Rare fossil of ancient dog species discovered by San Diego paleontologists

Sometime around 14,000 years ago, the first humans crossed the Bering Strait to North America with canines, domesticated dogs they used for hunting, by their side.

But long before the canines arrived here, there were predatory doglike canid species who hunted the grasslands and forests of the Americas. A rare and nearly complete fossilized skeleton of one of these long-extinct species was recently discovered by paleontologists at the San Diego Natural History Museum.

This fossil belongs to a group of animals called Archeocyons, which means “ancient dog.” It was embedded in two large chunks of sandstone and mudstone unearthed in 2019 from a construction project in the Otay Ranch area of San Diego County.

The fossil dates to the late Oligocene epoch and is believed to be 24 million to 28 million years old.

While the fossilized remains are still awaiting further examination and identification by a canid researcher, its discovery has been a boon for the San Diego museum’s scientists, including the curator of paleontology Tom Deméré, post-doctoral researcher Ashley Poust and curatorial assistant Amanda Linn.

Because the existing fossils in the museum’s collection are incomplete and limited in number, the Archeocyon fossil will help the paleo team fill in the blanks on what they know about the ancient dog mammals that lived in the area we now know as San Diego tens of millions of years ago.

Did they walk on their toes like today’s dogs? Did they burrow in the ground or live in trees? What food did they prey on and what animals preyed upon them? How did they relate to extinct doglike species that came before them? And, potentially, is this an entirely new undiscovered species? This new fossil is providing SDNHM scientists with a few more pieces of an incomplete evolutionary puzzle.

“It’s like you’ve found a tree branch, but you need more branches to figure out what kind of tree it is,” said Linn, who spent nearly 120 hours from December through February partially uncovering the fragile, and in some places, paper-thin skeleton from the rock. “As soon as you uncover the bones, they start to disintegrate ... I used a lot of patience, and a lot of glue.”

Archeocyon fossils have been found in the Pacific Northwest and Great Plains states, but almost never in Southern California, where glaciers and plate tectonics have scattered, destroyed and buried deep underground many fossils from that period of history. The chief reason this Archeocyon fossil was found and made its way to the museum is a California law that requires paleontologists be onsite at major construction projects to spot and protect potential fossils for later study.