Storms bring forth prehistoric treasures

On Thursday, on a remote beach in Santa Cruz County, scientist Giancarlo Thomae found this ancient tooth, possibly 10 million years old, from a Meglodon, a 60-foot version of a Great White shark -- scientists and beachcombers have found many ancient fossils since the big storms on the Pacific Coast in December eroded sandstone. less On Thursday, on a remote beach in Santa Cruz County, scientist Giancarlo Thomae found this ancient tooth, possibly 10 million years old, from a Meglodon, a 60-foot version of a Great White shark -- scientists ... more Photo: Giancarlo Thomae Photography / Giancarlo Thomae Photography Photo: Giancarlo Thomae Photography / Giancarlo Thomae Photography Image 1 of / 7 Caption Close Storms bring forth prehistoric treasures 1 / 7 Back to Gallery

In the wake of December’s storms, treasure hunters and scientists have found fossils on beaches and in sandstone cliffs in the Bay Area and elsewhere along the Pacific Coast that date back anywhere from 5,000 to 10 million years.

On Thursday, scientist Giancarlo Thomae found a megalodon tooth on a public beach in Santa Cruz County that could be as many as 10 million years old. The 60-foot great white shark was one of the largest and most powerful predators in Earth’s history. Earlier, Thomae found a great white shark tooth estimated at 4 million years old.

Other recent finds include the tooth of an extinct mammal (Paleoparadoxia) that was similar to a hippopotamus, ribs from an extinct Steller’s sea cow, and teeth from an extinct species of sea lion and 20 species of ancient sharks. Many date back millions of years — some perhaps more than 10 million.

Another find this month that was verified Friday was a bison tooth that was estimated to have lived about 5,000 years ago. The extremely rare find was made in the foothills of the Santa Cruz Mountains by scientist Giancarlo Thomae, a marine biologist from Santa Cruz and Chronicle field scout who also found the megalodon tooth.

Historic finds like this have occurred for years and often peak after major Pacific storms. For instance, a tooth from a saber-toothed cat (known by most as a “sabertooth tiger”), likely more than 10,000 years old, was found by national park ranger Steve Prokop in the cliffs at Fort Funston in San Francisco.

The big Pacific storms trigger the emergence of such items when high amounts of wind-driven rain pound the coastal bluffs and west-facing mountains.

“What happens is the heavy rain, wind and runoff erodes mountain gullies, creek beds and coastal bluffs,” Thomae said. “That can uncover fossil deposits in ancient sandstone formations. In the coastal hills, floodwaters can carry the fossils down creeks and into the ocean. The hydraulic action of the surf zone then digs them up and then, in a high tide, deposits them on the beach. That’s one way it can work.”

Heavy rain treasure hunt

In addition to beaches, other sites where fossils have been discovered include in volcanic ash deposits in cliff walls that face the beach, private quarries and the edges of eroded streams as floodwaters recede, Thomae said. That is how Thomae found the ancient bison tooth last week as he searched the edge of an ancient sandstone formation in the Santa Cruz foothills. “It’s an extremely rare find,” he said.

Note that it’s illegal to collect anything on state and federal beaches and parks, and if you make a treasure find within a park’s boundaries, Thomae suggests that you take a photo and show it to a ranger.

The best region for the oldest finds are the foothills of coastal mountains, but the treasure hunt can be difficult, even for scientists.

The highest numbers of recent discoveries have been in the foothills of Santa Cruz County, where it has already rained up to 25 inches. It is an area scientists have identified as once being the sea floor, and they have found marine deposits roughly 10 million to 12 million years old. That is why most of the fossils discovered in this area are from ancient and extinct marine species, Thomae said.

Even a piece of a giant tooth of a megalodon, like the one Thomae found on a remote beach, is considered an archaeological treasure. Megalodon, about three times the size of a 20-foot, 6,000-pound great white shark, is probably the closest thing to a perfect eating machine that has ever lived on Earth.

Millions of years old

An even rarer find was the discovery of a piece of tooth from Paleoparadoxia. This was an aquatic mammal that resembled a hippo, which could walk the sea bottom and lived on the Pacific Coast roughly 10 million to 20 million years ago.

“We believe less than 10 and perhaps only five or so skeletons of Paleoparadoxia have been found,” Thomae said. “One was found almost intact on the Peninsula when the Stanford Linear Accelerator was built in the early 1960s.”

Most of the fossil finds along the coast’s beaches and cliffs, he said, are post-Ice Age — that is, roughly 5,000 to 10,000 years old.

At Fort Funston in San Francisco, for instance, if you study the cliff walls that face the sea, the persistent few can find what looks like a white, chalky substance, about a foot across, in the sandstone. When it eroded from heavy wind-driven rain, a tooth from a saber-tooth emerged, Prokop, the national park ranger, said.

“That white chalky rock is a vein of volcanic ash,” Prokop told me at the time. “It was created from a historic eruption of Mount Shasta, 300 miles north, and was carried in the flow of rivers and deposited here.”

Another scientist, Tom Hesseldenz, said a blend of volcanic events, sea level fluctuations and geologic uplifting could be responsible for the discoveries of many fossils on the Bay Area and central coasts.

“In many cases, it’s likely that preserved remains like a shark tooth settled out in the ocean, or that of a mammal like the tooth of a saber-tooth settled in an ancient river valley,” Hesseldenz said. “It fossilized and then ended up above sea level due to sea level change and uplifting.”

“San Francisco Bay is only 5,000 years old,” he said. “During the height of the most recent Ice Age, the coast of the Bay Area was out at the Farallones. What is going on is very complex but incredibly fascinating.”

It has turned the Bay Area and Santa Cruz beaches, cliffs and coastal foothills into sites for one of nature’s greatest treasure hunts.

Tom Stienstra is The San Francisco Chronicle’s outdoors writer. E-mail: tstienstra@sfchronicle.com Twitter: @StienstraTom