Millions of ancient fossils were discovered underneath a California high school and it's rewriting the state's history. Take a look.

People first uncovered fossils around San Pedro High School in 1936. They were ancient shells belonging to snails and other mollusks from tens of thousands of years ago.

That's why Austin Hendy, an assistant curator at the Natural History Museum of Los Angeles County, wasn't too surprised when a similar bed of shells turned up during construction on the former site of the school's home economics building in 2022.

The shell bed was 120,000 years old. When Hendy got a look at it, he said it was like stepping back in time.

"I could see the shoreline in three dimensions, and I could see all the fossils, all the organisms that were living on that shoreline and washing up on that beach," he said.

The site's shell bed now accounts for the museum's largest collection of fossil shells.

While the shell bed was an exciting find in its own right, the scientists had no idea they had only scratched the surface of the fossil-packed site.

In 2023, Bischoff was visiting the construction site when he realized limestone blocks taken from below the 1936 courtyard contained the remains of animals far more complex than simple mollusks: they were fish and mammal bones.

After hosing off the mud-caked blocks, Bischoff and the construction workers discovered an astonishing amount of fossils.

"The volume of fish bones was remarkable, but coming across baleen whale vertebra was the most amazing," Bischoff said.

The finding kicked off a huge salvage project to record and date the fossils, which turned out to be roughly 8.7 million years old.

The blocks contain everything from extinct dolphins to sea turtles to sharks to impressions left behind by seaweed.

That's because roughly 9 million years ago, Southern California was underwater.

The diverse collection of different animals and plants is special, Hendy said, because it provides experts a better understanding of the California coast's ecosystem during the Late Miocene epoch, millions of years ago.

One fossil was a turning point for Bischoff: the skull of a sandpaper bird from over 8 million years ago.

"Seeing a shorebird, and also large numbers of shoreline horsetail plants, started me thinking of an island beach as the origin of all of the fossil material," he said.

This would suggest there was once an island to the west of the fossil site where the bird may have visited. It started to change Bischoff's ideas on California's geology during the Miocene epoch.

The weight of debris from volcanic eruptions would have collapsed the island's slopes, creating a canyon where the fossils accumulated. Tectonic activity eventually helped the beds reemerge closer to the surface.

There might have been other pieces of land in the area, too. Geologists are studying how and where channel islands might have formed and sunk off the state's coast during this epoch.

Bischoff will get to name the extinct island. He was leaning toward San Pedro Island until his wife suggested he name it after her: Shelley Island. He's been polling people. "I started asking which people prefer, and she is winning by a lot," he said. "The San Pedro students especially side with her!"

The high school wasn't done giving up its secrets. Older fossils lay even deeper beneath the bone bed.

These 8.9-million-year-old rocks included fossilized bones of fish and marine mammals. Experts also found teeth from juvenile megalodons and other smaller sharks.

Megalodons were enormous, three times longer than a great white. An adult megalodon's teeth could grow as large as nearly 7 inches.

"The megalodon shark was the apex predator in the water," Bischoff said.

Many other fish swam alongside these giant hunters. The bone beds also included an extinct saber-tooth salmon. The unusual-looking fish, which had large, protruding teeth, had never been found in Southern California before.

In addition to megalodon teeth, the oldest bone bed also contained lots of coprolites, fossilized poop full of fish bones.

The fossilized waste can help researchers learn exactly which animals were predators and prey. "That's what's so fun about paleontology," Hendy said. "It's detective work, so this is the classic whodunit. Who was eating who or being eaten by whom?"

Eighth-grader Decker Cullen got hands-on experience with the coprolite at Envicom Corporation as part of a school project.

Other SPHS students will soon get even more involved with the fossils that were once beneath their feet. They'll work on murals, publications, and research projects, Bischoff said.

At the Natural History Museum, Hendy has had kids sort some of the 120,000-year-old shells. "The kids love it, and it's a very, very easy sort of pathway into doing some real paleontology," he said.

Bischoff has worked on many other sites but said, "The SPHS site is entirely unique." That's because of the huge amount of fossils they found there.

"The NHM team has stated that it is the largest marine bonebed ever found in Los Angeles and Orange Counties," he said.

The work of analyzing the fossils is still in its early stages. Researchers at the museum will continue studying the fossils and hope to publish some of their findings in 2025.

The Los Angeles Unified School District and Cabrillo Aquarium plan to display their collections and use them for educational programs.

Eventually, the high school will have its own exhibit on the fossil finds. Hendy plans to have a future student intern design it.