March 11, 2017



At first, the bones are hard to see in the chunk of fused pebbles that Patrick Sena is holding. But in a minute they appear: a piece of jaw with a yellowing tooth, and a bleached femur whose round end could hide under the head of a pin. They’re 28.5 million years old.

Sena, a paleontologist with the San Diego Natural History Museum, looks up and squints at a hillside in the distance where scrapers and front-end loaders are noisily working. In a few years, these 250 acres will be Otay Ranch Village 3, with 1,200 dwelling units, an elementary school, a park, a swim club, and industrial and commercial spaces. Whatever Oligocene treasures the land may hold — other than the inconsequential ones in Sena’s hand — will be beyond reach.

For the next few weeks, however, the hunting will be good. Sena hopes to bag fossil tortoises, camels and rhinos, along with numberless small carnivores like the one whose bones he’s holding. “They will be cutting down through the richest part of the Otay Formation. That’s why I need to be out here.”

It’s the law. It’s also a terrific deal for the San Diego Natural History Museum, which gets to keep whatever is found.

In California, when governmental agencies, developers and even private landowners dig in fossil-rich soil, a paleontologist must keep an eye on the work. Since 1995, Sena’s museum has provided this service for a fee, competing with private scientific contractors. Any significant fossils that are found must be curated, catalogued and transferred to a museum or university, although in certain circumstances landowners can retain ownership.

This arrangement has filled the San Diego museum’s display cases as well as its coffers. In fiscal 2016, the museum’s PaleoServices business provided $1.35 million, roughly 12 percent of the institution’s operating revenue, and salvaged specimens now make up 75 percent of the institution’s fossils. This win-win arrangement may be unique among American natural history museums.

“I don’t know of any other museum doing it the way San Diego is,” said Scott Foss, senior paleontologist at the U.S. Bureau of Land Management in Washington.

“They have the perfect combination of lots of construction, the need to mitigate, expertise and the ability to display,” said Kirk Johnson, director of the Smithsonian’s National Museum of Natural History.

Other museums have occasionally struck arrangements of the sort that San Diego has institutionalized. For example, the Denver Museum of Nature and Science made about a half-million dollars from survey-and-salvage contracts for interstate road projects in the 1990s, said Johnson, who worked there at the time. More often, the museum did consulting work for free. When construction at a resort uncovered skeletons of mammoths and mastodons in 2010, the museum hustled to raise $1 million to recover them.

At a Chula Vista, Calif., construction site in 2000, workers from the San Diego Natural History Meseum’s PaleoServices unit excavate the fossilized skull and vertebral column of a whale that lived about 3.5 million years ago. (Courtesy of Thomas Deméré)

There’s a long history of salvaging fossils from construction sites.


In 1673, a London apothecary and amateur archaeologist, John Conyers, found a tusk of an extinct elephant-like animal during work to divert the River Fleet into an underground culvert. The specimen was eventually acquired by Hans Sloane, whose collection started the British Museum. In the United States, a mastodon skeleton was found in New York in a pit dug to extract limestone fertilizer. The discovery is depicted in Charles Willson Peale’s “Exhumation of the Mastodon” (1806-1808).



Thomas A. Deméré, the 68-year-old head of PaleoServices, is one of the founders of the field. He has a doctorate from UCLA and originally worked in the oil industry. (Fossils help identify geological formations that may hold oil.) He found a lot of great specimens but couldn’t publish anything about them because that might reveal petroleum formations to competitors. “Everything was a big secret,” he said. “It was kind of nonscientific.”

When local governments in Southern California started requiring protection of fossils in the 1980s, Deméré created Paleo­Services while also working part time at the museum. In 1995, the museum took over the company and hired him full time.

The arrangement has proved unusually fruitful for the 142-year-old museum, whose focus is the natural history of Southern California and Baja California.

In San Diego County, the geologic record is most complete for the past 75 million years, with the Pliocene (the past 4 million years) and the Eocene (40 million to 50 million years ago) especially well represented. A building boom that has lasted half a century guarantees there’s always lots of excavation to monitor.

Before the 1980s, the museum’s fossils came from around the world — a “stamp collection,” in Deméré’s words. The arrival of salvage paleontology, ironically, has made the holdings more scientific, allowing scientists to fill in many blanks in the region’s prehistory. The museum’s collection has 154 holotypes — the specimen from which a new species is described — and 50 of them were found in construction sites.

Mitigation paleontologists don’t gather up all the fossils that a road project or housing development uncovers. Instead, they collect samples while keeping their eyes out for marquee items, such as the 3-million-year-old whale skull found during the construction of a bike trail last fall.

The collection strategy is often “driven by a research question,” said Shelley L. Donohue, PaleoServices’ report writer. As an example, she cites the Sycamore Landfill, “a giant hole that will be filled with trash.” Seven years of digging has allowed scientists to answer hard questions such as how ecological niches were filled (or left empty) over the eons. At the moment, there’s a particular interest in insectivorous mammals.

PaleoServices field workers normally haul a ton or two of material away from a site in pickup trucks and sift it for fossils. Occasionally, dump trucks are used. The museum collected 25,000 pounds from one place in the 1990s, looking for prosimian primates, which it found.

This moveable feast of fossils means there’s plenty of leftovers. Surplus specimens are given to schools and even to visitors. A construction site in Chula Vista yielded a load of sand dollars, shells and bird bones. Children were allowed to screen the material and keep what they found.

About a dozen researchers visit the museum each year to use the collection. About 50 papers, from both in-house and outside scientists, have been written based on the museum’s holdings in the past 30 years.

There is a downside, however, to collecting fossils with construction equipment.

“The paleontological monitor noticed an explosion of white when the road scraper tagged that,” Deméré says, pointing to the upper foreleg — the humerus — of a Columbian mammoth now awaiting curation back at the museum’s lab. There’s an unnatural flatness to the end of the bone. The missing piece — a bulge called a condyle — was the price of discovery.

In an exhibit of marine mammal fossils, the top of the skull of an extinct gray whale is prosthetic. Another whale skull is missing part of its underside. The chances of a big, display-worthy piece of skeleton being recovered undamaged are pretty small.

The people at the museum call it the “scraper tax.”

Collection’s manager Kesler Randall and curator Thomas Deméré work together with staff at the Naval Medical Center San Diego to place the partial skull of a Columbian Mammoth (Mammuthus columbi) into a CT scanner. (Robert Rutherford/San Diego Natural History Museum)


In San Diego County, a paleontologist must be present if construction at a fossil-bearing site will move more than 2,500 cubic yards of soil. At Otay Ranch Village 3, 7 million cubic yards will be moved. Pat Sena, who is 48, is going to be there awhile.

Bulldozers and road scrapers — four and eight of them, respectively — were shaving the top off a ridge on this particular day. Their target was a layer of volcanic ash called bentonite, which is a poor material to build houses on. Dump trucks deposited 28,000 cubic yards of the material down in swales at the bottom of the hill each day.

This was once a coastal marsh, with braided streams flowing into a sea. Deluges scoured deep channels. Heavy material from uphill and inland — including the bodies and bones of living things — were deposited there. Most of the skeletons in the museum’s collection are incomplete because the animals weren’t buried where they died. The few terrestrial dinosaurs in the collection bear evidence of having been washed into the ocean. An ankylosaur (armored dinosaur) and a hadrosaur (duck-billed dinosaur) each have oyster shells stuck to their fossil bones.

The excavated ground at Otay Ranch is a mixture of clays and cobbles in gray, white and tan. It’s hard to make out the walls of the ancient channels unless you know what to look for. Sena does. He started young, accompanying his geologist father on outings to search for uranium deposits, work that involved well-logging — recording characteristics of geological formations.

“While he would be well-logging, I’d be collecting fossils. I used to carry a geology book around with me in first grade,” he said. “Nothing’s changed.” A former corpsman in the Marines, he joined PaleoServices 20 years ago. He doesn’t have a college degree. What he does have is an eye for small objects, up close and at a distance.

“He can find fossils where nobody else does. He sees patterns. He just has a feeling for the earth,” Deméré said.

The law requires that grading be suspended “upon discovery of fossils greater than twelve inches in any dimension.” There are few discoveries that big. When there are, they’re removed en bloc, field-jacketed in plaster and taken back to the museum for definitive uncovering.

Such rules sound like a recipe for endless delay, but apparently they aren’t. “Very rarely do we have to move out of an area for any length of time,” said Lance Dougherty, the jobsite foreman for the company shaping the land at Otay Ranch. “Sometimes it’s an hour, sometimes it’s half a day. It doesn’t slow us down because we can work in another area.” He acknowledged, however, that it’s sometimes inconvenient.

For his part, Deméré knows that keeping fossils safe isn’t a high priority for government.

“Obviously, there’s a cost associated with regulations. There’s a cumulative effect when you stack them all up. But I’d hate to see us take a big step backward.”

As a way to thank property owners, builders, excavation contractors, bulldozer drivers, environmental planners and city staff, the museum holds an annual party to display what has been collected in the previous year.

“The idea is that, without mitigation work, all this would be lost — everything from bison heads and whale jaws to mice teeth and tiny shells,” Deméré said.

“One of the showstoppers last year was fossilized foraminifera,” said Donohue, the report writer. “You have to see them through a microscope,” she said of the tiny calcificed organisms.

Some property owners don’t need thanking. During the construction of a high-rise at Thomas Jefferson School of Law in downtown San Diego, equipment operators found a mammoth, a gray whale and a shell bed in sequential strata. “The dean was thrilled. He is a history buff. And Jefferson collected fossils,” Deméré said. The parking levels under the building are named for the discoveries at each depth.

PaleoServices monitors discovered this skeleton of a 3 million-year-old fish during trenching excavations for a sewer line. (Antonio Cusumano/San Diego Natural History Museum)


Paleontological digs are famously slow operations. Scientists sprawl on the ground, uncovering objects with dental picks and sable brushes as if they had all the time in the world.

Salvage paleontology is different. It’s more closely related to chain-saw sculpture and speed chess. And birthday mornings.

In the trailer at Otay Ranch, the project superintendent, Robert Greninger, sat at a desk beneath a map of the development. The house lots on its not-yet-built curving streets look like the vertebral bodies of long-necked, long-buried lizards.

When Deméré greeted him, Greninger mentioned the 10-year-old son of his boss.The boy loves visiting the site. But it isn’t to see the machines with eight-foot tires. It’s to see “what Mr. Pat has found.”

Of such encounters are paleontologists born.