White, environmental branch chief for Caltrans.

The remains were found in three sites scattered through the construction area, all in fine-grain sedimentary rock about 30 feet below the surface, White said.

As back-hoe trucks and bulldozers dig and grade the terrain, museum workers search the diggings for tiny flecks of bone, said Steve Walsh, a museum paleontologist. Workers collect rocks from the area and examine then for intact bones.

Some rocks are broken into baseball-sized chunks to speed analysis. Others are soaked in water, which softens the rock into a clod of sediment, then passed through a screen strainer while scientists look for durable remains such as teeth, White said.

White hunkered over a wash basin at the construction site and slung a handful of sifted sediment onto a sludge heap, then began poking through a mound of white-flecked stone.

“Doesn’t look like much,” Walsh said. “But these little chips tell you there’s bones around. . . . With some luck, we find ‘em.”

Caltrans paid for the paleontological work in Tierrasanta--at a cost of about $15,000 for the digging, analyzing and preparing.

The museum has made significant finds during construction work on California 78 in Carlsbad and on building sites in Chula Vista south of San Diego. The discoveries have made San Diego County the site of the “richest assembly of fossils west of the Rocky Mountains,” Demere said.