When I was a young child in Los Angeles, one of the most terrible things we dared to say to each other was “go play on the freeway.” I learned recently that safely hanging out on the side of the freeway can actually be a fascinating way to play hooky from the office.
Of course I jumped at the chance to visit one of our paleontological sites to see a fossil whale skull before it was fully excavated. Anything that involved wearing a hard hat and safety vest and driving behind the K-rail barriers along Interstate 15 was bound to be a grand adventure.
San Diego sits on rich fossil deposits that go back millions of years. State and federal laws require that paleontologists be present at construction projects to record and preserve important fossil finds. The Museum’s PaleoServices division has more than a dozen expert paleontologists who work to salvage significant fossils during transportation projects and residential and commercial digs. Many of our PaleoServices staff are regularly out monitoring construction sites as far afield as the Antelope Valley and El Centro. Fortunately for me, the whale skull was found on a CalTrans project to build a bike path along I-15 only a short distance from the Museum.
We met in the parking lot of Ponce’s Mexican restaurant and were glad to have paleontologist Rodney Hubscher at the wheel. One of the skills he learned on the job is how to safely pull over on the shoulder of the freeway and back up behind construction barriers while cars and semis are zipping by at full speed.
I-15 cuts through the aptly named San Diego Formation. In the Pliocene, 1.5 to 3 million years ago, San Diego was up to 300 feet under the sea, and the coastline was in the general vicinity of Lemon Grove. The San Diego Formation is a thick sequence of ancient sandstones that were deposited in a large, curved bay about the size of today’s Monterey Bay that stretched from Mount Soledad in the north to Rosarito Beach in Baja California to the south. The sandy cliffs alongside the I-15 freeway were once layers of soft sediment that formed on the ancient bay floor.
Our tour guide for our trip to the Pliocene was Brad Riney, a Museum paleontologist who found his first dinosaur fossil at age 13 and sees the world through a different and ancient lens. I looked at a sandy embankment and Brad saw a “death assemblage” of mollusks and various whale parts. While we were squinting and trying to make out the mostly buried whale skull, Brad found an additional whale vertebra and a rib. When asked about his ability to pick out whales he said “most people see clouds when they look up, I see whales.” To him, the embankment “read like a book.”
Brad explained that these layers appeared to preserve a death assemblage because the clams were mostly represented by single halves of shells rather than intact bivalves. The few intact shells were oriented on their sides, not siphon side up as they would be if the animals had been preserved in life position. He spied a few pebbles and said the shells were probably washed there by storms or carried along with the pebbles in channels incised into the sea floor. Furthermore, a little hand digging in the bank revealed the impressions of ancient mollusk species that are more common in southern areas. Brad interpreted this to mean that the water in this area was warmer 3 million years ago.
On October 17, about two weeks after our visit, our team worked with CalTrans to remove the skull from the bank and transported it to the Museum. Our crew removed the skull in a block of surrounding sedimentary matrix so the painstaking work of fully excavating and cleaning the fossil takes place in the lab and not on the hillside perched over a noisy freeway. The whale skull is currently being prepared in our Paleo Prep Lab at the Museum. It will be identified and join the Museum’s collection so current and future scientists can unlock its stories.
When complete, the new bike trail along I-15 will do more than connect Kensington to Mission Valley. It will provide observant cyclists a ride through time and space, where whales and other marine creatures once lived and died. Elsewhere in the San Diego Formation, paleontologists have found fossil sharks, rays, fin fish, sea birds, and marine mammals such as whales, dolphins, walruses, fur seals, and sea cows. I, for one, will be braking for fossils.
Although the shells had disintegrated, some of the hardened sandstone interiors were preserved in the sandy rock. Here, Rodney points out the inside of a marine snail.
Brad used his detailed illustration to help us pick out the indentations that represent the cranial cavity of the whale skull. The size and shape of the cranial cavity indicates that it was a baleen whale.
Rodney (left) and Brad (right) joined Rebecca Handelsman and me in an onsite selfie.
Posted By President and CEO Judy Gradwohl.